《生物质能工程》课程教学资源（阅读材料）2. 催化热解 Optimizing

Applied Catalysis A:General 423-424(2012)154-161 Contents lists available at SciVerse ScienceDirect CECAIALYSS Applied Catalysis A:General ELSEVIER journal homepage:www.elsevier.com/locate/apcata Optimizing the aromatic yield and distribution from catalytic fast pyrolysis of biomass over ZSM-5 Andrew J.Fostera,Jungho Jaeb.1,Yu-Ting Chengb,George W.Huberb,Raul F.Loboa. Center for Catalytic Science and Technology,Department of Chemical Engineering.University of Delaware,Newark,DE 19716.USA Department of Chemical Engineering University of Massachusetts-Amherst.159Goessmann Lab,Amherst,MA01003.USA ARTICLE INFO ABSTRACT Article history: The conversion of glucose,furan and maple wood has been investigated over different types of ZSM-5 Received 14 September 2011 catalyst in semi-batch and fixed-bed reactors.The aromatic yield from glucose conversion goes through Received in revised form 15 February 2012 a maximum as a function of the framework silica-to-alumina ratio(SAR)of ZSM-5 with an optimum at Accepted 18 February 2012 Available online 27 February 2012 SAR-30.This suggests that the concentration of acid sites inside the zeolite is critical for maximizing aromatic yield.Creating hierarchical mesopores within the zeolite slightly increased of coke formation Keywords: and decreased the formation of the monocyclic aromatics.Mesoporous ZSM-5 was also observed to favor ZSM-5 the production of larger alkylated monoaromatics.The selective removal of external acid sites from the Zeolite ZSM-5 catalysts only slightly increased the catalyst activity but also decreased the selectivity to the Catalyst desired aromatic products. Biomass 2012 Elsevier B.V.All rights reserved. Pyrolysis 1.Introduction engines [2].It also has an energy density much lower than that of crude oil,in large part due to its oxygen content [8].Pyrolysis oils Biomass is an abundant,renewable source of carbon that can be require catalytic upgrading to remove oxygen functional groups used as a feedstock for liquid transportation fuels [1].Challenges before they are compatible with existing fuel infrastructure. exist in the efficient conversion of biomass to fuels compatible with Catalytic fast pyrolysis(CFP)is a further modification of fast internal combustion engines.Solid biomass must be converted to pyrolysis directed towards the production of hydrocarbon fuels. liquids at high yields,and these liquids must have a high energy By pyrolyzing biomass in the presence of a catalyst,it is possible density and be easily combustible [1].Fast pyrolysis is one route to catalyze the direct production of aromatic hydrocarbons such for the conversion of biomolecules to generate liquid products[2]. as benzene,toluene,and xylenes [9-16].forgoing the need for an High temperature thermal degradation of biomass in the absence additional upgrading reactor.CFP has several advantages over other of oxygen followed by rapid cooling makes it possible to recover a biomass conversion approaches.All of the desired chemistry can large fraction of the original feedstock in the form of liquid pyroly- occur in a single reactor using inexpensive aluminosilicate cata- sis oils [3].Pyrolysis technology has several advantages over other lysts.CFP can be used to process a range of different lignocellulosic biomass liquefaction processes:it requires only a single reactor and feedstocks with only simple pretreatment(drying and grinding,for operates at very short contact times in contrast to biomass fermen- example)prior to reaction.The aromatics produced through CFP tation processes where reactor residence times are often multiple can readily be blended into the existing gasoline infrastructure to days [4].Product separations are less energy intensive in pyrolysis- reduce the use of crude oil. based processes,as the liquid products generated are concentrated Zeolites have been shown to be effective catalysts for the compared to the aqueous ethanol produced in fermentation [4.In aromatization of a wide range of non-oxygenated and oxygenated addition,pyrolysis may be used to convert a wide range of feed- feedstocks [17-19].so it is not surprising that they are capable stocks [5-7]that are difficult to process through enzymatic routes. of performing the same reactions over oxygenates from biomass However,due to its high oxygen content biomass pyrolysis oil is Zeolites have been known to catalyze the direct conversion of too acidic,viscous,and chemically unstable for use in combustion carbohydrates to aromatics and olefins since early 1980s [20,21]. Chen et al.showed glucose and xylose could be converted to aro- matic hydrocarbons over HZSM-5 with low yields.Since then, Corresponding author.Tel.:+1 302 831 1261:fax:+1 302 831 2085 several studies have been performed on the use of zeolites as E-mail address:lobo@udel.edu(R.F.Lobo). catalysts for pyrolysis oil upgrading [22-27].Adjaye and Bakhshi 1 Co-first author. [22,23]reported that pyrolysis oil can be upgraded to produce 0926-860X/S-see front matter2012 Elsevier B.V.All rights reserved. doi:10.1016 japcata.2012.02.030

Applied Catalysis A: General 423–424 (2012) 154–161 Contents lists available at SciVerse ScienceDirect Applied Catalysis A: General j ournal homepage: www.elsevier.com/locate/apcata Optimizing the aromatic yield and distribution from catalytic fast pyrolysis of biomass over ZSM-5 Andrew J. Foster a, Jungho Jae b,1, Yu-Ting Cheng b, George W. Huber b, Raul F. Loboa,∗ a Center for Catalytic Science and Technology, Department of Chemical Engineering, University of Delaware, Newark, DE 19716, USA b Department of Chemical Engineering, University of Massachusetts-Amherst, 159 Goessmann Lab, Amherst, MA 01003, USA a r t i c l e i n f o Article history: Received 14 September 2011 Received in revised form 15 February 2012 Accepted 18 February 2012 Available online 27 February 2012 Keywords: ZSM-5 Zeolite Catalyst Biomass Pyrolysis a b s t r a c t The conversion of glucose, furan and maple wood has been investigated over different types of ZSM-5 catalyst in semi-batch and fixed-bed reactors. The aromatic yield from glucose conversion goes through a maximum as a function of the framework silica-to-alumina ratio (SAR) of ZSM-5 with an optimum at SAR = 30. This suggests that the concentration of acid sites inside the zeolite is critical for maximizing aromatic yield. Creating hierarchical mesopores within the zeolite slightly increased of coke formation and decreased the formation of the monocyclic aromatics. Mesoporous ZSM-5 was also observed to favor the production of larger alkylated monoaromatics. The selective removal of external acid sites from the ZSM-5 catalysts only slightly increased the catalyst activity but also decreased the selectivity to the desired aromatic products. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Biomass is an abundant, renewable source of carbon that can be used as a feedstock for liquid transportation fuels [1]. Challenges existin the efficient conversion of biomass to fuels compatible with internal combustion engines. Solid biomass must be converted to liquids at high yields, and these liquids must have a high energy density and be easily combustible [1]. Fast pyrolysis is one route for the conversion of biomolecules to generate liquid products [2]. High temperature thermal degradation of biomass in the absence of oxygen followed by rapid cooling makes it possible to recover a large fraction of the original feedstock in the form of liquid pyroly￾sis oils [3]. Pyrolysis technology has several advantages over other biomass liquefaction processes:it requires only a single reactor and operates at very short contact times in contrast to biomass fermen￾tation processes where reactor residence times are often multiple days [4]. Product separations are less energy intensive in pyrolysis￾based processes, as the liquid products generated are concentrated compared to the aqueous ethanol produced in fermentation [4]. In addition, pyrolysis may be used to convert a wide range of feed￾stocks [5–7] that are difficult to process through enzymatic routes. However, due to its high oxygen content biomass pyrolysis oil is too acidic, viscous, and chemically unstable for use in combustion ∗ Corresponding author. Tel.: +1 302 831 1261; fax: +1 302 831 2085. E-mail address: lobo@udel.edu (R.F. Lobo). 1 Co-first author. engines [2]. It also has an energy density much lower than that of crude oil, in large part due to its oxygen content [8]. Pyrolysis oils require catalytic upgrading to remove oxygen functional groups before they are compatible with existing fuel infrastructure. Catalytic fast pyrolysis (CFP) is a further modification of fast pyrolysis directed towards the production of hydrocarbon fuels. By pyrolyzing biomass in the presence of a catalyst, it is possible to catalyze the direct production of aromatic hydrocarbons such as benzene, toluene, and xylenes [9–16], forgoing the need for an additional upgrading reactor. CFP has several advantages over other biomass conversion approaches. All of the desired chemistry can occur in a single reactor using inexpensive aluminosilicate cata￾lysts. CFP can be used to process a range of different lignocellulosic feedstocks with only simple pretreatment (drying and grinding, for example) prior to reaction. The aromatics produced through CFP can readily be blended into the existing gasoline infrastructure to reduce the use of crude oil. Zeolites have been shown to be effective catalysts for the aromatization of a wide range of non-oxygenated and oxygenated feedstocks [17–19], so it is not surprising that they are capable of performing the same reactions over oxygenates from biomass. Zeolites have been known to catalyze the direct conversion of carbohydrates to aromatics and olefins since early 1980s [20,21]. Chen et al. showed glucose and xylose could be converted to aro￾matic hydrocarbons over HZSM-5 with low yields. Since then, several studies have been performed on the use of zeolites as catalysts for pyrolysis oil upgrading [22–27]. Adjaye and Bakhshi [22,23] reported that pyrolysis oil can be upgraded to produce 0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2012.02.030

