Catalytic Fast Pyrolysis of Rice Straw to Aromatics over Hierarchical

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Biofuels and Biomass

Catalytic Fast Pyrolysis of Rice Straw to Aromatics over Hierarchical HZSM-5 Treated with Different Organosilanes Zihao Zhang, Hao Cheng, Hao Chen, Jing Li, Kequan Chen, Xiuyang Lu, Pingkai Ouyang, and Jie Fu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b03213 • Publication Date (Web): 12 Nov 2018 Downloaded from http://pubs.acs.org on November 14, 2018

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Catalytic Fast Pyrolysis of Rice Straw to Aromatics over Hierarchical HZSM-5 Treated with Different Organosilanes Zihao Zhanga, Hao Chenga,b, Hao Chena, Jing Lia, Kequan Chenb, Xiuyang Lua, Pingkai Ouyangb, Jie Fua* a

Key Laboratory of Biomass Chemical Engineering of Ministry of Education, College of

Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China b

State Key Laboratory of Materials-Oriented Chemical Engineering, College of

Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, Nanjing 211816, China

* Corresponding author Jie Fu, Tel: +86 571 87951065, E-mail address: [email protected]

Abstract: Hierarchical HZSM-5 with tunable acidity, zeolitic crystallinity and porosity were prepared using different organosilanes for catalytic fast pyrolysis (CFP) of rice straw. As the chain length of organosilanes changed, the composition of the products including aromatics and coke varied greatly. Additionally, the introduction of ammonium ion into organosilanes led to the lower yield of aromatics and higher yield of coke. Transmission electron microscopy (TEM), temperature-programmed desorption of NH3 (NH3-TPD), N2 adsorption-desorption (BET), and X-ray diffraction (XRD) were used to explore the

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influence of the morphological structure, acidity distribution, textural properties and crystallinity on the CFP of rice straw. The results indicated that the crystallinity, textural properties, and total acidity had a great influence on the synthesis of aromatics. Keywords: Catalytic fast pyrolysis; Rice straw; Aromatics; Hierarchical HZSM-5; Organosilanes.

1. Introduction Catalytic fast pyrolysis (CFP) is the most economically feasible way for the direct production of aromatics including benzene, toluene, and xylene, from abundant renewable lignocellulosic biomass. In the typical CFP process, aromatics can be produced over inexpensive zeolite catalysts from renewable biomass materials in a single reactor.1-3 Pyrolysis vapors are first produced by thermal decomposition of biomass feedstocks during this process, and these vapors diffuse into zeolite catalysts to generate aromatics, olefins and some by-products.4 A variety of zeolite samples have been studied, and the results have shown that ZSM-5 zeolite performed better on aromatics production for CFP of lignocellulosic biomass.2, 5-8 Although ZSM-5 displayed superior CFP activity for the biomass conversion, the CFP process always leads to the formation of large molecules, collectively referred to as carbon.5 The formation of carbon not only results in a decreased aromatic yield but also affects the catalytic performance of zeolites.9-11 In addition, the typical microporous


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structure of the ZSM-5 zeolites hinder the diffusion of reactants and intermediates into the active sites in the pores due to channel blocking, which leads to catalyst deactivation.12-14 The main challenge for CFP of biomass-based feedstocks is how to improve the yields of aromatics while minimizing coke formation on ZSM-5.15 The introduction of mesopores has been reported recently as an efficient technique to further enhance diffusion to achieve higher aromatics yield and lower coke yield.2 The desilication method is considered as an efficient means for introducing mesopores via the treatment of alkaline solutions, and used for CFP of lignocellulosic biomass.16-18 Li and co-workers19 reported that hierarchical ZSM-5 desilicated using a NaOH solution exhibited higher aromatic yields of 26.2-30.2% and a lower coke yield for the CFP of beech wood than those of blank ZSM-5. Qiao et al. reported an 38.2% aromatic yield from CFP of cellulose treated with 0.6 M Na2CO3.16 Hoff and co-workers discovered that desilication of ZSM-5 contributed to a higher aromatic yield of 27.9% for CFP of red oak than the blank ZSM-5 (23.9%).18 Similar results were also reported by Jia and co-workers.20 Another method for mesopores generation is the introduction of mesotemplating, e.g., with organosilanes, during the synthesis of ZSM-5. Guo and co-workers synthesized hierarchical ZSM-5 zeolites with organosilanes as templates; the resulting zeolites exhibited higher selectivity to ethylbenzene for the alkylation reaction of benzene and ethane than bare ZSM-5 zeolites.21 Recently, organosilane-assisted preparation of hierarchical ZSM-5 Zeolites was reported and exhibited good application prospects.22-26


