Microporous HZSM-5 Research Articles

Structural elucidation of Kraft lignin isolated from black liquor by the gradient acid precipitation and highly selective production of light aromatics by tandem catalytic pyrolysis over dual-catalysts

Kraft lignin (KL), isolated from black liquor, serves as a significant feedstock for the production of bio-aromatics by catalytic fast pyrolysis (CFP). First, the influence of pH on the chemical structure of KL isolated by the gradient acid precipitation (GAP) was investigated. Then, the dual-catalyst CFP (DC-CFP) was employed to convert KL into light aromatics by using the hierarchical Nb2O5 (Hie-Nb2O5) and the microporous HZSM-5 as catalyst. Results showed that the decrease of pH during GAP promoted the breakage of the ether bond of KL, resulting in lower molecular weight and less content of hydroxyl group in KL. Among the four types of metal oxides (Hie-Nb2O5, Al2O3, MgO, and CaO), the synergistic effect of dual-catalyst grouped by Hie-Nb2O5 and HZSM-5 was best for the production of light aromatics. In addition, the maximum production of light aromatics was reached at the pH of 2 and the mass ratio of Hie-Nb2O5-to-HZSM-5 at 2:2.

Recovery of Kraft lignin from industrial black liquor for a sustainable production of value-added light aromatics by the tandem catalytic pyrolysis

Lignin, isolated from black liquor, is an important feedstock to produce bio-aromatics through catalytic fast pyrolysis. First, the variation in chemical structure among the Kraft lignin precipitated by the organic acids (acetic acid and citric acid) and the inorganic acids (hydrochloric acid and sulfuric acid) was investigated. Then, a sustainable production approach of light aromatics from Kraft lignin was developed, namely the dual-catalyst catalytic fast pyrolysis (DC-CFP) by using the mesoporous Nb2O5 and microporous HZSM-5 as catalyst. Results showed that the molecular weight of lignin isolated by inorganic acids (1674–1841 g/mol) was much lower than that of lignin isolated by organic acids (2040–2441 g/mol), caused by the fact that inorganic acids promoted the breakage of ether bonds in lignin. In addition, compared with lignin precipitated by the organic acids, the CFP of lignin precipitated by the inorganic acids has a higher yield of light aromatics, especially the lignin precipitated by the hydrochloric acid, reaching 1.39 × 108 a. u./mg. Among the different layout modes of catalyst, Model II (Meso-Nb2O5 blended with lignin, HZSM-5 placed separately from lignin) presented highest yield of light aromatics during DC-CFP of lignin, reaching 1.78 × 108 a. u./mg.

Catalytic upgrading of bio-oil model mixtures in the presence of microporous HZSM-5 and γ-Al2O3 based Ni, Ta and Zr catalysts

Bio-fuel production from bio-oil was investigated in the presence of microporous HZSM-5 and Al2O3 (MA) based catalysts. This study focused on the catalytic upgrading of a model bio-oil compound with ethanol for bio-fuel production. The model compound containing hydroxypropanol/furfural/formic acid: 4/6.5/5 by volume was used as a bio-oil mixture. Activity tests were performed under atmospheric pressure with a volumetric feed ratio of 30/70 bio-oil mixture/ethanol using a 0.5 g catalyst. In the reaction studies performed on the commercial microporous HZSM-5 catalyst, the optimum co-cracking temperature was determined as 400 °C. Mesoporous γ-Al2O3 support was synthesized by the evaporation-induced self-assembly (EISA) synthesis method, and Ni, Ta, and Zr metals were incorporated into the structure of the catalyst by the impregnation method to improve the surface acidity. The synthesized catalysts were characterized by X-ray diffraction (XRD), X-ray absorption near edge spectroscopy (XANES), N2 adsorption–desorption, scanning electron microscopy energy dispersive spectroscopy (SEM/EDS), X-ray fluorescence (XRF), Fourier-transformed infrared spectroscopy (FTIR), pyridine adsorbed diffuse reflectance FTIR spectroscopy (DRIFTS), and thermogravimetric/differential thermal analysis (TGA-DTA). Monometallic and pure alumina catalysts indicated an ordered mesoporous structure with surface area values 106–389 m2/g. Lewis and Brønsted acid sites associated with mild acidity were observed in the DRIFTS results of the 10 wt% Zr-containing alumina catalyst (10Zr@MA). The highest oil phase selectivity and isoparaffin selectivity in oil phase values were obtained in the presence of 10Zr@MA as 17.22% and 80.96%, respectively. 10Zr@MA catalyst showed the best catalytic activity compared to other catalysts, with 9.54% coke formation.