AJ.Foster et al./Applied Catalysis A:General 423-424(2012)154-161 155 hydrocarbons over an HZSM-5 catalyst with aromatic yields up of different conditions,giving rise to different crystal sizes,mor- to 27 wt%.They also showed that HZSM-5 was much more active phologies,and elemental compositions.This flexibility allows for an than silicalite-1,suggesting that Bronsted acid sites have a criti- effort to study some of the factors affecting the aromatic yield from cal role in the upgrading reactions.Other investigators obtained biomass pyrolysis in detail to develop a better understanding of similar aromatic yields from the catalytic upgrading of pyrolysis biomass catalytic fast pyrolysis and to create a better ZSM-5-based oils from maple wood [26]and Canadian oak [28]over HZSM-5 pyrolysis catalyst. catalysts.ZSM-5 has also been shown to be the most active and One simple method to increase the yield towards aromatics may selective catalyst for the conversion of aqueous sugar solutions to be to increase the density of available catalytic sites.Zeolites with hydrocarbons [29].Gayubo et al.[24]found that oxygenates such higher aluminum content will have more acid sites able to catalyze as furfural and guaiacol contribute to rapid coke formation and the series of reactions necessary to form aromatics.However,as catalyst deactivation on HZSM-5 during pyrolysis oil upgrading. more aluminum is incorporated into the zeolite framework,the Model biomass compounds can be used to develop an under- zeolite will become more hydrophilic [31]and the appearance of standing ofthe catalytic factors which influence the overall reaction closely located Bronsted acid sites may have an effect on the cat- and aid in the design of CFP catalysts.We have previously shown alytic chemistry within the zeolite.This suggests that an optimum that furan and glucose are good model compounds for studying cel- silica-to-alumina ratio (SAR)may exist for this reaction.Since the lulose catalytic fast pyrolysis as CFP of all these compounds gave glucose derivatives in the proposed reaction scheme are compara- similar product selectivities [9,10,13,14].The proposed reaction ble in size to the micropore openings of zeolites [15].one strategy chemistry for glucose CFP is shown in Scheme 1.Glucose pyrol- to improve the conversion of these molecules is to improve the dif- ysis begins with a dehydration reaction to form anhydrosugars fusion characteristics of the catalysts.This may be accomplished by such as levoglucosan [11].Glucose can also undergo retro-aldol either decreasing the size of the zeolite particles or by creating hier- condensation to form dihydroxyacetone and glyceraldehydes.The archical mesopores within the zeolite framework [32].Because the anhydrosugars undergo further dehydration to form furanic species catalytic conversion of these molecules is likely limited by diffu- and water.These furans then undergo a series of decarbonylation sion into the micropores,any improvement in access to micropore and oligomerization reactions inside the zeolite to form a carbo- openings will have a positive effect on the ability of the zeolites to cation hydrocarbon pool and carbon monoxide.This hydrocarbon catalyze the desired reactions.As a side effect,the increased surface pool can then be converted into non-oxygenated olefins,monocylic area will also lead to an increase in the number of external surface aromatics and polycyclic aromatics.Coke can form on the catalyst acid sites. surface through parallel reactions of anhydrosugars,furans and the Because reactions confined within the zeolite micropores ben- hydrocarbon pool. efit from shape-selectivity,they are likely the key sites for the It has been shown that the micropore openings in ZSM-5 have formation of monoaromatic species.Acid sites on external particle a size near to the optimum for conversion of glucose towards surfaces and mesopore walls may have different activity and selec- aromatic species [15].This is due to the similarity between the tivity than the micropore sites [33].Selectively deactivating these diameter of benzene and the size of the largest micropore open- sites makes it possible to study their role during catalytic fast pyrol- ings in the zeolite.We have previously studied the effect of zeolite ysis.Deactivation can be accomplished by using a silylating agent micropore dimensions on glucose CFP using a range of small-, to make the sites inaccessible or by selective leaching from the zeo- medium-,and large-pore zeolites [15.The estimated kinetic diam- lite surface using an acid treatment.If the silylating/dealuminating eters of the reactants and products were used to determine whether agent used is larger than the micropores of the zeolite,the acid sites the reactions are able to occur inside the micropores or are limited on exterior surfaces can be selectively deactivated. to external surface sites for different zeolite catalysts.This analy- We have investigated the effects of modifying ZSM-5 bulk sis showed that the majority of aromatics and oxygenated species silica-to-alumina ratio,incorporating hierarchical mesopores,and present during reaction can fit inside the pores of most medium- selectively removing external surface acid sites on the CFP of glu- and large-pore zeolites but are excluded from entering small pores. cose,furan,and maple wood.Each of these aspects of the catalyst We showed that the aromatic yield is a function of the pore size of can alter both the activity for conversion of biomass derivatives and the zeolite catalyst.Zeolites with smaller micropores than ZSM- the selectivity for desirable hydrocarbon products.Understanding 5 severely hinder the diffusion of both reactants (i.e.furans)and the impact of these factors can be used to design more effective products(i.e.xylenes)in glucose pyrolysis.Small-pore zeolites did catalysts for the conversion of biomass to aromatics through CFP. not produce any aromatics from glucose,instead producing a mix- ture ofoxygenates,CO,CO2 and coke.In these cases,most reactions are limited to sites on the exterior particle surfaces [30]and coke is 2.Materials and methods the primary product.Zeolites with large pores allow for faster reac- tant diffusion,but the formation of larger polyaromatics within the 2.1.Zeolite synthesis zeolite micropores becomes more prevalent due to the lack of reac- tant confinement.Large-pore zeolites also primarily produce coke Mesoporous ZSM-5 (MesZSM-5)was synthesized using the during fast pyrolysis.Aromatic yields were highest in the medium- surfactant-mediated method reported by Ryoo et al.[34].3- pore zeolites with pore sizes in the range of 5.2-5.9A.In addition (Trimethoxysilyl)propyl dimethyl octadecyl ammonium chloride to micropore diameter,internal pore space and steric hindrance (TMPDOA)was used as a mesoporogen,and sodium aluminate was played a determining role for aromatic production.Medium-pore used as aluminum source.The synthesis gel had a molar oxide zeolites with moderate internal pore space and steric hindrance composition of40Na20:95 SiO2:3.3Al203:5TPA2O:26H2SO4:9000 (ZSM-5 and ZSM-11)gave the highest aromatic yield and the least H2O:5 TMPDOA.Samples were then crystallized in Parr Acid Diges coke formation.This study suggested that the ZSM-5 structure was tion Vessels under autogenous pressure at 150C for 4 days. the optimal zeolite structure for biomass conversion into aromatics. Non-mesoporous samples of ZSM-5 (MicZSM-5)were also The objective of this paper is to study how ZSM-5 can be further synthesized using tetrapropylammonium (TPA)as a structure- modified to increase the aromatic selectivity for CFP of biomass directing agent.The synthesis gel had a molar oxide composition The effects of ZSM-5 composition and mesoporosity on the yield of 5 Na20:100 SiO2:3.3 Al203:8 TPA2O:3000 H2O.Samples were and distribution of aromatics from glucose and maple wood CFP then loaded into Parr Acid Digestion Vessels and hydrothermally are studied in detail.ZSM-5 can be synthesized under a wide range synthesized under autogenous pressure at 150C for 5 days

A.J. Foster et al. / Applied Catalysis A: General 423–424 (2012) 154–161 155 hydrocarbons over an HZSM-5 catalyst with aromatic yields up to 27 wt%. They also showed that HZSM-5 was much more active than silicalite-1, suggesting that Brønsted acid sites have a criti￾cal role in the upgrading reactions. Other investigators obtained similar aromatic yields from the catalytic upgrading of pyrolysis oils from maple wood [26] and Canadian oak [28] over HZSM-5 catalysts. ZSM-5 has also been shown to be the most active and selective catalyst for the conversion of aqueous sugar solutions to hydrocarbons [29]. Gayubo et al. [24] found that oxygenates such as furfural and guaiacol contribute to rapid coke formation and catalyst deactivation on HZSM-5 during pyrolysis oil upgrading. Model biomass compounds can be used to develop an under￾standing ofthe catalytic factors which influence the overall reaction and aid in the design of CFP catalysts. We have previously shown thatfuran and glucose are good model compounds for studying cel￾lulose catalytic fast pyrolysis as CFP of all these compounds gave similar product selectivities [9,10,13,14]. The proposed reaction chemistry for glucose CFP is shown in Scheme 1. Glucose pyrol￾ysis begins with a dehydration reaction to form anhydrosugars such as levoglucosan [11]. Glucose can also undergo retro-aldol condensation to form dihydroxyacetone and glyceraldehydes. The anhydrosugarsundergo furtherdehydrationto formfuranic species and water. These furans then undergo a series of decarbonylation and oligomerization reactions inside the zeolite to form a carbo￾cation hydrocarbon pool and carbon monoxide. This hydrocarbon pool can then be converted into non-oxygenated olefins, monocylic aromatics and polycyclic aromatics. Coke can form on the catalyst surface through parallel reactions of anhydrosugars, furans and the hydrocarbon pool. It has been shown that the micropore openings in ZSM-5 have a size near to the optimum for conversion of glucose towards aromatic species [15]. This is due to the similarity between the diameter of benzene and the size of the largest micropore open￾ings in the zeolite. We have previously studied the effect of zeolite micropore dimensions on glucose CFP using a range of small-, medium-, and large-pore zeolites [15]. The estimated kinetic diam￾eters ofthe reactants and products wereused to determine whether the reactions are able to occur inside the micropores or are limited to external surface sites for different zeolite catalysts. This analy￾sis showed that the majority of aromatics and oxygenated species present during reaction can fit inside the pores of most medium￾and large-pore zeolites but are excluded from entering small pores. We showed that the aromatic yield is a function of the pore size of the zeolite catalyst. Zeolites with smaller micropores than ZSM- 5 severely hinder the diffusion of both reactants (i.e. furans) and products (i.e. xylenes) in glucose pyrolysis. Small-pore zeolites did not produce any aromatics from glucose, instead producing a mix￾ture of oxygenates, CO, CO2 and coke. In these cases, most reactions are limited to sites on the exterior particle surfaces [30] and coke is the primary product. Zeolites with large pores allow for faster reac￾tant diffusion, but the formation of larger polyaromatics within the zeolite micropores becomes more prevalent due to the lack of reac￾tant confinement. Large-pore zeolites also primarily produce coke during fast pyrolysis. Aromatic yields were highest in the medium￾pore zeolites with pore sizes in the range of 5.2–5.9A. ˚ In addition to micropore diameter, internal pore space and steric hindrance played a determining role for aromatic production. Medium-pore zeolites with moderate internal pore space and steric hindrance (ZSM-5 and ZSM-11) gave the highest aromatic yield and the least coke formation. This study suggested that the ZSM-5 structure was the optimal zeolite structure for biomass conversioninto aromatics. The objective of this paper is to study how ZSM-5 can be further modified to increase the aromatic selectivity for CFP of biomass. The effects of ZSM-5 composition and mesoporosity on the yield and distribution of aromatics from glucose and maple wood CFP are studied in detail. ZSM-5 can be synthesized under a wide range of different conditions, giving rise to different crystal sizes, mor￾phologies, and elemental compositions. Thisflexibility allows for an effort to study some of the factors affecting the aromatic yield from biomass pyrolysis in detail to develop a better understanding of biomass catalytic fast pyrolysis and to create a better ZSM-5-based pyrolysis catalyst. One simple method to increase the yield towards aromatics may be to increase the density of available catalytic sites. Zeolites with higher aluminum content will have more acid sites able to catalyze the series of reactions necessary to form aromatics. However, as more aluminum is incorporated into the zeolite framework, the zeolite will become more hydrophilic [31] and the appearance of closely located Brønsted acid sites may have an effect on the cat￾alytic chemistry within the zeolite. This suggests that an optimum silica-to-alumina ratio (SAR) may exist for this reaction. Since the glucose derivatives in the proposed reaction scheme are compara￾ble in size to the micropore openings of zeolites [15], one strategy to improve the conversion of these molecules is to improve the dif￾fusion characteristics of the catalysts. This may be accomplished by either decreasing the size ofthe zeolite particles or by creating hier￾archical mesopores within the zeolite framework [32]. Because the catalytic conversion of these molecules is likely limited by diffu￾sion into the micropores, any improvement in access to micropore openings will have a positive effect on the ability of the zeolites to catalyze the desired reactions. As a side effect,the increased surface area will also lead to an increase in the number of external surface acid sites. Because reactions confined within the zeolite micropores ben￾efit from shape-selectivity, they are likely the key sites for the formation of monoaromatic species. Acid sites on external particle surfaces and mesopore walls may have different activity and selec￾tivity than the micropore sites [33]. Selectively deactivating these sites makes it possible to study their role during catalytic fast pyrol￾ysis. Deactivation can be accomplished by using a silylating agent to make the sites inaccessible or by selective leaching from the zeo￾lite surface using an acid treatment. If the silylating/dealuminating agent used is larger than the micropores ofthe zeolite,the acid sites on exterior surfaces can be selectively deactivated. We have investigated the effects of modifying ZSM-5 bulk silica-to-alumina ratio, incorporating hierarchical mesopores, and selectively removing external surface acid sites on the CFP of glu￾cose, furan, and maple wood. Each of these aspects of the catalyst can alter both the activity for conversion of biomass derivatives and the selectivity for desirable hydrocarbon products. Understanding the impact of these factors can be used to design more effective catalysts for the conversion of biomass to aromatics through CFP. 2. Materials and methods 2.1. Zeolite synthesis Mesoporous ZSM-5 (MesZSM-5) was synthesized using the surfactant-mediated method reported by Ryoo et al. [34]. 3- (Trimethoxysilyl)propyl dimethyl octadecyl ammonium chloride (TMPDOA) was used as a mesoporogen, and sodium aluminate was used as aluminum source. The synthesis gel had a molar oxide composition of 40 Na2O:95 SiO2:3.3Al2O3:5 TPA2O:26 H2SO4:9000 H2O:5 TMPDOA. Samples were then crystallized in Parr Acid Diges￾tion Vessels under autogenous pressure at 150 ◦C for 4 days. Non-mesoporous samples of ZSM-5 (MicZSM-5) were also synthesized using tetrapropylammonium (TPA) as a structure￾directing agent. The synthesis gel had a molar oxide composition of 5 Na2O:100 SiO2:3.3 Al2O3:8 TPA2O:3000 H2O. Samples were then loaded into Parr Acid Digestion Vessels and hydrothermally synthesized under autogenous pressure at 150 ◦C for 5 days