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However, the application of these hierarchical ZSM-5 Zeolites on CFP of biomass-derived feedstocks is still in its infancy. Specifically, the effect of the introduction of different organosilanes into ZSM-5 Zeolites for the CFP of rice straw is not discussed. Herein, we report the hierarchical HZSM-5 Zeolites prepared using hydrothermal crystallization method with five organosilanes (different carbon chain lengths and ionic compositions) shown in Figure 1 (methyltrimethoxysilane, MTS; propyltrimethoxysilane, PTS;

octyltrimethoxysilane,

OTS;

hexadecyltrimethoxysilane,

HTS;

dimethylhexadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, TPHAC) as templates. Thereafter, the CFP of rice straw over synthesized modified HZSM-5 Zeolites was studied. The influence of the morphological structure, acidity distribution, textural properties and crystallinity for the product distribution was compared using a series of characterizations.

2. Materials and methods 2.1 Materials

Tetraethyl orthosilicate (>99%, TEOS), MTS (AR), PTS (AR), OTS (AR), HTS (≥85%), TPHAC (≥65%) and NaAlO2 (>99%) were purchased from Aladdin, Shanghai. Tetrapropylammonium hydroxide (AR, TPAOH) and NH4Cl (AR) were obtained from Sinopharm Chemical Reagent Co., Ltd. HZSM-5 catalyst was achieved from Nankai University Catalyst Co., Ltd. Rice straw was obtained from a farm in Henan, China. Prior to use, Soxhlet extraction using ethanol and toluene as solvents was performed, and then


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dried at 110 °C overnight.

2.2 Synthesis of the catalysts

All modified HZSM-5 catalysts were prepared using five templates according to the procedure published by Serrano and co-workers.27 These templates were MTS, PTS, OTS, HTS, and TPHAC. Initially, a certain amount of NaAlO2 were dissolved in deionized water at room temperature under magnetic stirring for 0.5 h, and TPAOH was then dissolved in the above solution for next 0.5 h. Thereafter, TEOS was added under magnetic stirring at 1000 r/min for another 360 min. The molar composition in the achieved solution was: 1 Al2O3: 30 SiO2: 6 TPAOH: 900 H2O. Additionally, template (the mole ratio of template to SiO2 was 0.05) was added to the above solution and pre-crystallized under reflux at 90 °C for 20 h. The obtained solution was crystallized for 3 days at 170 °C, and the resulting solid products were washed and filtered using deionized water for three times. The material was dried at 110 °C in a forced air oven overnight and suspended three times at 80 °C in a 1.0 mol/L NH4Cl aqueous solution for 8-12 h using ion exchange, followed by calcination at 550 °C for 6 h. The achieved samples were denoted as MTS, PTS, OTS, HTS and TPHAC. For example, the MTS sample was a modified HZSM-5 sample synthesized using MTS as the template.


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2.3 CFP experiments

The CFP of rice straw was studied in a Tandem μ-reactor system (Rx-3050 TR, Frontier Laboratories, Japan), as shown in Figure S1. The identification and quantification of the products was conducted in a GC (GC-MS, Agilent 7890 B-5977A MSD) linked with thermal conductivity detector (TCD), flame ionization detector (FID) and mass spectrometer simultaneously using ultra-alloy-5 capillary as a column. The furnace consists of two reactors (40 °C ~ 900 °C), and the joint between GC-MS and furnaces. This joint position was controlled at 300 °C for minimizing the condensation of products. For each experiment, 5 mg catalyst and rice straw with mass ratio of 20: 1 was mixed and injected into the furnaces at 600 °C. A liquid nitrogen bath was conducted to keep the pyrolysis vapors of volatile substances before they reached the column, resulting in good separation.

