ZSM-5 Catalysts Research Articles

Effects of transition metal doping on the properties and catalytic performance of ZSM-5 zeolite catalyst on ethanol-to-hydrocarbons conversion

In this study, the effects of transition metal-doping on the physicochemical properties and catalytic performance of HZSM-5 catalysts for the conversion of ethanol to hydrocarbons are investigated using experimental data and secondary data from the literature. Hydrothermally synthesized novel ZSM-5 catalysts were modified with different concentrations (0.5 and 10 wt%) of transition metals (Co, Fe, Ni). Characterizations, including X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, particle size distribution, N2 adsorption and NH3 temperature-programmed desorption, revealed the changes in catalyst properties. The introduction of transition metals affected the surface area, particle size and acidity without altering the MFI structures. In particular, a reduction in surface area was observed, ranging from 2.6 to 23 %, corresponding to the different metal loading of 0.5–10 wt% compared to the surface area of the pure catalyst (397.5 m²/g). In addition, metal-doping led to an increase in Lewis acid sites, accompanied by a decrease in strong acid sites. Catalytic evaluation at 350 °C and a space velocity of 12 h−1 showed improved performance in metal-doped ZSM-5 catalysts, which exhibited high selectivity towards fuel-range hydrocarbons, compared to the unmodified catalyst. Catalysts with low metal doping showed optimal catalytic activity, while high metal doping led to increased coke deposition and deactivation of the catalyst due to an increased concentration of strong acids. These results underline the suitability of metal-modified ZSM-5 for hydrocarbon reactions and provide valuable insights for the optimization of catalysts for ethanol conversion to fuel-range hydrocarbons.

Multiple synergistic roles of Zr modification on ZSM-5 in performant and stable catalyst for ethanol conversion to propene

Bioethanol to propene is a promising avenue to produce propene by non-fossil routes. In this study, the ethanol conversion on metal-modified ZSM-5 catalysts is systematically investigated under catalyst preparation conditions and reaction parameters. Among all metal modified ZSM-5, Zr modification significantly improves the propene selectivity and catalyst durability. On the Zr/ZSM-5 catalyst (Zr/Al molar ratio is 0.4, reaction temperature 500 °C, and contact time 0.005 g⋅min/mL), the maximum yield of propene reaches up to 32.5 %, which can be maintained above 20.0 % within 20 h. Zr modification changes the acidity and electronic structure of the active sites, improves the adsorption stability of the reactant ethanol on Zr/ZSM-5, facilitates easier desorption of the product propene, benefiting propene production. Moreover, Zr modification is found to increase the activation energy of the ethene protonation, inhibit the ethene dimerization reaction, further inhibits the carbon deposition, and extends the lifetime of ZSM-5. In addition to its synergistic and effective role in the conversion of ethanol to propene, the Zr modified catalyst also exhibits high selectivity and stability in the conversion of bioethanol. According to above significant characteristics, Zr modified ZSM-5 will emerge as a promising catalyst for the conversion of bioethanol to propene.

Modification of Fe on hydrophobic ZSM-5 zeolite: Optimization of adsorption and catalytic performance for decomposition of VOCs at low-temperature

The conjugation of high adsorption and excellent catalytic characteristics is desirable for the removal of volatile-organic-compounds (VOCs) at low-temperatures. In this study, ZSM-5 zeolites with varying Si/Al ratios (15, 30, 100, and 200) were synthesized using the hydrothermal-method to assess their adsorption capability for VOCs. Among them, the ZSM-5(30) sample exhibited a well-defined zeolite structure, exceptional hydrophobicity, a high surface area (SBET), and micropores, resulting in a higher toluene adsorption capacity of 135 mg/g compared to other adsorbents. Additionally, the ZSM-5(30) sample demonstrated excellent regenerative stability in both dry and humid environments. Consequently, ZSM-5(30), identified as the most effective adsorbent, was subjected to loading with various amounts of Fe metal for the catalytic-oxidation of toluene at low-temperatures. Due to its abundant oxygen-vacancies, adequate acid-sites, and various active oxygen-species, the Fe0.2/ZSM-5(30) catalyst (Fe/(Si + Al) = 0.2) not only exhibited a high adsorption capacity for toluene with good stability over five successive cycles but also demonstrated excellent performance in the catalytic oxidation of toluene. The complete conversion of toluene was attained at temperatures approximately 200 °C, with a gas hourly space velocity (GHSV) of 20,000 mL/(g∙h), and maintained stability for 40 h. Furthermore, in-situ diffuse-reflectance infrared-Fourier-transform-spectroscopy (DRIFTS) and gas chromatography-mass spectrometry (GC–MS) results, along with the Mars-Van-Krevelen model, were utilized to elucidate the adsorption and oxidation mechanism of toluene. The unique adsorption and oxidation capabilities of Fe0.2/ZSM-5(30) for toluene indicate its promising potential for the removal of VOCs in real industrial-environments. This study provides valuable insights for the design of high-performance bifunctional materials for the adsorption and catalytic-oxidation of VOCs.