156 AJ.Foster et aL Applied Catalysis A:General 423-424(2012)154-161 Glucose Monocyclic Aromatics Anhydrosugars Furans HO x HO L yco, OH z HCOH Hydrocarbo OH Polyeyclic Aromatics x H2O xHO xHO yCOx yCOx COKE Scheme 1.Proposed reaction chemistry for glucose CFP over ZSM-5. Adapted from Ref.[11]. After synthesis,zeolite samples were washed repeatedly with 2.4.Catalytic testing water,filtered and dried overnight at 80C.Samples were then cal- cined in air at 550C for 6 h to remove occluded organic molecules. Catalytic testing of the zeolite samples for conversion of glucose Zeolite samples were ion-exchanged to the ammonium form by and maple wood was carried out using a semi-batch Pyroprobe treatment in 0.1 M NH4NO at 70C for 24h followed by filtration, reaction system coupled with a HP 5890 Series ll gas chromato- and drying at 80C.The samples were then calcined again at 550C graph and HP 5792 Series mass-selective detector.During a typical to prepare the acid form of the zeolite before catalytic testing. test,a physical mixture consisting of 95 wt%ZSM-5 and 5 wt%glu- Samples used to study the effect of framework SiO2/Al2O3 were cose was prepared and inserted into the reaction chamber.The obtained from Zeolyst with silica-to-alumina ratios of 23,30,50 chamber was heated at a nominal rate of 1000C/s to a final reac- and 80. tion temperature of 600C.Products from the reaction cell were analyzed by GC-MSD.The reaction procedure is described in detail 2.2.Surface dealumination in a previous report 12.The aromatic yield is calculated as the sum of the yields of all non-oxygenated carbon species volatile enough Zeolite samples in the acid form were treated in a 2M L- to be analyzed by the in-line GC.Carbon content in the form of coke tartaric acid solution in water for 1 h at 70C to selectively remove was calculated from combustion elemental analysis performed by surface acid sites (MicZSM-5*and MesZSM-5).After treatment Galbraith Laboratories(Knoxville,TN)after reaction.Mass balances samples were quickly cooled to room temperature,filtered and were calculated on a molar carbon basis.Carbon balances including dried at 80C.The samples were then ion-exchanged with aque- coke,gas products,and aromatics were between 90 and 105%in all ous ammonium nitrate and calcined again as described above.The semi-batch experiments effectiveness of the acid treatment for removal of surface aluminum Conversion of furan was carried out in a 0.5 in.diameter flow was quantified using X-ray photoelectron spectroscopy.The bulk fixed bed reactor.Approximately 57mg of catalyst was loaded composition of the ZSM-5 particles was measured before and after in the reactor.Prior to reaction,the catalyst bed was calcined dealumination using energy dispersive X-ray spectroscopy(EDS) in helium (Airgas,ultra-high purity)at 600C.Furan was fed using a Jeol JSM 7400FScanning Electron Microscope.Samples were via syringe pump (Fisher,KDS100)at a rate of 0.58mL/h into coated with gold using a Denton Vacuum Desk IV sputtering system 408 mL/min ofhelium,resulting in a furan partial pressure of 6 Torr prior to EDS measurements. The furan-containing stream was bypassed around the reactor for 30 min before switching to flow through the reactor.During 2.3.Analytical reaction,the catalyst bed was maintained at 600C and ambient pressure.An air bath condenser was used to trap heavy prod- Powder X-ray diffraction patterns were obtained using a Philips ucts,and gas-phase products were collected in gas sampling bags X'Pert Diffractometer operated at 45kV and 40mA using a Cu After 270s of reaction,the flow of furan was stopped and the source.Electron micrographs and energy dispersive X-ray spectra reactor was flushed with helium for 45 s.The spent catalyst was of zeolite samples were collected using a Jeol JSM 7400F Scan- then treated in air at 600C to burn off accumulated coke.Any ning Electron Microscope.Samples were first coated with gold CO produced was further converted to CO2 over a bed of Cuo using a Denton Vacuum Desk IV sputtering system.X-ray photo- (Sigma-Aldrich)at 240C.The CO2 was trapped by a CO2 trap electron spectra were recorded using a Physical Electronics XPS (Ascarite,Sigma-Aldrich).Coke yield was calculated by measuring system equipped with an Al-anode X-ray generator and multi- the weight change of the COz trap.Gas-phase reaction products channel hemispherical analyzer.Textural characterization of the were analyzed by GC-FID(Shimadzu GC-2014).Gaseous species samples was carried out with a Micromeritics ASAP 2010 adsorp- and coke deposited on the catalyst accounted for the vast majority tion instrument using N2 gas.Samples were degassed overnight of products.In our study,heavy products condensed in the liquid under vacuum at 320C prior to the measurement.Isotherms trap accounted for less than 0.05%of the total carbon fed through were analyzed using the t-plot method to calculate microporous the reactor.As in the semi-batch reactor experiments,mass bal- volume.The mesoporous volume and size distribution were calcu- ances were calculated on a molar carbon basis.Carbon balances lated using the Barrett-Joyner-Halenda method on the adsorption including coke,gas products,and aromatics ranged from 97 to branch of the isotherm. 107%in all fixed bed reactor experiments.Incomplete removal