2.4 Analysis method

The CHN elemental analysis of rice straw was studied via an elemental analyzer (Vario Micro, Germany), and the mass fraction of C, H, N in treated rice straw are 37.4, 5.4 and 0.9% respectively. The proximate analysis of rice straw was performed by different methods. Fat content was detected by the national test standard method GB 5009.6–2016.28 The content of crude protein was determined via traditional kjeldahl method. Lignocellulosic and ash contents were obtained using the procedure of Van Soset.29 As a


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result, more than 80% components (cellulose, hemicellulose, lignin, crude protein, fat and ash) in rice straw were determined and shown in Table S1. Each experiment was performed three times to obtain the standard deviations of each test material to produce reliable data. The quantification of liquid products was carried out by injecting calibration standards of each compound into the furnace under the same operating condition. Quantitative analyses of gaseous products were conducted by external standard method with the TCD detector. Other products were quantitated by their calibration curves with a FID detector. The carbon contents in reactants and products were quantified using elemental analysis (Vario Micro). The product yield and selectivity for special aromatics was obtained using the following equations. The main unaccounted content included large molecular substances, which cannot be detected by GC as well as undetected coke on the sample cup. Moles of carbons in special product 100% Moles of carbon in rice straw Moles of carbons in the target aromatic Selectivity to aromatic products= 100% Moles of carbons in the total aromatics

Yield of product=


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3. Results and discussion 3.1 Characterizations

Figure 2 displays the XRD patterns of the MTS, PTS, OTS, HTS and TPHAC catalysts. All samples had diffraction peaks located at 6°-9° and 22.5°-25° (JCPDS 420024), which were exclusively attributed to a ZSM-5 zeolite containing a typical MFI structure.24 These results revealed that the nucleation and growth of the MFI structure did not stop after the introduction of organosilanes.30 However, there were significant differences in the intensities of diffraction peaks among all catalysts, indicating that crystallinity was affected by different mesopore templates. The relative crystallinity was determined from the total peak areas at both 6-9° and 22.5-25°.31 According to the calculated results, HTS had the highest relative crystallinity of 100% and TPHAC the lowest relative crystallinity of 77.3%. The relative crystallinities of MTS, PTS and OTS were similar (around 85%). The N2 adsorption-desorption isotherms and pore size distributions of MTS, PTS, OTS, HTS and TPHAC are shown in Figure 3. In Figure 3a, all of the samples indicated the adsorption of numerous N2 at very low pressure, which was ascribed to the presence of micropores. For the MTS and HTS samples, a small amount of uptake of N2 at high pressure was discovered compared to their large uptakes at low pressure, indicating that these samples were dominated by a microporous structure. An obviously greater adsorption


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of N2 at a relative pressure of 0.2 to 0.95 was observed over PTS and OTS, which was due to the adsorption of N2 on the external surface or capillary condensation into mesopores.30 Compared to other samples, the TPHAC sample had a remarkable type H3 hysteresis loop classified by IUPAC classification at a relative pressure of 0.7-0.95, which is known as a hierarchical porous structure. This type H3 loop displayed slit-shaped pores formed from aggregates of plate-like particles.32 The BJH pore size distribution was measured and the corresponding results are exhibited in Figure 3b. For the MTS and HTS samples, a small mesopore size distribution was discovered, further indicating that the samples were dominated by a microporous structure. The presence of mesoporosity in PTS and OTS was clearly demonstrated by the pore size distribution from 2 to 10 nm, and PTS and OTS exhibited a higher degree of mesoporosity than MTS and HTS. Compared to the other samples, TPHAC showed the highest mesoporosity according to the isotherms and pore size distribution results. The above results revealed the existence of a little mesopores in MTS and HTS, also confirmed by the TEM results. Table 1 summarizes the texture data for all samples. Both the external surface area and mesopore volume of the samples followed the order MTS, HTS < PTS, OTS < TPHAC, consistent with the N2 adsorption-desorption results. MTS and HTS had the lowest total surface area (SBET) and pore volume of mesopores (Vmeso), primarily owing to the very small mesopores produced in MTS and HTS. TPHAC had the highest surface area among these five samples, possibly owing to the generation of a large number of mesopores.14