Catalytic pyrolysis of microalgal lipids to liquid biofuels: Metal oxide doped catalysts with hierarchically porous structure and their performance

Catalytic pyrolysis of lipids is an alternative pathway for alternative aviation fuel production with advantages of H2-free and mild reaction conditions. However, it is still hindered by coking of catalysts and low selectivity of kerosene. In this research, composite catalysts were synthesized via postsynthesis method (alkali treatment) followed by doping of metal oxides (ZnO, La2O3, and CeO2). Catalytic performance of as-synthesized catalysts was evaluated during catalytic pyrolysis of microalgal lipids. The characterization of BET, XRD, SEM, NH3-TPD for catalysts indicated that alkaline treatment increased the mesoporous structure (5.28–5.91 nm) of microporous zeolite HZSM-5 to form a hierarchically porous structure without apparent disruption of crystal structure of zeolite, while doping of metal oxides (about 10 wt%) enhanced the performance of hetero-atoms (oxygen and nitrogen) removal. The acidity of as-synthesized catalysts significantly decreased from 1175.61 μmol/g (HZSM-5) to 406.77 μmol/g (Ce-MHZ). After catalytic pyrolysis carbon number distribution and compound type of produced liquid fuels tended to high kerosene components (above 40%) and increased hydrocarbon content with reduced content of oxygen-containing compounds. The hierarchically porous zeolite also presented aromatization for aromatic hydrocarbons in alternative aviation fuels. Catalytic mechanism was also elucidated including complex reactions of decarboxylation, decarbonylation, carbon chain cracking, and aromatization.

Construction of mesoporous Ru@ZSM-5 catalyst for dichloromethane degradation: Synergy between acidic sites and redox centres

Ruthenium supported on hierarchical pore HZSM-5 zeolite (named Ru@mZ5) as an efficient catalyst for dichloromethane (DCM) oxidation was synthesized in this work. Ru component was introduced without the expense of acid site thanks to the more accessibility of mesopores. Instead, moderate Lewis acid (Ruδ+) that increased the surface acidity formed on the hierarchical pores. Ru@mZ5 also showed enhanced chemisorption and oxidation of DCM due to the synergy between the acidic properties and the ruthenium active centres. Compared with the bare microporous HZSM-5 (Ru/Z5) and mesoporous KIT-6 (Ru@K6) loaded Ru, the reaction rate of Ru@mZ5 was the highest at 200℃ (0.167 mmol/g h), the TOFRu was 0.0488 s−1, and the adsorption capacity of DCM was the highest at 50℃ (223 μmol/g) (600 ppm DCM, GHSV = 25,000 mL/g h). Moreover, the hierarchical pore structure of Ru@mZ5 were conducive to the desorption of products, which improved the reusability and stability of the catalyst under wet and dry conditions without chlorination byproducts.

Comparative effects of mesopores and framework defects on the deactivation of HZSM-5 catalyst during alkylphenol dealkylation

The dealkylation of alkylphenols over HZSM-5 is regarded as a promising way for the production of phenol from both fossilized and raw lignocellulose-derived oils. However, the pure microporous HZSM-5 deactivates fast due to coking. Although the introduction of mesopores into microporous HZSM-5 can enhance the catalyst stability, the relationship between the catalytic performance and changed properties caused by alkaline treatment remains ambiguous. In this study, the coke analysis reveals that the mesopore introduction primarily promotes the formation of external coke by providing additional diffusion paths for coke precursors. However, the phenolates bound to the Lewis acid sites generated on external surface facilitates the deposition of external coke, the total coke amount is thus not significantly impacted. Furthermore, the reduction of internal silanols (Si-related framework defects) and Lewis acid sites (Al-related framework defects) by ammonium hexafluorosilicate treatment declines the total amount of coke and alleviates catalyst deactivation.