156 A.J. Foster et al. / Applied Catalysis A: General 423–424 (2012) 154–161 O H OH OH OH OH OH O HO HO OH OH OH H2O O O HO OH OH O x HO HO OH O Glucose Anhydrosugars O O O O OH HO O Furans x H2O yCOx z HCOH Hydrocarbon Pool x H2O yCOx x H2O yCOx COKE Monocyclic Aromatics Polycyclic Aromatics x H2O yCOx x H2O yCOx Scheme 1. Proposed reaction chemistry for glucose CFP over ZSM-5. Adapted from Ref. [11]. After synthesis, zeolite samples were washed repeatedly with water, filtered and dried overnight at 80 ◦C. Samples were then cal￾cined in air at 550 ◦C for 6 h to remove occluded organic molecules. Zeolite samples were ion-exchanged to the ammonium form by treatment in 0.1 M NH4NO3 at 70 ◦C for 24 h followed by filtration, and drying at 80 ◦C. The samples were then calcined again at 550 ◦C to prepare the acid form of the zeolite before catalytic testing. Samples used to study the effect of framework SiO2/Al2O3 were obtained from Zeolyst with silica-to-alumina ratios of 23, 30, 50 and 80. 2.2. Surface dealumination Zeolite samples in the acid form were treated in a 2 M l￾tartaric acid solution in water for 1 h at 70 ◦C to selectively remove surface acid sites (MicZSM-5* and MesZSM-5*). After treatment, samples were quickly cooled to room temperature, filtered and dried at 80 ◦C. The samples were then ion-exchanged with aque￾ous ammonium nitrate and calcined again as described above. The effectiveness ofthe acid treatmentfor removal of surface aluminum was quantified using X-ray photoelectron spectroscopy. The bulk composition of the ZSM-5 particles was measured before and after dealumination using energy dispersive X-ray spectroscopy (EDS) using a JeolJSM7400F Scanning ElectronMicroscope. Samples were coated with gold using a Denton Vacuum Desk IV sputtering system prior to EDS measurements. 2.3. Analytical Powder X-ray diffraction patterns were obtained using a Philips X’Pert Diffractometer operated at 45 kV and 40 mA using a Cu source. Electron micrographs and energy dispersive X-ray spectra of zeolite samples were collected using a Jeol JSM 7400F Scan￾ning Electron Microscope. Samples were first coated with gold using a Denton Vacuum Desk IV sputtering system. X-ray photo￾electron spectra were recorded using a Physical Electronics XPS system equipped with an Al-anode X-ray generator and multi￾channel hemispherical analyzer. Textural characterization of the samples was carried out with a Micromeritics ASAP 2010 adsorp￾tion instrument using N2 gas. Samples were degassed overnight under vacuum at 320 ◦C prior to the measurement. Isotherms were analyzed using the t-plot method to calculate microporous volume. The mesoporous volume and size distribution were calcu￾lated using the Barrett–Joyner–Halenda method on the adsorption branch of the isotherm. 2.4. Catalytic testing Catalytic testing of the zeolite samples for conversion of glucose and maple wood was carried out using a semi-batch Pyroprobe reaction system coupled with a HP 5890 Series II gas chromato￾graph and HP 5792 Series mass-selective detector. During a typical test, a physical mixture consisting of 95 wt% ZSM-5 and 5 wt% glu￾cose was prepared and inserted into the reaction chamber. The chamber was heated at a nominal rate of 1000 ◦C/s to a final reac￾tion temperature of 600 ◦C. Products from the reaction cell were analyzed by GC-MSD. The reaction procedure is described in detail in a previous report[12]. The aromatic yield is calculated as the sum of the yields of all non-oxygenated carbon species volatile enough to be analyzed by the in-line GC. Carbon content in the form of coke was calculated from combustion elemental analysis performed by Galbraith Laboratories (Knoxville, TN) after reaction. Mass balances were calculated on a molar carbon basis. Carbon balances including coke, gas products, and aromatics were between 90 and 105% in all semi-batch experiments. Conversion of furan was carried out in a 0.5 in. diameter flow fixed bed reactor. Approximately 57 mg of catalyst was loaded in the reactor. Prior to reaction, the catalyst bed was calcined in helium (Airgas, ultra-high purity) at 600 ◦C. Furan was fed via syringe pump (Fisher, KDS100) at a rate of 0.58 mL/h into 408 mL/min of helium, resulting in a furan partial pressure of 6 Torr. The furan-containing stream was bypassed around the reactor for 30 min before switching to flow through the reactor. During reaction, the catalyst bed was maintained at 600 ◦C and ambient pressure. An air bath condenser was used to trap heavy prod￾ucts, and gas-phase products were collected in gas sampling bags. After 270 s of reaction, the flow of furan was stopped and the reactor was flushed with helium for 45 s. The spent catalyst was then treated in air at 600 ◦C to burn off accumulated coke. Any CO produced was further converted to CO2 over a bed of CuO (Sigma–Aldrich) at 240 ◦C. The CO2 was trapped by a CO2 trap (Ascarite, Sigma–Aldrich). Coke yield was calculated by measuring the weight change of the CO2 trap. Gas-phase reaction products were analyzed by GC-FID (Shimadzu GC-2014). Gaseous species and coke deposited on the catalyst accounted for the vast majority of products. In our study, heavy products condensed in the liquid trap accounted for less than 0.05% of the total carbon fed through the reactor. As in the semi-batch reactor experiments, mass bal￾ances were calculated on a molar carbon basis. Carbon balances including coke, gas products, and aromatics ranged from 97 to 107% in all fixed bed reactor experiments. Incomplete removal

AJ.Foster et al.Applied Catalysis A:General 423-424(2012)154-161 157 Table 1 a田Unidentified Microporous and mesoporous volumes of samples used for SiOz/Al2O3 study as 100 Coke measured by N2 adsorption. 90 Sample Vmicro (cm3/g) Vmeso(cm3/g) ZSM-5.SAR=23 0.115 0.029 ZSM-5,SAR=30 0.107 0.056 ZSM-5.SAR=50 60 0.124 0.059 ZSM-5.SAR=80 0.119 0.077 of occluded organic structure-directing molecules after zeolite synthesis,as well as experimental error in the quantification of coke 20 and product gases likely contributed to any mass balances above 10- 100%. 0 23 30 50 0 3.Results and discussion Bulk Sio,/Al,O Fig.1.Yield of aromatic hydrocarbons,CO2.and CO from catalytic fast pyrolysis Experiments were conducted to determine the relationship of glucose over ZSM-5 with varying SiOz/Al2O composition.Reaction conditions: between different properties of ZSM-5 catalysts on the yield and 600C.19mg catalyst/mg glucose,and 240s reaction time. distribution of aromatic hydrocarbons obtained through glucose and maple wood catalytic fast pyrolysis.The key parameters necessary to limit bimolecular coke-forming reactions.As the investigated were bulk silica-to-alumina ratio,mesoporosity and silica-to-alumina ratio of ZSM-5 is decreased.the concentration of removal of external surface acid sites. acid sites in close proximity to one another will increase.The incor- poration of these additional acid sites in closer proximity to each 3.1.Optimizing aromatic yield by tuning Al content of ZSM-5 other may promote secondary reactions responsible for converting aromatic species to coke within the micropores.This effect of acid- Changing the alumina content of the zeolite particles will impact site density enhances the rate of coke formation in the conversion both the hydrophilicity of the catalyst [31]and the number density of methanol to olefins over ZSM-5 catalysts with similar SAR [39]. of Bronsted acid sites and hence may impact the aromatic yield [35]. Similar effects of the silica-to-alumina ratio on reactivity have also ZSM-5 can be synthesized over a wide range of silica-to-alumina been observed in the esterification of acetic acid and butanol over ratios,and this has an effect on its activity for biomass catalytic USY [40]and dodecane cracking over ZSM-5 [41]. fast pyrolysis.Four ZSM-5 samples (obtained from Zeolyst)with The amount of CO2 produced during the reaction depends different silica-to-alumina ratios(23,30,50,80)were tested for weakly on the Al content of the ZSM-5 samples.The sample with catalytic conversion of glucose to study the effect of changing the Al the highest aluminum content produced the highest amount of CO2. content in the catalyst.X-ray diffraction of the samples confirmed suggesting that the decarboxylation is enhanced by Bronsted acid that all were highly crystalline MFI-type framework materials(see catalysis but is less sensitive to acid site density than decarbonyla- supporting information). tion. Nitrogen adsorption measurements confirmed that all samples The distribution of aromatic hydrocarbon products from glu- had microporous volume of approximately 0.12 cm3/g and meso- cose pyrolysis changed slightly between samples as shown in Fig.2. porous volume between 0.03 and 0.08 cm3/g (see Table 1).SEM The ZSM-5 sample with the highest aluminum content showed images revealed that there were no visible morphological differ- the highest selectivity towards smaller aromatic products (ben- ences between the samples with different SAR (see supporting zene and toluene),and samples with a lower amount of aluminum information).The size of primary particles in the samples slightly were slightly more selective towards larger products (Cs*aro- decreased with decreasing aluminum content.The decrease in pri- matics and polyaromatics).The larger aromatic products included mary particle size led to an increase in the number of particle boundaries and voids within the samples,which likely accounts for the apparent increase in mesopore volume with SAR.However,the 45- Si0/AN,0,=23 observed mesoporous volume of these samples is modest,and is not 国Si0/AN,O2=30 expected to contribute significantly to the activity and selectivity of 40 ZZ☑Si0JA,0,=50 these samples during the CFP reaction.The effects of mesoporosity 图Si0/A,0,=80 is discussed in more detail in the following section. 35- The yield of aromatic products from glucose as a function of bulk 里 30- silica-to-alumina ratio is shown in Fig.1.The maximum aromatic yield occurred at SiO/Al2O3=30,with a concurrent minimum in 25 the amount of coke produced.The CO and CO2 produced during 20 pyrolysis are considered to be the products of decarbonylation and decarboxylation reactions,respectively [11].The strong Bronsted 15 acid sites in ZSM-5 have been shown to be active for the decar- bonylation of benzaldehydes [36]and furfurals [37].two types of compounds produced during biomass fast pyrolysis [38].The amount of CO produced is at a maximum for the SiO2/Al203=30 sample,suggesting that there may be a relationship between the rate of oxygen removal via decarbonylation and the formation C6 C7 C8 C9 Polyarom. of aromatic species.A silica-to-alumina ratio of 30 represents an Fig.2.Distribution of aromatic products from fast pyrolysis of glucose over ZSM-5 optimal composition for the high availability of Bronsted sites with varying SiOz/Al2O3 composition.Reaction conditions:600C.19mg cata- while simultaneously maintaining the distance between acid sites lyst/mg glucose,and 240s reaction time