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PTS had a higher surface area than OTS due to its higher micropore surface area. Therefore, the chain length of different organosilanes and addition of ammonium ions in organosilanes had a significant influence on the textural properties of the HZSM-5 catalysts. TEM images of MTS, PTS, OTS, HTS and TPHAC are shown in Figure 4. In Figure 4a, d, micropores in MTS and HTS are clearly visible and the crystallite structures of HTS are more complete. A few nanosize particles are visible on the surface of the larger HZSM5 zeolites, contributing to the formation of intercrystal porosity. For PTS and OTS in Figure 4b and 4c, the crystallite shape showed obvious differences compared to that of MTS and HTS. The PTS and OTS samples showed a large crystal achieved from the accumulation of small crystallite and grains. In addition, obvious irregular voids distributed randomly were found, suggesting the formation of rich mesopores in PTS and OTS. For TPHAC, a cloud-like amorphous phase was observed in Figure 4e, and a large number of mesopores are also visible in Figure 4f, in agreement with the BET results. The surface acidity of the catalysts was conducted using NH3-TPD, as shown in Figure 5. All samples showed only two peaks, indicating that two types of acidic sites exist. Desorption at low temperature from 80 °C to 280 °C refers to the weakly acidic sites from the desorption of NH3 on Lewis acid sites and desorption at high temperature from 280 °C to 600 °C represents strongly acidic sites from the desorption of NH3 on Brønsted acid sites.16 The peaks and areas were fitted by a Gaussian method, and the quantitative results were given in Table 2. The content of strong acidic sites was observed to be higher than


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that of weak acidic sites. The amount of weakly acidic sties of OTS and TPHAC was relatively low, and MTS exhibited the strongest weakly acidic sties. An obvious increase in strong acid was observed when HTS was chosen as the organosilane. In summary, the content of total acidic sites went down in the order HTS > MTS > PTS > TPHAC > OTS. The molar ratios of SiO2/Al2O3 were also determined from the XRF results, as shown in Table 2. The results suggested that molar ratio of SiO2/Al2O3 increased in the order MTS < HTS < OTS < TPHAC < PTS. These results indicated that the SiO2/Al2O3 ratio might be affected by the introduction of various organosilanes.

3.2 CFP of rice straw

The aromatics can be directly synthesized from biomass-derived rice straw by the multi-step CFP route. First, the reactant was thermally decomposed into oxygenates, which were the intermediates in the whole reaction process. Second, the obtained oxygenates diffused into the pores of ZSM-5 zeolites. Third, aromatics were produced in pores by multi-step reactions including decarboxylation, decarbonylation, dehydration and oligomerization.2,19 In this study, CFP performance over a series of HZSM-5 catalysts synthesized with different organosilanes are displayed in Figure 6. An experiment without catalyst was performed for comparison, and no aromatics were detected. The yield of aromatics and coke over various catalysts was compared, with 22.6% aromatics yield and 49.8% coke yield achieved over the MTS catalyst. With the increase in the length of the


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carbon chain in the organosilanes, the yield of aromatics first decreased to 19.7% (PTS) and 21.1% (OTS) and then increased to 25.6% (HTS). When TPHAC was used as the organosilane, the yield of aromatics decreased from 25.6% to 19.7%; by contrast, the yield of coke increased from 43.3% to 50.4%. The CFP activity of rice straw over unmodified HZSM-5 catalysts have been performed at the same operating conditions. The obtained yield of aromatics over unmodified HZSM-5 catalyst with different SiO2/Al2O3 ratios was 22.6%, 23% and 21.5% respectively, which was much lower than that over HTS catalyst.33 These results confirmed that HZSM-5 treated with different organosilanes was an efficient route to enhance the aromatics yield from CFP process. The main reason was that the modified HZSM-5 catalysts introduced appropriate mesopores into the blank HZSM-5, which enhanced the diffusion of reactant. In general, the carbon yields of coke and liquid products exhibited inverse trends, indicating that the production of coke and deoxygenated liquid products are competing pathways. The above results show that the chain length and amount of ammonium ions in organosilanes had a great effect on CFP of rice straw. Moreover, the introduction of ammonium ion into the organosilanes had a side effect regarding CFP of rice straw. The lengths of carbon chain in different organosilanes significantly affected the growth of ZSM-5, and then influenced the catalytic performance on the CFP of rice straw. When MTS was used as the template, a small mesopore size distribution are found due to too short chain length as a template. Also, only a small amount of mesopores was found, as a