Adsorbate/adsorbent interactions in microporous zeolites: mechanistic insights from NMR relaxation and DFT calculations

Nuclear magnetic resonance (NMR) relaxation is an effective and non-invasive technique for probing guest-host interactions in porous materials. In particular, the ratio of longitudinal-to-transverse nuclear spin relaxation time constants T1/T2 has been demonstrated as a robust indicator of adsorbate/adsorbent interactions in mesoporous media. However, the use of NMR relaxation times in microporous materials to probe interactions and dynamics remains relatively unexplored. Herein, we investigate and describe the effect of the aluminium content in microporous HZSM-5 zeolites on the NMR relaxation times of a range of common liquid probe molecules. In particular, we discuss the NMR relaxation time behavior of liquids with hydrophilic (water, methanol) and hydrophobic (toluene, methyl cyclohexane) properties adsorbed over HZSM-5 samples with varying silica-to-alumina ratios (SAR = SiO2/Al2O3). Our results demonstrate that highly polar molecules show high sensitivity to aluminium content (i.e., surface acidity), with T1/T2 ratios increasing significantly for higher acidity zeolites. Conversely, for molecules with low polarity, the T1/T2 ratio as a function of SAR remains approximately constant, and in the zeolites with low SAR is much lower compared to that of water and methanol. Density functional theory (DFT) calculations are employed to contrast the surface interaction mechanisms of water and toluene within model zeolite structures of varying SAR, and provide molecular level insights into the observed trends in NMR relaxation behavior.

Tailoring the impact of synthetic strategies on the catalytic upgrading of crude glycerol to produce bio-based aromatics in hierarchical HZSM-5

The catalytic upgrading of renewable biomass derived crude glycerol to generate bio-based aromatics is a promising alternative to petroleum route for the synthesis of valuable and versatile aromatics. The effects of synthetic strategies on the physicochemical property of hierarchical HZSM-5 as well as their corresponding catalytic upgrading performances of crude glycerol to bio-based aromatics were systematically investigated in this work. HZSM-5/0.3M NaOH catalyst exhibited smaller improvement in aromatic yields than microporous HZSM-5, which could be ascribed to the uncontrollable large intra-mesopore diameter and less increment in the amounts of acid sites during the introduction of mesoporosity via destructive alkali treatment. The soft templated HZSM-5/TPOAC catalyst produced more BTX and C9+ monocyclic aromatics, which could be attributed to its larger crystal sizes, higher external surfaces, luxuriant L acid amounts, uniform and small mesopore sizes. However, the hard templated HZSM-5/CNT-OH catalyst exhibited higher yields of polycyclic aromatic hydrocarbons and coke during the crude glycerol upgrading process, which could be assigned to its smaller crystal sizes, abundant B acid quantities, uniform and large mesopore diameters. The reusability of desilicated HZSM-5/0.3M NaOH was also deteriorated than the templated HZSM-5/CNT-OH and HZSM-5/TPOAC due to the inferior stability of incorporated mesoporosity via desilication. Finally, plausible reaction pathway involved catalytic upgrading of crude glycerol to produce aromatics was proposed in detail.

Enhanced catalytic performance of the hollow Mo/HZSM-5 nanocrystal for methane dehydroaromatization

Although Mo/HZSM-5 catalyst is widely used in the methane dehydroaromatization (MDA) reaction, the conventional microporous HZSM-5 with long diffusion path often causes the blockage of channels and pores by coke. In this work, a series of hollow HZSM-5 zeolites with different cavity sizes and tunable shell thickness were prepared by varying the alkali treatment time. After being loaded with Mo, the catalytic performances of the hollow catalysts were investigated in MDA reaction. Compared with conventional solid Mo/Z5 catalyst, the hollow Mo/Z5(x) catalysts exhibit higher CH4 conversion and C6H6 selectivity, which show an increasing trend with the increase of inner cavity size and decrease of zeolite shell thickness. Specifically, the hollow Mo/Z5(24) catalyst achieves the maximum CH4 conversion of 13.8% and C6H6 selectivity of 72%. It suggests that the hollow structure is conducive to enhance the accessibility of feed or intermediates to the Brønsted acid sites within zeolites and facilitates the rapid diffusion of the C6H6 from the intraframework channels rather than further polymerization to the coke. Furthermore, this novel structure endows stronger interaction between the Mo species and the acid sites, resisting agglomeration of Mo-species on external zeolite surface at high temperature. This research provides a new insight into exploiting a candidate catalyst for the MDA reaction.