A.J. Foster et al. / Applied Catalysis A: General 423–424 (2012) 154–161 157 Table 1 Microporous and mesoporous volumes of samples used for SiO2/Al2O3 study as measured by N2 adsorption. Sample Vmicro (cm3/g) Vmeso (cm3/g) ZSM-5, SAR = 23 0.115 0.029 ZSM-5, SAR = 30 0.107 0.056 ZSM-5, SAR = 50 0.124 0.059 ZSM-5, SAR = 80 0.119 0.077 of occluded organic structure-directing molecules after zeolite synthesis, as well as experimental error in the quantification of coke and product gases likely contributed to any mass balances above 100%. 3. Results and discussion Experiments were conducted to determine the relationship between different properties of ZSM-5 catalysts on the yield and distribution of aromatic hydrocarbons obtained through glucose and maple wood catalytic fast pyrolysis. The key parameters investigated were bulk silica-to-alumina ratio, mesoporosity and removal of external surface acid sites. 3.1. Optimizing aromatic yield by tuning Al content of ZSM-5 Changing the alumina content ofthe zeolite particles will impact both the hydrophilicity of the catalyst [31] and the number density of Brønsted acid sites and hence may impactthe aromatic yield [35]. ZSM-5 can be synthesized over a wide range of silica-to-alumina ratios, and this has an effect on its activity for biomass catalytic fast pyrolysis. Four ZSM-5 samples (obtained from Zeolyst) with different silica-to-alumina ratios (23, 30, 50, 80) were tested for catalytic conversion of glucose to study the effect of changing the Al content in the catalyst. X-ray diffraction of the samples confirmed that all were highly crystalline MFI-type framework materials (see supporting information). Nitrogen adsorption measurements confirmed that all samples had microporous volume of approximately 0.12 cm3/g and meso￾porous volume between 0.03 and 0.08 cm3/g (see Table 1). SEM images revealed that there were no visible morphological differ￾ences between the samples with different SAR (see supporting information). The size of primary particles in the samples slightly decreased with decreasing aluminum content. The decrease in pri￾mary particle size led to an increase in the number of particle boundaries and voids within the samples, which likely accounts for the apparent increase in mesopore volume with SAR. However, the observedmesoporous volume ofthese samples ismodest, andisnot expected to contribute significantly to the activity and selectivity of these samples during the CFP reaction. The effects of mesoporosity is discussed in more detail in the following section. The yield of aromatic products from glucose as a function of bulk silica-to-alumina ratio is shown in Fig. 1. The maximum aromatic yield occurred at SiO2/Al2O3 = 30, with a concurrent minimum in the amount of coke produced. The CO and CO2 produced during pyrolysis are considered to be the products of decarbonylation and decarboxylation reactions, respectively [11]. The strong Brønsted acid sites in ZSM-5 have been shown to be active for the decar￾bonylation of benzaldehydes [36] and furfurals [37], two types of compounds produced during biomass fast pyrolysis [38]. The amount of CO produced is at a maximum for the SiO2/Al2O3 = 30 sample, suggesting that there may be a relationship between the rate of oxygen removal via decarbonylation and the formation of aromatic species. A silica-to-alumina ratio of 30 represents an optimal composition for the high availability of Brønsted sites while simultaneously maintaining the distance between acid sites 23 30 50 80 0 10 20 30 40 50 60 70 80 90 100 Carbon Yield (%) Bulk SiO2 / Al2 O3 Unidentified Coke CO CO Aromatics Fig. 1. Yield of aromatic hydrocarbons, CO2, and CO from catalytic fast pyrolysis of glucose over ZSM-5 with varying SiO2/Al2O3 composition. Reaction conditions: 600 ◦C, 19 mg catalyst/mg glucose, and 240 s reaction time. necessary to limit bimolecular coke-forming reactions. As the silica-to-alumina ratio of ZSM-5 is decreased, the concentration of acid sites in close proximity to one another will increase. The incor￾poration of these additional acid sites in closer proximity to each other may promote secondary reactions responsible for converting aromatic species to coke within the micropores. This effect of acid￾site density enhances the rate of coke formation in the conversion of methanol to olefins over ZSM-5 catalysts with similar SAR [39]. Similar effects of the silica-to-alumina ratio on reactivity have also been observed in the esterification of acetic acid and butanol over USY [40] and dodecane cracking over ZSM-5 [41]. The amount of CO2 produced during the reaction depends weakly on the Al content of the ZSM-5 samples. The sample with thehighest aluminumcontentproducedthehighest amount ofCO2, suggesting that the decarboxylation is enhanced by Brønsted acid catalysis but is less sensitive to acid site density than decarbonyla￾tion. The distribution of aromatic hydrocarbon products from glu￾cose pyrolysis changed slightly between samples as shown in Fig. 2. The ZSM-5 sample with the highest aluminum content showed the highest selectivity towards smaller aromatic products (ben￾zene and toluene), and samples with a lower amount of aluminum were slightly more selective towards larger products (C8 + aro￾matics and polyaromatics). The larger aromatic products included C6 C7 C8 C9 Polyarom. 0 5 10 15 20 25 30 35 40 45 Aromatic Selectivity (%) SiO2 /Al2 O3 = 23 SiO2 /Al2 O3 = 30 SiO2 /Al2 O3 = 50 SiO2 /Al2 O3 = 80 Fig. 2. Distribution of aromatic products from fast pyrolysis of glucose over ZSM-5 with varying SiO2/Al2O3 composition. Reaction conditions: 600 ◦C, 19 mg cata￾lyst/mg glucose, and 240 s reaction time

158 AJ.Foster et al.Applied Catalysis A:General 423-424(2012)154-161 xylenes,ethylbenzene,trimethylbenzene,ethylmethyl benzene MicZSM-5* and indane. 4007 MicZSM-5 The results show the yield and product distribution are influ- MesZSM-5 enced to some degree by the concentration of aluminum in the MesZSM-5 sample.The optimum aluminum content of the ZSM-5 CFP catalyst 300 to maximize yield of aromatic hydrocarbons occurs at a SAR of 30. However,the relationship between aluminum content and selec- tivity for different aromatic species is less clear and other aspects of the ZSM-5 catalyst must be modified to control and improve the 200 product distribution. 3.2.Effects of mesoporosity and removal of external surface acid sites 100 The effects of mesoporosity and an acid treatment were inves- tigated to determine the roles of internal mass transfer rate and external-surface catalysis during CFP of biomass-derived 0 20 compounds.Samples of ZSM-5 were synthesized through a conven- 2日() tional TPA hydroxide method (MicZSM-5)and through a method using a combination of TPAand an organosilane surfactant to create Fig.3.X-ray diffraction patterns of mesoporous and conventional ZSM-5 catalysts crystalline ZSM-5 samples with hierarchical mesopores(MesZSM- before and after dealumination in L-tartaric acid.Mesoporous and purely micro- 5).All samples were synthesized with SiO2/Al2O3=30.Samples of porous samples synthesized were crystalline,and the ZSM-5 crystal structure is both materials were then treated with L-tartaric acid(MicZSM- retained after acid treatment. 5and MesZSM-5*)to selectively remove acid sites from external particle surfaces and to widen any existing mesopores [42]. Table 2 Microporous and mesoporous volume of the ZSM-5 samples used to investigate the X-ray diffraction measurements confirmed that both the con- effects of mesoporosity and dealumination treatment. ventional and hierarchical samples of ZSM-5 were crystalline (Fig.3)after the tartaric acid treatment.Acid treatment of the Sample Vmicro (cm3/g) Vmeso (cm2/g) mesoporous sample led to a decrease in intensity of the low angle MicZSM-5 0.118 0.054 peaks(20<10).suggesting some reduction in long-range crys- MicZSM-5* 0.122 0.062 MesZSM-5 0.107 0.550 talline order.This observation is consistent with the acid leaching of MesZSM-5 0.112 0.709 surface material leading to the expansion of intracrystalline meso- pores. SEM images were recorded for the mesoporous and purely Nitrogen adsorption on the MicZSM-5 resulted in a type I microporous samples (Fig.4).Significant structural differences isotherm characteristic of purely microporous material.A slight between MesZSM-5 and MicZSM-5 are clear.The primary parti- increase in the microporous volume was observed upon acid treat- cles comprising the mesoporous sample are much smaller than ment (MicZSM-5')of the non-mesoporous sample as seen in those observed for the purely microporous ZSM-5 sample.SEM Table 2,but the sample remained purely microporous.This result images of the samples after tartaric acid treatment showed no vis- shows that the acid treatment can be used to enhance existing ible decrease in particle size or roughening of particle surfaces. mesoporosity.but is not a means for creating mesoporosity by The characteristics of the pores within the zeolite particles itself.The adsorption isotherms show an increase in the measured were quantified using N2 physisorption.The tartaric acid treatment microporous volume of the samples after the dealuminating treat- was found to increase the average diameter of the mesopores in ment.The voids created by removal of aluminum from the ZSM-5 the mesoporous ZSM-5 sample.Fig.5 shows that the untreated framework likely account for this change. MesZSM-5 sample has pores 4-6nm in diameter,while after acid The extent of aluminum removal from particle surfaces was treatment(MesZSM-5)these pores expanded to 8-12nm.The quantified by XPS and the bulk composition of the zeolite samples total mesoporous volume of this material was also increased by the was measured using EDS (see Table 3).XPS measurements show acid treatment,and the microporous volume increased slightly. that acid treatment removed roughly 30%of the aluminum from Fig.4.SEM images of samples (A)MicZSM-5 and(B)MesZSM-5

158 A.J. Foster et al. / Applied Catalysis A: General 423–424 (2012) 154–161 xylenes, ethylbenzene, trimethylbenzene, ethylmethyl benzene, and indane. The results show the yield and product distribution are influ￾enced to some degree by the concentration of aluminum in the sample. The optimum aluminum content of the ZSM-5 CFP catalyst to maximize yield of aromatic hydrocarbons occurs at a SAR of 30. However, the relationship between aluminum content and selec￾tivity for different aromatic species is less clear and other aspects of the ZSM-5 catalyst must be modified to control and improve the product distribution. 3.2. Effects of mesoporosity and removal of external surface acid sites The effects of mesoporosity and an acid treatment were inves￾tigated to determine the roles of internal mass transfer rate and external-surface catalysis during CFP of biomass-derived compounds. Samples of ZSM-5 were synthesized through a conven￾tional TPA hydroxide method (MicZSM-5) and through a method using a combination of TPA and an organosilane surfactantto create crystalline ZSM-5 samples with hierarchical mesopores (MesZSM- 5). All samples were synthesized with SiO2/Al2O3 = 30. Samples of both materials were then treated with l-tartaric acid (MicZSM- 5* and MesZSM-5*) to selectively remove acid sites from external particle surfaces and to widen any existing mesopores [42]. X-ray diffraction measurements confirmed that both the con￾ventional and hierarchical samples of ZSM-5 were crystalline (Fig. 3) after the tartaric acid treatment. Acid treatment of the mesoporous sample led to a decrease in intensity of the low angle peaks (2 < 10◦), suggesting some reduction in long-range crys￾talline order. This observation is consistent with the acid leaching of surface material leading to the expansion of intracrystalline meso￾pores. SEM images were recorded for the mesoporous and purely microporous samples (Fig. 4). Significant structural differences between MesZSM-5 and MicZSM-5 are clear. The primary parti￾cles comprising the mesoporous sample are much smaller than those observed for the purely microporous ZSM-5 sample. SEM images of the samples after tartaric acid treatment showed no vis￾ible decrease in particle size or roughening of particle surfaces. The characteristics of the pores within the zeolite particles were quantified using N2 physisorption. The tartaric acid treatment was found to increase the average diameter of the mesopores in the mesoporous ZSM-5 sample. Fig. 5 shows that the untreated MesZSM-5 sample has pores 4–6 nm in diameter, while after acid treatment (MesZSM-5*) these pores expanded to 8–12 nm. The total mesoporous volume of this material was also increased by the acid treatment, and the microporous volume increased slightly. 0 10 20 30 40 50 0 100 200 300 400 MicZSM-5* MicZSM-5 MesZSM-5* MesZSM-5 Intensity (a.u.) 2Θ (º) Fig. 3. X-ray diffraction patterns of mesoporous and conventional ZSM-5 catalysts before and after dealumination in l-tartaric acid. Mesoporous and purely micro￾porous samples synthesized were crystalline, and the ZSM-5 crystal structure is retained after acid treatment. Table 2 Microporous and mesoporous volume of the ZSM-5 samples used to investigate the effects of mesoporosity and dealumination treatment. Sample Vmicro (cm3/g) Vmeso (cm3/g) MicZSM-5 0.118 0.054 MicZSM-5* 0.122 0.062 MesZSM-5 0.107 0.550 MesZSM-5* 0.112 0.709 Nitrogen adsorption on the MicZSM-5 resulted in a type I isotherm characteristic of purely microporous material. A slight increase in the microporous volume was observed upon acid treat￾ment (MicZSM-5*) of the non-mesoporous sample as seen in Table 2, but the sample remained purely microporous. This result shows that the acid treatment can be used to enhance existing mesoporosity, but is not a means for creating mesoporosity by itself. The adsorption isotherms show an increase in the measured microporous volume of the samples after the dealuminating treat￾ment. The voids created by removal of aluminum from the ZSM-5 framework likely account for this change. The extent of aluminum removal from particle surfaces was quantified by XPS and the bulk composition of the zeolite samples was measured using EDS (see Table 3). XPS measurements show that acid treatment removed roughly 30% of the aluminum from Fig. 4. SEM images of samples (A) MicZSM-5 and (B) MesZSM-5.