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result, the yield of aromatics over MTS catalyst was similar with the blank HZSM-5. With the increase in chain length, a larger mesopore distributions over PTS and OTS could be clearly seen in Figure 3b. Additionally, mesopores located in the framework of HZSM-5 are also seen in TEM images. However, this hierarchical HZSM-5 shows a low degree of crystallinity, leaded to the decrease in the yield of aromatics. For HTS, the carbon chain length was enough long to adsorb more aluminosilicate precursors. These aluminosilicate precursors are finally converted to small HZSM-5 particles on the surface of intact zeolites in Figure 4d during secondary crystallization. Thereafter, the intercrystal pores are created between small HZSM-5 particles and intact zeolites, which introduces additional channels and retains high crystallinity. As a result, HTS exhibits best CFP performance. Additionally, the yields of gaseous products (CO and CO2) were relatively unchanged using different organosilanes as templates. The TEM and XRD results showed that the HTS samples had better relative crystallinity than the MTS, PTS, OTS and TPHAC catalysts. The BET results exhibited that the microporous structure of the HTS samples was complete, and intercrystal pores between small ZSM-5 particles and intact zeolites were discovered. NH3-TPD revealed that the acidity went down in the order HTS>MTS>PTS>OTS>TPHAC. Although hierarchical structures were also discovered for MTS, PTS, OTS and TPHAC, the decrease in the content of crystallinity and total acidity leaded to a lower aromatics yield. Therefore, we deduced that an integrated factor of good crystallinity, stronger acidity, and hierarchical


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structure in HTS contributed to the enhanced selectivity to aromatic compounds. The selectivity for the different aromatics compositions is summarized, as shown in Table 3. It was found that the total selectivity for main aromatics products (benzene, toluene, xylenes, methyl naphthalene, and naphthalene) was up to 60%. For HTS, the yields of almost 70% of theses aromatics were achieved.

4. Conclusions In this article, hierarchical HZSM-5 samples were prepared with various organosilanes as templates and used for the production of aromatics from CFP of rice straw. With the increasing length of the carbon chain of the organosilanes, a significant increase in the yield of aromatics and decrease in the yield of coke were discovered. In addition, the introduction of ammonium ions into the organosilanes had a side effect on the production of aromatics. The results showed good crystallinity and the formation of an intercrystal mesopore contributed to higher aromatics yield. The highest total acidity discovered in HTS gave the highest yield of aromatic compounds (25.6%) and the lowest yield of coke (43.3%).

Acknowledgments This work was supported by the Zhejiang Provincial Natural Science Foundation of China (No. LR17B060002), the National Natural Science Foundation of China (Nos. 21436007, 21676243, 21706228), and the Fundamental Research Funds for the Central Universities (No. 2018QNA4038).


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Improved catalytic performance of hierarchical ZSM-5 synthesized by desilication with surfactants. Micropor. Mesopor. Mat. 2013, 165, 148-157. (15) Zhang, H.; Cheng, Y. T.; Vispute, T. P.; Xiao, R.; Huber, G. W. Catalytic conversion of biomass-derived feedstocks into olefins and aromatics with ZSM-5: the hydrogen to carbon effective ratio. Energy Environ. Sci. 2011, 4, 2297-2307. (16) Qiao, K.; Shi, X.; Zhou, F.; Chen, H.; Fu, J.; Ma, H.; Huang, H. Catalytic fast pyrolysis of cellulose in a microreactor system using hierarchical zsm-5 zeolites treated with various alkalis. Appl. Catal. A-Gen. 2017, 547, 274-282. (17) Shao, S.; Zhang, H.; Heng, L.; Luo, M.; Xiao, R.; Shen, D. Catalytic conversion of biomass derivates over acid dealuminated ZSM-5. Ind. Eng. Chem. Res. 2014, 53, 1587115878. (18) Hoff, T. C.; Gardner, D. W.; Thilakaratne, R.; Proano-Aviles, J.; Brown, R. C. Tessonnier, J. P. Elucidating the effect of desilication on aluminum-rich ZSM-5 zeolite and its consequences on biomass catalytic fast pyrolysis. Appl. Catal. A-Gen. 2017, 529, 6878. (19) Li, J.; Li, X.; Zhou, G.; Wang, W.; Wang, C.; Komarneni, S.; Wang, Y. Catalytic fast pyrolysis of biomass with mesoporous ZSM-5 zeolites prepared by desilication with NaOH solutions. Appl. Catal. A-Gen. 2014, 470, 115-122. (20) Jia, L.; Raad, M.; Hamieh, S.; Toufaily, J.; Hamieh, T.; Bettahar, M.; Mauviel, G.; Tarrighi, M.; Pinard, L.; Dufour, A. Catalytic fast pyrolysis of biomass: superior selectivity