A study on the production and engine analysis of organic liquid fuel from jatropha and castor oil by catalytic cracking over solid acid catalysts

Catalytic cracking of non-edible oils such as jatropha and castor was done in fixed bed catalytic reactor. The microporous catalysts such as Hβ, HY and HZSM-5 and mesoporous catalyst like AlMCM-41 were synthesised and characterised by XRD and BET surface area analyzer. The reaction parameters such as temperature of reaction, WHSV (Weight hourly space velocity) and reaction time were optimised over Hβ catalyst using jatropha oil. Organic liquid products (OLP) comprising of green gasoline (GG), green kerosene (GK) and green diesel (GD) and gaseous products were found to be major products. The liquid products were analysed using gas chromatograph (Shimadzu GC-9A) fitted with Apeizon-L packed column and gaseous products were analysed using Poropak Q column. The % conversion, yield of OLP and selectivity towards GG, GK and GD were found to be higher at temperature of 400 °C, WHSV of 4.8 h−1 and reaction time of 1 h. The cracking of jatropha oil was done over HY, HZSM-5 and AlMCM-41 at this optimised condition. Among the microporous materials HZSM-5 produced more OLP with more selectivity towards GG fraction (50%) but yielded higher % of gaseous products. While AlMCM-41 (Si/Al = 25) was selective towards middle distillates fraction like GK (45%) & GD (35%) and yielded low gaseous products. The mechanism of reaction proceeds via carbocation formation. The activity of HZSM-5 and AlMCM-41 were examined with castor oil. The OLP viability as a replacement fuel in a single-cylinder diesel engine under various loads was evaluated in an IC engine test. Here, we look at how different engine operating conditions affect fuel efficiency, Brake Thermal Efficiency (BTE), and emissions of Carbon Monoxide (CO), Carbon-di-oxide (CO2) and Nitrogen Oxide (NOx). Overall analysis indicates that OLP cracked from Jatropha oil serves as a best fuel in comparison with OLP obtained from Castor oil.

A Review of Recent Research on Catalytic Biomass Pyrolysis and Low-Pressure Hydropyrolysis

Direct catalytic upgrading of biomass-derived fast pyrolysis vapors can occur in different process configurations, under either inert or hydrogen-containing atmospheres. This review summarizes the myriad of different catalysts studied and benchmarks their deoxygenation performance by also taking into account the resulting decrease in bio-oil yield compared to a thermal pyrolysis oil. Generally, catalyst modifications aim at improving the initial selectivity of the catalyst to more desirable oxygen-free hydrocarbons and/or improving the catalysts’ stability against deactivation by coking. Optimizing the pore structure and acid site density/distribution of solid acid catalysts can slow down deactivation and prolong activity. Basic catalysts such as MgO and Na2O/γ-Al2O3 are excellent ketonization catalysts favoring oxygen removal via decarboxylation, whereas solid acid catalysts such as zeolites primarily favor decarbonylation and dehydration. Basic catalysts can therefore produce bio-oils with higher H/C ratios. However, since their coke formation per surface area is higher, compared to a microporous HZSM-5 zeolite, precoking (or imperfect regeneration) of these basic catalysts and operating for longer time-on-stream can be approaches to improve the oil yield. In-line vapor-phase upgrading with a dual bed comprising a solid acid catalyst followed by a basic catalyst active in ketonization and aldol condensation further improves deoxygenation while maintaining high bio-oil carbon recovery. Also low-cost catalysts such as iron-rich red mud have deoxygenation activity. An improved bio-oil carbon recovery─compared at a similar level of oxygen removal─can be obtained when changing from an inert atmosphere to a hydrogen-containing atmosphere and using an effective hydrodeoxygenation (HDO) catalyst. To keep costs low, this can be conducted at near-atmospheric pressure conditions. Pt/TiO2 and MoO3/TiO2 showed high activity and reduced coke formation. Stable performance has been demonstrated using Pt/TiO2 for 100+ reaction/regeneration cycles with woody biomass feedstock. If future works can demonstrate the same durability for lower-cost biomass containing higher contents of ash, N, and S, this would considerably boost the commercial viability of near-atmospheric pressure HDO. Further research should be directed to testing the durability of lower-cost HDO catalysts such as MoO3/TiO2 and further improving the activity and stability of lower-cost catalysts.