AJ.Foster et al.Applied Catalysis A:General 423-424(2012)154-161 159 MesZSM-5 600 -.MesZSM-5" 100 400 200 MicZSM-5 MicZSM-5* MesZSM-5 MesZSM-5 Fig.6.Comparison of the yield of aromatics from glucose pyrolysis over micro porous ZSM-5(MicZSM-5).tartaric acid-treated ZSM-5(MicZSM-5),mesoporous ZSM-5(MesZSM-5)and mesoporous ZSM-5 treated with tartaric acid(MesZSM-5"). Reaction conditions:600C.19 mg catalyst/mg glucose,and 240s reaction time. 0.0 0.2 04 0.6 0.8 1.0 P/P hierarchical mesopores did little to improve the yield of aromatic products from CFP.The yield of CO2 was increased slightly over the mesoporous samples.The removal of the acid sites from the sur- face sites and mesopore walls by dealumination had no significant 0.15 -MesZSM-5 ......MesZSM-5* effect on the extent of coke formation.This indicates that at these conditions,acid sites present on mesopore walls and external par- ticle surfaces do not promote coke formation over production of volatile aromatic species.Mesoporous ZSM-5 has been observed to promote coke formation faster than conventional ZSM-5 cata- 0.10 lysts in past studies of larch [43]and pine[44]sawdust pyrolysis on mesoporous ZSM-5 catalyst at 500C.In these studies,the pres- ence of mesoporosity allowed for the formation of larger aromatics which were able to polymerize into coke.However,at higher tem- 0.05 peratures these larger aromatics are more volatile and are better able to diffuse out of the mesopores of the sample.For this reason, only small differences were observed in the coke yield between mesoporous and purely microporous samples of ZSM-5. The most notable difference between mesoporous and purely 0.00+ microporous samples was the distribution of aromatic products. 0 10 20 Mesoporous ZSM-5 was more selective for the production of larger D(nm) aromatic species from glucose (Fig.8).The microporous mate- rials produced only a small amount of Cg and larger aromatics, Fig.5.Nitrogen adsorption isotherm and BIH pore size distribution of mesoporous ZSM-5 catalyst both before(solid line)and after(dashed)treatment with L-tartaric while this was dramatically increased over the mesoporous mate- acid. rial.Similar effects of mesoporosity on product selectivity have also been observed for xylene isomerization on a zeolite cata- the exterior particle surfaces in both cases.The EDS measurements lyst [45].Decreasing the diffusion length in a ZSM-5 catalyst has show no statistically significant change in the bulk composition also been shown to lead to larger products in the conversion of of the zeolite samples after the tartaric acid treatment.Taken propanal [46].The dealuminated mesoporous ZSM-5 sample was together,this indicates that the tartaric acid treatment is highly slightly more selective for larger hydrocarbons (C1o and polyaro- selective in leaching Bronsted acid sites from the particle surface matics)than the untreated mesoporous sample,suggesting that leaving the bulk composition of the zeolite unaffected.This treat- the mesopore diameter can influence the distribution of aromatics ment is also an effective means for increasing the mean mesopore diameter without significantly altering the chemical characteristics of the bulk ZSM-5. 100 3.2.1.Glucose and maple wood pyrolysis Figs.6 and 7 show the yield of different products from pyrol- 60 ysis of glucose and powdered maple wood,respectively,over the ZSM-5 catalysts.The removal of surface acid sites and creation of 40 Table 3 Surface(via XPS)and bulk(via EDS)composition of ZSM-5 samples before and after dealumination. Sample Surface SiOz/Al2O3 Bulk SiOz/Al2O MicZSM-5 MicZSM-5*MesZSM-5 MesZSM-5* As-synthesized Acid treated As-synthesized Acid treated Fig.7.Comparison of the yield of aromatics from maple wood pyrolysis over micro- MesZSM-5 34 48 2 45 porous ZSM-5(MicZSM-5).tartaric acid-treated ZSM-5(MicZSM-5*).mesoporous MicZSM-5 46 65 32 3 ZSM-5(MesZSM-5)and mesoporous ZSM-5 treated with tartaric acid(MesZSM-5). Reaction conditions:600C.19mg catalyst/mg wood,and 240s reaction time

A.J. Foster et al. / Applied Catalysis A: General 423–424 (2012) 154–161 159 0.0 0.2 0.4 0.6 0.8 1.0 0 200 400 600 Vads (cm3/g) P/Po MesZSM-5 MesZSM-5* 0 5 10 15 20 0.00 0.05 0.10 0.15 dV meso/dD (cm3/g*nm) D (nm) MesZSM-5 MesZSM-5* Fig. 5. Nitrogen adsorption isotherm and BJH pore size distribution of mesoporous ZSM-5 catalyst both before (solid line) and after (dashed) treatment with l-tartaric acid. the exterior particle surfaces in both cases. The EDS measurements show no statistically significant change in the bulk composition of the zeolite samples after the tartaric acid treatment. Taken together, this indicates that the tartaric acid treatment is highly selective in leaching Brønsted acid sites from the particle surface, leaving the bulk composition of the zeolite unaffected. This treat￾ment is also an effective means for increasing the mean mesopore diameter without significantly altering the chemical characteristics of the bulk ZSM-5. 3.2.1. Glucose and maple wood pyrolysis Figs. 6 and 7 show the yield of different products from pyrol￾ysis of glucose and powdered maple wood, respectively, over the ZSM-5 catalysts. The removal of surface acid sites and creation of Table 3 Surface (via XPS) and bulk (via EDS) composition of ZSM-5 samples before and after dealumination. Sample Surface SiO2/Al2O3 Bulk SiO2/Al2O3 As-synthesized Acid treated As-synthesized Acid treated MesZSM-5 34 48 42 45 MicZSM-5 46 65 32 31 MicZSM-5 MicZSM-5* MesZSM-5 MesZSM-5* 0 20 40 60 80 100 Carbon Yield (%) Unidentified Coke CO CO Aromatics Fig. 6. Comparison of the yield of aromatics from glucose pyrolysis over micro￾porous ZSM-5 (MicZSM-5), tartaric acid-treated ZSM-5 (MicZSM-5*), mesoporous ZSM-5 (MesZSM-5) and mesoporous ZSM-5 treated with tartaric acid (MesZSM-5*). Reaction conditions: 600 ◦C, 19 mg catalyst/mg glucose, and 240 s reaction time. hierarchical mesopores did little to improve the yield of aromatic products from CFP. The yield of CO2 was increased slightly over the mesoporous samples. The removal of the acid sites from the sur￾face sites and mesopore walls by dealumination had no significant effect on the extent of coke formation. This indicates that at these conditions, acid sites present on mesopore walls and external par￾ticle surfaces do not promote coke formation over production of volatile aromatic species. Mesoporous ZSM-5 has been observed to promote coke formation faster than conventional ZSM-5 cata￾lysts in past studies of larch [43] and pine [44] sawdust pyrolysis on mesoporous ZSM-5 catalyst at 500 ◦C. In these studies, the pres￾ence of mesoporosity allowed for the formation of larger aromatics which were able to polymerize into coke. However, at higher tem￾peratures these larger aromatics are more volatile and are better able to diffuse out of the mesopores of the sample. For this reason, only small differences were observed in the coke yield between mesoporous and purely microporous samples of ZSM-5. The most notable difference between mesoporous and purely microporous samples was the distribution of aromatic products. Mesoporous ZSM-5 was more selective for the production of larger aromatic species from glucose (Fig. 8). The microporous mate￾rials produced only a small amount of C9 and larger aromatics, while this was dramatically increased over the mesoporous mate￾rial. Similar effects of mesoporosity on product selectivity have also been observed for xylene isomerization on a zeolite cata￾lyst [45]. Decreasing the diffusion length in a ZSM-5 catalyst has also been shown to lead to larger products in the conversion of propanal [46]. The dealuminated mesoporous ZSM-5 sample was slightly more selective for larger hydrocarbons (C10 and polyaro￾matics) than the untreated mesoporous sample, suggesting that the mesopore diameter can influence the distribution of aromatics MicZSM-5 MicZSM-5* MesZSM-5 MesZSM-5* 0 20 40 60 80 100 Carbon Yield (%) Unidentified Coke CO CO Aromatics Fig. 7. Comparison of the yield of aromatics from maple wood pyrolysis over micro￾porous ZSM-5 (MicZSM-5), tartaric acid-treated ZSM-5 (MicZSM-5*), mesoporous ZSM-5 (MesZSM-5) and mesoporous ZSM-5 treated with tartaric acid (MesZSM-5*). Reaction conditions: 600 ◦C, 19 mg catalyst/mg wood, and 240 s reaction time