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of hierarchical zeolites to aromatics. Green Chem. 2017, 19, 5442-5459. (21) Guo, Y. P.; Wang, H. J.; Guo, Y. J.; Guo, L. H.; Chu, L. F.; Guo, C. X. Fabrication and characterization of hierarchical ZSM-5 zeolites by using organosilanes as additives. Chem. Eng. J. 2011, 166, 391-400. (22) Li, M.; Oduro, I. N.; Zhou, Y.; Huang, Y.; Fang, Y. Amphiphilic organosilane and seed assisted hierarchical ZSM-5 synthesis: Crystallization process and structure. Micropor. Mesopor. Mat. 2016, 221, 108-116. (23) Xue, Z.; Zhang, T.; Ma, J.; Miao, H.; Fan, W.; Zhang, Y.; Li, R. Accessibility and catalysis of acidic sites in hierarchical ZSM-5 prepared by silanization. Micropor. Mesopor. Mat. 2012, 151, 271-276. (24) Zhu, H.; Abou-Hamad, E.; Chen, Y.; Saih, Y.; Liu, W.; Samal, A. K.; Basset, J. M. Organosilane with gemini-type structure as the mesoporogen for the synthesis of the hierarchical porous ZSM-5 zeolite. Langmuir 2016, 32, 2085-2092. (25) Wen, D.; Liu, Q.; Fei, Z.; Yang, Y.; Zhang, Z.; Chen, X.; Tang, J.; Cui, M.; Qiao, X. Organosilane-assisted synthesis of hierarchical porous ZSM-5 zeolite as a durable catalyst for light-olefins production from chloromethane. Ind. Eng. Chem. Res. 2018, 57, 446-455. (26) Zhao, F.; Liu, D.; Wang, Y. Novel Mesoporous ZSM-5 Zeolite with Disparate Morphologies Synthesized by a Double Long-alkyl-chain Organosilane Template. Tenside Surfact. Det. 2017, 54, 27-31. (27) Serrano, D. P.; Aguado, J.; Escola, J. M.; Rodriguez, J. M.; Peral, A. Effect of the


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organic moiety nature on the synthesis of hierarchical ZSM-5 from silanized protozeolitic units. J. Mater. Chem. 2008, 18, 4210-4218. (28) Han, X.; Huang, Z. X.; Wang, S. F.; Chen, X. D.; Li, Q. F.; Xu, K. X.; Chen, D. New insights to improve resolution and reliability of Raman spectral analysis using higherdensity multiscale regression. Chemometr. Intell. Lab. 2017, 169, 110-115. (29) Van Soest, P. V.; Robertson, J. B.; Lewis, B. A. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 2017, 74, 3583-3597. (30) Zhang, Y.; Zhu, K.; Zhou, X.; Yuan, W. Synthesis of hierarchically porous ZSM-5 zeolites by steam-assisted crystallization of dry gels silanized with short-chain organosilanes. New J. Chem. 2014, 38, 5808-5816. (31) Chen, H.; Shi, X.; Liu, J.; Jie, K.; Zhang, Z.; Hu, X.; Zhu, Y.; Lu, X.; Fu, J.; Huang, H.; Dai, S. Controlled synthesis of hierarchical ZSM-5 for catalytic fast pyrolysis of cellulose to aromatics. J. Mater. Chem. A 2018, 6, 21178-21185. (32) Chai, S.; Wang, H.; Liang, Y.; Xu, B. Sustainable production of acrolein: Gas-phase dehydration of glycerol over Nb2O5 catalyst. J. Catal. 2007, 250, 342-349. (33) Chen, H.; Cheng, H.; Zhou, F.; Chen, K.; Qiao, K.; Lu, X.; Ouyang, P.; Fu, J. Catalytic fast pyrolysis of rice straw to aromatic compounds over hierarchical HZSM-5 produced by alkali treatment and metal-modification. J. Anal. Appl. Pyrol. 2018, 131, 76-84.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. Structural formulas of different organosilanes, including MTS, PTS, OTS, HTS and TPHAC