Catalytic Pyrolysis of Seawater Aged Polypropylene Over HZSM-5, HY, and Al-MCM-41.

The effect of seawater aging on the thermal and catalytic pyrolysis of polypropylene (PP) was investigated using a thermogravimetric analyzer and pyrolyzer-gas chromatography/mass spectrometry. Although the surface properties of PP were of the oxidized form by seawater aging, the decomposition temperature and non-catalytic pyrolysis products of PP were relatively unchanged largely due to seawater aging. The catalytic pyrolysis of seawater-aged PP over all the catalysts produced smaller amounts of aromatic hydrocarbons than that of fresh PP due to catalyst poisoning caused by the residual inorganics. Among the catalysts, microporous HZSM-5 (SiO₂/Al₂O₃:23) produced the largest amount of aromatic hydrocarbons followed in order by microporous HY(30) and nanoporous Al-MCM-41(20) from seawater-aged PP due to the high acidity and appropriate pore size for the generation of aromatic hydrocarbons.

ZnAlMCM-41: a very ecofriendly and reusable solid acid catalyst for the highly selective synthesis of 1,3-dioxanes by the Prins cyclization of olefins.

The Prins cyclization of styrene (SE) with paraformaldehyde (PFCHO) was conducted with mesoporous ZnAlMCM-41 catalysts for the synthesis of 4-phenyl-1,3-dioxane (4-PDO) using a liquid phase heterogeneous catalytic method. For a comparison study, the Prins cyclization reaction was also conducted over different nanoporous catalysts, e.g. mesoporous solid acid catalysts, AlMCM-41(21) and ZnMCM-41(21), and microporous catalysts, USY, Hβ, HZSM-5, and H-mordenite. The recyclable mesoporous ZnAlMCM-41 catalysts were reused in this reaction to evaluate their catalytic stabilities. Since ZnAlMCM-41(75) has higher catalytic activity than other solid acid catalysts, washed ZnAlMCM-41(75)/W-ZnAlMCM-41(75) was prepared using an efficient chemical treatment method and used with various reaction parameters to find an optimal parameter for the highly selective synthesis of 4-PDO. W-ZnAlMCM-41(75) was also used in the Prins cyclization of olefins with PFCHO and formalin (FN, 37% aqueous solution of formaldehyde (FCHO)) under different reaction conditions to obtain 1,3-dioxanes, which are widely used as solvents or intermediates in organic synthesis. Based on the nature of catalysts used under different reaction conditions, a reasonable plausible reaction mechanism for the Prins cyclization of SE with PFCHO is proposed. Notably, it can be seen from the catalytic results of all catalysts that the W-ZnAlMCM-41(75) catalyst has higher 4-PDO selectivity with exceptional catalytic activity than other microporous and mesoporous catalysts.

Nuclear spin relaxation as a probe of zeolite acidity: a combined NMR and TPD investigation of pyridine in HZSM-5.

The relative surface affinities of pyridine within microporous HZSM-5 zeolites are explored using two-dimensional 1H nuclear magnetic resonance (NMR) relaxation time measurements. The dimensionless ratio of longitudinal-to-transverse nuclear spin relaxation times T1/T2 is shown to exhibit strong sensitivity to the silica/alumina ratio (SAR) of these zeolites, which is indicative of material acidity. This trend is interpreted in terms of increased pyridine surface affinity with decreasing SAR. Temperature programmed desorption (TPD) analysis corroborates this observation, revealing a distinct increase in the heat of desorption associated with adsorbed pyridine as a function of decreasing SAR. A direct correlation between NMR and TPD data suggests NMR relaxation time analysis can be a valuable tool for the non-invasive characterisation of adsorption phenomena in microporous solids.