160 AjJ.Foster et aL Applied Catalysis A:General 423-424(2012)154-161 MicZSM-5 Table 4 ☒MicZSM-5* Furan conversion and product selectivity obtained from reaction over microporous and mesoporous ZSM-5 samples.Reaction conditions:600C,WHSV=10.4h-1,and ZZZ☑MesZSM-5 Pfuran=6Torr. ☒MesZSM-5 Sample Mic HZSM-5 Mic HZM-5*Mes HZSM-5 Mes HZSM-5 Furan conversion ( 35.9 403 36.3 29.5 Overall selectivity (% Aromatics 44.7 40.5 Olefins 192 172 8 CO 12.0 11 C02 2.7 Coke 174 48 器 器 5 Oxygenates 4.1 5.5 6.9 Aromatic selectivity( Benzene(C6) 21.0 20.7 18.3 178 Toluene(Cz) 18.6 Cs aromaticsb Ca aromaticse 8 留 Cio aromaticsd 订数1511功 Naphthalenes C6 C7 C8 C9 C10 Polyarom. Olefin selectivity ( Ethylene 36.4 36.6 26.7 26.8 Fig.8.Distribution of aromatic products from pyrolysis of glucose over microp- Propylene 348 38.1 34.8 orous ZSM-5 (MicZSM-5).tartaric acid-treated ZSM-5(MicZSM-5).mesoporous Allene 1 13.7 ZSM-5(MesZSM-5)and mesoporous ZSM-5 treated with tartaric acid(MesZSM-5*) Ca olefins 4.6 程 6> Reaction conditions:600C.19mg catalyst/mg glucose,and 240s reaction time. Cs olefins 12.5 11.7 11. 13品0 Ce olefins 3.5 3.6 5.6 6.6 Oxygenates include methylfuran,furylethylene,and benzofuran created through catalytic pyrolysis.Small differences were C8aromatics include ethylbenzene.styrene,and xylenes. observed between MicZSM-5 and the Zeolyst ZSM-5 with SAR=30 C9 aromatics include indene,indane,and methylstyrenes. used in the previous section.The total aromatic yield appears higher d Methylindene is the only C1o monoaromatic observed. for the Zeolyst sample,but the yield of monoaromatic compounds is nearly the same.Larger polyaromatic compounds account for the bulk of the difference in yield between these two samples.SEM from maple than the microporous samples.The volatile interme images showed different particle morphology for MicZSM-5(Fig.4) diate species formed during the initial thermal decomposition of and the Zeolyst sample(see supporting information),and the more wood are larger than those formed during pyrolysis of glucose, tightly packed MicZSM-5 particles may have been more effective at and these reactants naturally are less able to access the Bronsted acid sites in a purely microporous sample of ZSM-5.When this converting these polyaromatics to coke than the open aggregates of Zeolyst ZSM-5 particles. restriction on reactant diffusion is relaxed by incorporating meso- pores into the ZSM-5,these intermediate products are more likely The trends in aromatic distribution were largely the same dur- to crack into units that lead to monoaromatics inside the zeolite ing the pyrolysis of maple wood(Fig.9).Both mesoporous catalysts were more selective than the purely microporous samples for the rather than forming coke through a noncatalytic process outside production of Cg and larger aromatics.As with glucose,the larger of the zeolite.Mesoporous samples of ZSM-5 favor the production of larger alkylaromatics due to the relaxation of shape-selectivity mesopores in the dealuminated sample shifted the product distri- controlling the product distribution. bution towards C1o and larger polyaromatic products.However,the mesoporous samples were found to produce fewer polyaromatics 3.2.2.Furan conversion The micro-and mesoporous ZSM-5 catalysts were tested for MicZSM-5 conversion of furan in a continuous flow fixed-bed reactor to mea- MicZSM-5 sure the activity and selectivity of these different materials as 77788ZSM-5 shown in Table 4.We have previously shown that furan is an 35 8☒MesZSM-5* important intermediate during CFP of glucose [151.In addition,the enhancement of reactant diffusivity by mesoporous ZSM-5 could be 30 better observed in a fixed-bed reactor than the semi-batch reactor 25 Furan CFP had a slightly lower reaction rate over the mesoporous ZSM-5 samples than over the microporous samples at the condi- 20 tions tested.As observed for the CFP of glucose and maple wood, the mesoporous catalysts also produced more coke from furan.The mesoporous ZSM-5 samples had slightly lower yields of aromat- ics and olefins than the microporous ZSM-5.This suggests that the mesopores can act as spaces for the formation and accumulation of coke.The improved molecular diffusion in mesopores does not contribute positively to the total yield of aromatics from pyrol- ysis of furan.The mesoporous material had lower selectivity to C6 C8 C9 C10 Polyarom benzene,toluene and xylene,and tended to favor production of Fig.9.Distribution of aromatic products from pyrolysis of maple wood over micro- larger monoaromatics than the microporous materials.This was porous ZSM-5(MicZSM-5).tartaric acid-treated ZSM-5(MicZSM-5).mesoporous also observed for these catalysts during the conversion of glucose ZSM-5(MesZSM-5)and mesoporous ZSM-5 treated with tartaric acid (MesZSM-5*) and maple wood.CO and CO2 selectivity were similar for all cat- Reaction conditions:600C.19mg catalyst/mg wood,and 240s reaction time. alysts tested.Direct quantification of the water produced during

160 A.J. Foster et al. / Applied Catalysis A: General 423–424 (2012) 154–161 C6 C7 C8 C9 C10 Polyarom. 0 5 10 15 20 25 30 35 Aromatic Selectivity (%) MicZSM-5 MicZSM-5* MesZSM-5 MesZSM-5* Fig. 8. Distribution of aromatic products from pyrolysis of glucose over microp￾orous ZSM-5 (MicZSM-5), tartaric acid-treated ZSM-5 (MicZSM-5*), mesoporous ZSM-5 (MesZSM-5) and mesoporous ZSM-5 treated with tartaric acid (MesZSM-5*). Reaction conditions: 600 ◦C, 19 mg catalyst/mg glucose, and 240 s reaction time. created through catalytic pyrolysis. Small differences were observed between MicZSM-5 and the Zeolyst ZSM-5 with SAR = 30 usedintheprevious section. The total aromatic yieldappearshigher for the Zeolyst sample, but the yield of monoaromatic compounds is nearly the same. Larger polyaromatic compounds account for the bulk of the difference in yield between these two samples. SEM images showed different particle morphology for MicZSM-5 (Fig. 4) and the Zeolyst sample (see supporting information), and the more tightly packed MicZSM-5 particles may have been more effective at converting these polyaromatics to coke than the open aggregates of Zeolyst ZSM-5 particles. The trends in aromatic distribution were largely the same dur￾ing the pyrolysis of maple wood (Fig. 9). Both mesoporous catalysts were more selective than the purely microporous samples for the production of C8 and larger aromatics. As with glucose, the larger mesopores in the dealuminated sample shifted the product distri￾bution towards C10 and larger polyaromatic products. However,the mesoporous samples were found to produce fewer polyaromatics C6 C7 C8 C9 C10 Polyarom. 0 5 10 15 20 25 30 35 Aromatic Selectivity (%) MicZSM-5 MicZSM-5* MesZSM-5 MesZSM-5* Fig. 9. Distribution of aromatic products from pyrolysis of maple wood over micro￾porous ZSM-5 (MicZSM-5), tartaric acid-treated ZSM-5 (MicZSM-5*), mesoporous ZSM-5 (MesZSM-5) and mesoporous ZSM-5 treated with tartaric acid (MesZSM-5*). Reaction conditions: 600 ◦C, 19 mg catalyst/mg wood, and 240 s reaction time. Table 4 Furan conversion and product selectivity obtained from reaction over microporous and mesoporous ZSM-5 samples. Reaction conditions: 600 ◦C, WHSV= 10.4 h−1, and pfuran = 6 Torr. Sample Mic HZSM-5 Mic HZM-5* Mes HZSM-5 Mes HZSM-5* Furan conversion (%) 35.9 40.3 36.3 29.5 Overall selectivity (%) Aromatics 44.7 40.5 35.8 37.0 Olefins 19.2 17.2 17.1 16.3 CO 12.0 11.3 9.8 9.2 CO2 2.7 2.8 2.8 2.5 Coke 17.4 24.6 29.0 28.1 Oxygenatesa 4.1 3.7 5.5 6.9 Aromatic selectivity (%) Benzene (C6) 21.0 20.7 18.3 17.8 Toluene (C7) 18.6 18.1 17.7 18.2 C8 aromaticsb 8.8 8.1 8.7 8.7 C9 aromaticsc 13.9 14.2 16.5 15.7 C10 aromaticsd 7.4 8.3 11.7 12.8 Naphthalenes 30.4 30.6 27.1 26.7 Olefin selectivity (%) Ethylene 36.4 36.6 26.7 26.8 Propylene 34.8 34.5 38.1 34.8 Allene 8.2 8.4 11.8 13.7 C4 olefins 4.6 5.2 6.7 5.1 C5 olefins 12.5 11.7 11.1 13.0 C6 olefins 3.5 3.6 5.6 6.6 a Oxygenates include methylfuran, furylethylene, and benzofuran b C8 aromatics include ethylbenzene, styrene, and xylenes. c C9 aromatics include indene, indane, and methylstyrenes. d Methylindene is the only C10 monoaromatic observed. from maple than the microporous samples. The volatile interme￾diate species formed during the initial thermal decomposition of wood are larger than those formed during pyrolysis of glucose, and these reactants naturally are less able to access the Brønsted acid sites in a purely microporous sample of ZSM-5. When this restriction on reactant diffusion is relaxed by incorporating meso￾pores into the ZSM-5, these intermediate products are more likely to crack into units that lead to monoaromatics inside the zeolite rather than forming coke through a noncatalytic process outside of the zeolite. Mesoporous samples of ZSM-5 favor the production of larger alkylaromatics due to the relaxation of shape-selectivity controlling the product distribution. 3.2.2. Furan conversion The micro- and mesoporous ZSM-5 catalysts were tested for conversion of furan in a continuous flow fixed-bed reactor to mea￾sure the activity and selectivity of these different materials as shown in Table 4. We have previously shown that furan is an important intermediate during CFP of glucose [15]. In addition, the enhancement of reactant diffusivity bymesoporous ZSM-5 could be better observed in a fixed-bed reactor than the semi-batch reactor. Furan CFP had a slightly lower reaction rate over the mesoporous ZSM-5 samples than over the microporous samples at the condi￾tions tested. As observed for the CFP of glucose and maple wood, the mesoporous catalysts also produced more coke from furan. The mesoporous ZSM-5 samples had slightly lower yields of aromat￾ics and olefins than the microporous ZSM-5. This suggests that the mesopores can act as spaces for the formation and accumulation of coke. The improved molecular diffusion in mesopores does not contribute positively to the total yield of aromatics from pyrol￾ysis of furan. The mesoporous material had lower selectivity to benzene, toluene and xylene, and tended to favor production of larger monoaromatics than the microporous materials. This was also observed for these catalysts during the conversion of glucose and maple wood. CO and CO2 selectivity were similar for all cat￾alysts tested. Direct quantification of the water produced during