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AC

TPHAC HTS

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

OTS PTS

MTS

10

20

2

30

40

Figure 2. XRD patterns of MTS, PTS, OTS, HTS and TPHAC samples


50

Energy & Fuels

MTS PTS OTS HTS TPHAC

400

3

Quantity Asorbed (cm /g STP)

500

300 200 100 0 0.0

0.2

0.4 0.6 Relative Pressure (P/P0)

0.8

1.0

(a) MTS PTS OTS HTS TPHAC

1.0 3

dv/dlog(D) Pore Volume (cm /g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.8 0.6 0.4 0.2 0.0

0

10

20

30

40

50

60

70

Pore Diameter (nm)

(b) Figure 3. N2 adsorption-desorption isotherms a) and pore size distributions b) of MTS, PTS, OTS, HTS and TPHAC catalysts


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Energy & Fuels

(a)

(b)

(c)

(d)

(e)

(f)

Figure 4. TEM images of a) MTS, b) PTS, c) OTS, d) HTS, e-f) TPHAC at low and high magnification, respectively.


Energy & Fuels

350


300 250 TCD signal (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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200 150 100 50 0

100

200

300 400 o Temperature ( C)

500

600

Figure 5. NH3-TPD profiles of the MTS, PTS, OTS, HTS and TPHAC samples


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50 40

Yield (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels


30 20 10 0

Aromatics Olefins

CO

CO2

Figure 6. Production distribution of CFP over various catalysts


Coke

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Table 1. Textural properties of the MTS, PTS, OTS, HTS and TPHAC catalysts

[a]

Sample

SBET/m2·g-1[a]

Smicro/m2·g-1[b]

Sext/m2·g-1[c]

Vmicro/cm3·g-1[d]

Vmeso/cm3·g-1[e]

MTS

300

198

102

0.10

0.12

PTS

421

222

199

0.12

0.28

OTS

359

168

191

0.09

0.37

HTS

319

217

106

0.12

0.10

TPHAC

440

201

239

0.10

0.62

Determined by the Brunauer-Emmett-Teller (BET) equation.

[b-c] [d-e]

Calculated using a t-plot method. The total pore volume was calculated according to the adsorbed amount of N2 at p/p0=0.99.

Additionally, the mesopore volume was determined from the total pore volume by subtracting the micropore volume.


Page 27 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 2. Acidity properties and Si/Al ratios of the a) MTS, b) PTS, c) OTS, d) HTS and e) TPHAC samples Weak Samples

T (°C)

Strong

Acidity

T (°C)

(μmol/g)

Acidity

Total acidity

SiO2/Al2O3a

(μmol/g)

(μmol/g)

ratio

MTS

177

123.1

383

133.6

256.7

33.3

PTS

179

107.5

365

142.8

250.3

37.7

OTS

172

76.1

329

134.4

210.5

34.6

HTS

173

109.5

337

163.1

272.6

34.1

TPHAC

173

68.4

325

145.8

214.2

36.7

a Determined

from the XRF results


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Table 3. Selectivity for aromatic products over the a) MTS, b) PTS, c) OTS, d) HTS and e) TPHAC samples Selectivity (%) Samples

Other Benzene

Toluene

Xylene

Naphthalene

Methyl naphthalene aromatics

MTS

12.2

24.1

21.8

7.3

9.0

25.6

PTS

11.0

24.4

23.3

5.0

5.1

31.2

OTS

10.6

22.8

22.1

4.5

4.8

35.2

HTS

11.2

23.3

18.1

7.3

9.1

31.0

TPHAC

9.2

21.8

18.4

4.2

4.7

41.7


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Energy & Fuels

Catalytic Fast Pyrolysis of Rice Straw to Aromatics over Hierarchical HZSM-5 Treated with Different Organosilanes Zihao Zhanga, Hao Chenga,b, Hao Chena, Jing Lia Kequan Chenb, Xiuyang Lua, Pingkai Ouyangb, Jie Fua*


Catalytic Fast Pyrolysis of Rice Straw to Aromatics over Hierarchical

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