Effect of support nature on catalytic activity of the bimetallic RuCo nanoparticles for the oxidative removal of 1,2-dichloroethane

The nature of porous support (mesoporous Al2O3 and MgO (denoted as meso-Al2O3 and meso-MgO, respectively) and microporous HZSM-5) on catalytic performance of the bimetallic RuCo nanoparticles (NPs) was investigated for the oxidation of 1,2-dichloroethane (1,2-DCE). Redox and acid properties and reaction intermediates of the samples were measured by means of various techniques. The RuO2 species were dominantly present in the supported bimetallic samples, and Co doping could increase the length of the Ru−O bond. Compared with RuCo/meso-MgO and RuCo/meso-Al2O3, RuCo/HZSM-5 exhibited the highest catalytic activity (T90% =281 °C, TOFNoble metal = 3.6 × 10−3 s−1, reaction rate at 270 °C = 18.7 μmol/(gNoble metal s), and apparent activation energy =36 kJ/mol at SV = 20,000 mL/(g h)) and the best Cl-resistant performance, which was associated with its strong redox ability, suitable acidity, good 1,2-DCE adsorption capacity, highly dispersed RuCo NPs, and strong interaction between RuCo NPs and HZSM-5. Loading of RuCo NPs on the support could suppress the formation of C2H3Cl and improve the Cl-resistant performance. Over the RuCo/HZSM-5 sample, the partial deactivation induced by water vapor or HCl addition was reversible, while that induced by SO2 introduction was irreversible. Based on the characterization results, we believe that the oxidation of 1,2-DCE over RuCo/meso-Al2O3, RuCo/meso-MgO or RuCo/HZSM-5 might take place concurrently via the Langmuir−Hinshelwood and Mars−van Krevelen mechanisms. This work can provide a strategy to develop the efficient catalysts with low Cl-containing by-products formation, high CO2 selectivity, and good Cl-resistance in the oxidative removal of Cl-VOCs under the practical conditions.

Light olefin production using the mixture of HZSM-5/MCM-41 and γ-Al2O3 as catalysts for catalytic pyrolysis of waste tires

In this paper, micro-mesoporous HZSM-5/MCM-41 zeolites were prepared by a two-step hydrothermal method using commercial HZSM-5 with two different silica/alumina ratios (38 and 50) as starting materials. The structures, morphologies and acidity of as-prepared zeolites were analyzed using XRD, FT-IR, SEM, N2-adsorption/desorption and NH3-TPD. The HZSM-5/MCM-41 zeolites combined the acidity of microporous HZSM-5 with the pore advantages of mesoporous MCM-41. Mesopores and microspores of 3.34 and 0.95 nm in diameter were found to be present in HZSM-5/MCM-41 zeolites. When they were used to catalyze the pyrolysis of waste tires, the selectivity of light olefins for HZSM-5/MCM-41 prepared using HZSM-5 with the silica/alumina ratio of 50 as starting materials was 21.42%, higher than 18.43% of HZSM-5/MCM-41 synthesized using HZSM-5 with the silica/alumina ratio of 38. In order to further overcome the pore size constraints and mass transfer limitations of HZSM- -5/MCM-41 zeolites for catalyzing pyrolysis of waste tires, macroporous ?-Al2O3 were mixed with HZSM-5/MCM-41 and used as catalysts. The selectivity to light olefins for the mixture of ?-Al2O3 and HZSM-5/MCM-41 prepared using HZSM-5 with the silica/alumina ratio of 50 as starting materials was 33.65%, which was obviously enhanced by the introduction of ?-Al2O3.

Catalytic conversion of acetol over HZSM-5 catalysts – influence of Si/Al ratio and introduction of mesoporosity

Crude bio-oil from fast pyrolysis of biomass has a high oxygen content and acidity, leading to problems with corrosion and polymerization/instability. In this work, the catalytic vapor phase upgrading of acetol, a compound that is present in high concentrations in pyrolysis vapors, was investigated over three microporous HZSM-5 and four mesoporous HZSM-5 catalysts with different levels of acidity and mesoporosity. All catalysts were steam-treated prior to testing in order to attribute deactivation unambiguously to coking rather than simultaneously occurring dealumination, and catalysts were characterized by Ar and N2 physisorption, NH3-TPD, Pyridine-IR, TEM, and XRD. With increasing temperature from 400 to 500 °C the gas yield increased while the coke yield decreased, along with increased acetol conversion and increased selectivities to oxygen-free hydrocarbons in the liquid phase. Catalyst screening was conducted at 450 °C by studying the conversion of acetol as a function of increased amounts of fed reactant. CO and ethene were the major reaction products in the gas phase. At high conversions, the condensed liquid contained olefins such as iso-butene and BTX monoaromatics. With increasing amounts of acetol fed, the selectivity to oxygen-free hydrocarbons decreased while the concentration of oxygenated compounds such as ethers, ketones, and furans increased. Simultaneously, coke formation rapidly decreased the weak and strong acid sites of the zeolites. A maximum monoaromatics yield of ∼5 wt.% of fed acetol was achieved in the initial upgrading phase for the purely microporous zeolites with Si/Al = 15 and 29, while mesoporous HZSM-5 showed slightly lower yields of monoaromatics. While the coking propensity increased after introduction of mesopores, all mesoporous catalysts showed an improved capacity for converting acetol compared to their microporous versions. Mesoporous HSZM-5 prepared via desilication of parent HZSM-5 (Si/Al = 15) with a mixture of NaOH and a pore-directing agent showed the highest tolerance towards deactivation, which is attributed to a favorable combination of acid strength and the preservation of crystallinity and microporous volume with well distributed mesopores, improving the accessibility of reactants to active sites.