AJ.Foster et al./Applied Catalysis A:General 423-424(2012)154-161 161 CFP was not possible,but it can be approximated from the com- official views or policies,either expressed or implied,of the Defense position of the other reaction products.The identified reaction Advanced Research Projects Agency or the Department of Defense products,including coke,had an atomic composition of approxi- mately 4.5 mol C/mol O and 1.1 mol C/mol H,compared to the furan Appendix A.Supplementary data feed with 4.0mol C/mol O and 1.0 mol C/mol H.From this infor- mation,it can be calculated that approximately 0.1 mol H2O is Supplementary data associated with this article can be found,in produced per mole of furan reacted. the online version,at doi:10.1016/j.apcata.2012.02.030. Treatment of samples with tartaric acid to remove external surface acid sites does not seem to improve the CFP of furan to References hydrocarbons.Some minor differences in the aromatic yield and distribution were observed between dealuminated samples and 以S%n9A.9e9e52x1838880s898. the untreated parent materials.Furan conversion over MicZSM-5* [3]A.V.Bridgwater.Chemical Engineering lournal 91(2003)87-102. formed more coke than on MicZSM-5.However,this observation [4]F.Talebnia.D.Karakshev.I.Angelidaki.Bioresource Technology 101 (2010) 4744-4753. may be the result of the higher furan conversion on MicZSM-5.As [5]R.Hilten,R.Speir,J.Kastner,K.C.Das.Journal of Analyticaland Applied Pyrolysis more of the furan is reacted,the potential for secondary reactions 88(2010)30-38. to form coke also increases.Overall,the results from furan conver- [6]M.R.Jan,F.Jabeen,J.Shah,F.Mabood,Journal ofThermal Analysis and Calorime- ty101(2010)303-308. sion suggest that the role of external surface acid sites during the [7]H.T.Lin,M.S.Haung.J.W.Luo.L.H.Lin,C.M.Lee,K.L Ou,Fuel Processing Tech- CFP of biomass is not critical enough to impact the distribution of nology91(2010)1355-1363. observed aromatic products. [8]A.Demirbas,Energy Conversion and Management 50(2009)2782-2801. [9]T.R.Carlson,Y.T.Cheng.J Jae,G.W.Huber,Energy Environmental Science 4 (2011)145-161. 4.Conclusions [10]T.R.Carlson,I.Jae,G.W.Huber,ChemCatChem 1(2009)107-110. 11]TRCarlson.]Jae.Y.C.Lin.G.A.Tompsett.G.W.Huber.Journal of Catalysis 270 2010110-124. We have investigated the catalytic fast pyrolysis of glucose, [12]T.R.Carlson,G.A Tompsett,W.C.Conner,G.W.Huber.Topics in Catalysis 52 maple wood,and furan over different types of ZSM-5 catalyst.The (2009)241-252. aromatic yield from glucose CFP goes through a maximum as a [13]T.R.Carlson,T.P.Vispute,G.W.Huber,ChemSusChem 1(2008)397-400. 141 function of framework silica-to-alumina ratio with an optimum Y.T.Cheng.G.W.Huber.ACS Catalysis 1(2011)611-628. [15]J.Jae.G.A.Tompsett,A.J.Foster,K.D.Hammond,S.M.Auerbach.R.F.Lobo.G.W. at SAR=30.This composition also minimizes the amount of coke Huber.Journal of Catalysis 279(2011)257-268. formed during reaction.This suggests that tuning the acid concen- [16]J.Jae,G.A.Tompsett,Y.C.Lin,T.R.Carlson.J.Shen.T.Zhang.B.Yang.C.E.Wyman. W.C.Conner.G.W.Huber.Energy Environmental Science 3(2010)358-365. tration within the zeolite framework is necessary to obtain high [17]N.M.Al-Otaibi.G.Hutchings,Catalysis Letters 134(2010)191-195. aromatic yields. [18]A.Bhan.N.Delgass,Catalysis Reviews 50(2008)19-151. Creating hierarchical mesopores within the zeolite catalyst had 19] M.Bjorgen.S.Svelle.F.Joense .J.Nerlov S.Kolboe,F.Bonino,L.Palumbo.S. little effect on the aromatic yield from the semi-batch CFP of glu- Bordiga,U.Olsbye,Journal of Catalysis 249(2007)195-207. 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The results from this paper show that the concentration of acid [38]A.M.Azeez,D.Meier.J.Odermatt,T.Willner,Energy Fuels 24(2010) sites on the ZSM-5 catalyst and mesopores within the ZSM-5 can be 2078-2085. [39]D.Mores,J.Kornatowski,U.Olsbye,B.M.Weckhuysen,Chemistry:A European adjusted to tune the conversion of biomass-derived molecules over Journal17(2011)2874-2884. ZSM-5 catalysts.The presence of external surface acid sites plays [40]T.A.Peters.J.van der Tuin,C.Houssin.M.A.G.Vorstman,N.E.Benes,Z.A.E.P. only a small role,and may not be an important factor in designing Vroon.A.Holmen,Catalysis Today 104(2005)288-295. catalysts for biomass CFP. [41]J.Zhao.W.Guo.G.Liu,X.Zhang.L Wang.Fuel Processing Technology 91(2010) 1090-1097. [42]V.N.Shetti.J.Kim,R.Srivastava,M.Choi,R.Ryoo.Journal of Catalysis 254(2008) 296-303 Acknowledgements [43]K.H.Park.HJ.Park.J.Kim.R.Ryoo. 1K.Jeor J.Park.Y.-K.Park,Journal of Nanoscience and Nanotechnology 10(2010)355-359. This work was supported through funding from the Defense [44]HJ.Park.H.S.Heo.J.-K.Jeon,J.Kim,R.Ryoo.K.-E.Jeong.Y.-K.Park,Applied Advanced Research Projects Agency (Surf-cat:Catalysts for Pro- Catalysis B:Environmental 95(2010)365-373. duction of JP-8 range molecules from Lignocellulosic Biomass).The [45]C.Fernandez.I.Stan,J.-P.Gilson.K.Thomas,A.Vicente.A.Bonilla.J.Perez- Ramirez,Chemistry:A European Journal 16(2010)6224-6233. views,opinions,and/or findings contained in this article are those [46]T.Q.Hoang.X.Zhu,L.L Lobban,D.E.Resasco,RG.Mallinson,Catalysis Commu- of the author and should not be interpreted as representing the nications11(2010)977-981

A.J. Foster et al. / Applied Catalysis A: General 423–424 (2012) 154–161 161 CFP was not possible, but it can be approximated from the com￾position of the other reaction products. The identified reaction products, including coke, had an atomic composition of approxi￾mately 4.5 mol C/mol O and 1.1 mol C/mol H, compared to the furan feed with 4.0 mol C/mol O and 1.0 mol C/mol H. From this infor￾mation, it can be calculated that approximately 0.1 mol H2O is produced per mole of furan reacted. Treatment of samples with tartaric acid to remove external surface acid sites does not seem to improve the CFP of furan to hydrocarbons. Some minor differences in the aromatic yield and distribution were observed between dealuminated samples and the untreated parent materials. Furan conversion over MicZSM-5* formed more coke than on MicZSM-5. However, this observation may be the result of the higher furan conversion on MicZSM-5. As more of the furan is reacted, the potential for secondary reactions to form coke also increases. Overall, the results from furan conver￾sion suggest that the role of external surface acid sites during the CFP of biomass is not critical enough to impact the distribution of observed aromatic products. 4. Conclusions We have investigated the catalytic fast pyrolysis of glucose, maple wood, and furan over different types of ZSM-5 catalyst. The aromatic yield from glucose CFP goes through a maximum as a function of framework silica-to-alumina ratio with an optimum at SAR = 30. This composition also minimizes the amount of coke formed during reaction. This suggests that tuning the acid concen￾tration within the zeolite framework is necessary to obtain high aromatic yields. Creating hierarchical mesopores within the zeolite catalyst had little effect on the aromatic yield from the semi-batch CFP of glu￾cose and maple wood. Pyrolysis over mesoporous ZSM-5 catalysts yielded slightly more coke than the purely microporous samples. This suggests thatthe mesopores may act as spaces for coke to form and accumulate. The purely microporous ZSM-5 catalyst favors the production of smaller monoaromatics (benzene, toluene, and xylene) while hierarchically mesoporous samples shifts the prod￾uct distribution towards heavier alkylated monoaromatics. Similar observations were made in the CFP of furan in the fixed-bed reactor studies. Mesoporous catalysts tended to produce more coke and were more selective for the production of larger monoaromatic products than purely microporous ZSM-5. The reaction rate offuran over mesoporous ZSM-5 was also found to be slightly slower on mesoporous ZSM-5. The selective removal of external acid sites from the ZSM-5 cat￾alysts decreased the selectivity to the desired aromatic products and had little effect on the rate of furan conversion during CFP. The aromatic yield and selectivity from surface dealuminated sam￾ples were largely the same as the untreated parent material. This suggests that the presence of these external surface sites has only minor effects on the overall CFP chemistry. The results from this paper show that the concentration of acid sites on the ZSM-5 catalyst and mesopores within the ZSM-5 can be adjusted to tune the conversion of biomass-derived molecules over ZSM-5 catalysts. The presence of external surface acid sites plays only a small role, and may not be an important factor in designing catalysts for biomass CFP. Acknowledgements This work was supported through funding from the Defense Advanced Research Projects Agency (Surf-cat: Catalysts for Pro￾duction of JP-8 range molecules from Lignocellulosic Biomass). 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