Enhanced bioaromatics synthesis via catalytic co-pyrolysis of cellulose and spent coffee ground over microporous HZSM-5 and HY

Catalytic co-pyrolysis (CCP) of spent coffee ground (SCG) and cellulose over HZSM-5 and HY was characterized thermogravimetrically, and a catalytic pyrolysis of two samples was conducted using a tandem micro reactor that directly connected with gas chromatography-mass spectrometry. To access the more fundamental investigations on CCP, the effects of the zeolite pore structure, reaction temperature, in-situ/ex-situ reaction mode, catalyst to feedstock ratio, and the SCG and cellulose mixing ratio were experimentally evaluated. The temperature showing the highest thermal degradation rate of cellulose with SCG slightly delayed due to the interactions during the thermolysis of two samples. HZSM-5 in reference to HY produced more aromatic hydrocarbons from CCP. With respect to the reaction temperature, the formation of aromatic hydrocarbons increased with the pyrolytic temperature. Moreover, the in-situ/ex-situ reaction mode, catalyst/feedstock, and cellulose/SCG ratio were optimized to improve the aromatic hydrocarbon yield.

Production of High-Value Chemicals by Biomass Pyrolysis with Metal Oxides and Zeolites

The catalysis of biomass pyrolysis vapors by metal oxide and zeolite was proposed to produce high-value chemicals. Metal oxides CaO and Al2O3 exhibited strong reactivity with acids and phenols with methoxyl. Acetic acid was reduced by 65.2% and 23.3% under CaO and Al2O3 catalysis, respectively, whereas guaiacols decreased by 40.4% and 27.6%, respectively. The neutralization with acids and the catalytic effect on the oxygenate groups were the main reactions of CaO, while deoxygenation on Lewis sites mainly occurred during the catalyzation by Al2O3. Since the vapors were cracked into low molecular compounds, the combination of CaO and microporous HZSM-5 showed a promotion effect on generating aromatic hydrocarbons, with 56.0% and 44.7% increases of benzene and toluene, respectively. A dual catalyst composed of CaO and mesoporous Al-MCM-41 exhibited a promotion of phenols, furans, etc., due to its large pores, which permitted more vapor to react at acid sites. The enhancement of phenols and furans was 81.2% and 8.78%, respectively. At last, the optimal temperatures for the two dual catalysts, CaO and HZSM-5 and CaO and Al-MCM-41, were 800 °C and 700 °C, respectively.

Esterification of linoleic acid using HZSM-5 zeolites with different Si/Al ratios

Abstract Microporous HZSM-5 zeolite crystals of distinct Si/Al ratios (53, 33.3 and 14.4) were compared for linoleic acid esterification with methanol as a model reaction for the production of biodiesel. As-synthesized catalytic materials were characterized using XRD, SEM, TEM, N2 sorption, X-Ray fluorescence, FTIR, and 27Al MAS NMR. The results showed that HZSM-5 with higher acidity and lower Si/Al ratio achieved high linoleic acid conversions at earlier stages of the reaction, whereas more hydrophobic zeolites reached higher conversions as reaction time increased. A maximum methyl linoleate yield of 79.78% was achieved for the esterification of linoleic acid using HZSM-5 (Si/Al = 53) at 4 h reaction time, 6:1 methanol to linoleic acid molar ratio, 10 wt% catalyst loading and 180 °C. Linoleic acid is activated by being adsorbed on the acid sites of the zeolite surface with increased Si/Al ratios and reacts to form the corresponding methyl ester.