Friedel-Crafts Acylation of Aromatics with Acetic Anhydrideover Nano-Sized Rare Earth Cation Exchanged ZSM-5 Catalysts

Friedel-crafts acylation of aromatic compounds used to synthesize aromatic ketones and significance has commercial importance in diverse areas of fine chemical synthesis and pharmaceutical manufacturing industry. Conventionally, acylation reactions are catalysed by corrosive metal halides or mineral acids. The present work reports on the catalytic activity of nanocrystalline ZSM-5 and rare earth metal cation such as La3+, Ce3+ and Nd3+ exchanged ZSM-5 in the liquid phase acylation of veratrole with acetic anhydride. The catalyst was thoroughly characterized for its structure. The nanocrystalline Ce-ZSM-5 displayed highest activity towards the acylation of veratrole. The catalytic performance of Ce-ZSM-5 was used to compare its activity for the acylation of other aromatics; such as toluene, anisole and veratrole. The nanocrystalline Ce-ZSM-5 shows highest activity over nanocrystalline ZSM-5 in acylation reactions of aromatics. It was established that smaller size crystal of Ce-ZSM-5showed superior activity, which is due to the enhanced density of acidic sites along with increased external surface area of smaller crystal which facilitate the activity of the acylation reaction. The catalysts used in this study are reusable without any loss of activity.

Unlocking green potential: Enhancing biomass valorization via thermal depolymerization with spent catalysts

Effective catalysts for the thermal depolymerization of biomass present an attractive way to reduce energy consumption. This study investigated the effect of spent ZSM-5 catalysts on product distribution through thermal catalytic depolymerization. The spent catalyst has similar properties to the commercial fresh catalysts, as assessed through characterization analysis. The utilization of spent catalysts can enhance the production of bio-oil. The bio-oil yields for rice straw, brown solid, alkaline, and dealkaline lignin by catalytic depolymerization are 11%, 31%, 6%, and 21%, respectively. Therefore, depolymerization using a spent catalyst is a promising method to degrade lignocellulose.

Preparation of H-[B]- ZSM -5 zeolites by hydrothermal method as a highly stable and selective catalyst for methanol to propylene (MTP) conversion

A series of high-silica boron-containing H-ZSM-5 zeolites were prepared employing the hydrothermal method. Subsequently, the physico-chemical characteristics of prepared catalysts were comprehensively studied through diverse analytical methods, followed by evaluation of catalytic performance in the methanol-to-propylene (MTP) reaction. The results demonstrated that incorporation of boron into the H-ZSM-5 zeolite induced the reduction in the total surface area and pore volume, accompanied by a raise in the density of weak acid sites. Also, the optimal point for boron content has been recognized at molar coefficient of B2O3/SiO2 = 0.025 for obtaining the highest H-[B]-ZSM-5 performance in MTP process. In comparison to unmodified H-ZSM-5, the optimized H-[B]-ZSM-5 yielded the higher selectivity towards propylene (42.9 % versus 40.1 %) and total light olefins (72.1 % versus 69.5 %), as well as propylene to ethylene ratio (8.1 versus 7.8) with a considerable reduction in selectivity toward C1–C4 alkanes (3.9 % versus 4.2 %) and heavy hydrocarbons (24.1 % versus 26.4 %). Also, the optimized H-[B]-ZSM-5 catalyst exhibited an extended lifetime of 988 h in the MTP process, surpassing the lifetime of unmodified H-ZSM-5 (936 h). These results suggest the optimal point for boron content at B2O3/SiO2 = 0.025 to attain the superior catalytic performance, specifically in terms of propylene yield and catalyst lifetime during MTP process.

Solid-state crystallization, oxygen-vacancy rich mesopores and stable triad-silanol nests in ZSM-5 catalyst induced by electron-beam irradiation and calcination

Mesopores and silanol nests are known two technological keys that essentially control the catalytic performance of ZSM-5 zeolite. However, designing and controlling them without using chemicals so that the produced ZSM-5 can have strongly enhanced catalytic properties and more importantly can be applied at industrial scale have still been a big challenge up to now. The present study employed the 10 MeV electron beam (EB) generated from an industrial linear accelerator to introduce both the O-vacancy rich mesopores and stable triad-silanol nests in ZSM-5. The structural modification of irradiated ZSM-5 samples was explored by using SEM and FTIR combined with positron annihilation spectroscopy (PAS) including positron annihilation lifetime (PAL), Doppler broadening (DB) of electron–positron annihilation energy and electron momentum distribution (EMD). Obtained results indicated that EB irradiation could recover the defective-crystal structure as well as intensively modify the structures of ZSM-5. In particular, the mechanism for the solid-state crystallization and the formation of the O-vacancy rich mesopores (maximum size of ∼4.5 nm) in ZSM-5 under the combined EB irradiation (10−110 kGy) and calcination (600 °C) was, for the first time, proposed. The mechanism for the formation of stable triad-silanol nests in the channels of irradiated and calcined ZSM-5 zeolites was also explored. The present study, therefore, opens a new research path of applying both EB irradiation and calcination to produce ZSM-5 with novel features for industrial catalytic application at large-production scale.

Mesoporous configuration effects on the physicochemical features of hierarchical ZSM-5 supported cobalt oxide as catalysts in methane partial oxidation

Hierarchical porous system has become a prevalent method to overcome the diffusion limitation of conventional zeolites. Two types of mesopores characterized as intra-crystalline (mesopores in the zeolite pore wall) and inter-crystalline mesopores (meso-sized voids between nano-zeolite aggregates) could be formed in the synthesis of hierarchical zeolites. In an attempt to investigate the influence of mesopores structure on the physicochemical properties of hierarchical ZSM-5, specifically cobalt oxide impregnated ZSM-5 zeolite samples with intra- and inter-crystalline mesopores were synthesized through two different synthesis strategies. Analysis of the physicochemical properties of the as-modified hierarchical ZSM-5 catalysts were carried out using SEM, TEM, XPS, and H2-TPR which showed distinct features given by the two mesopores configurations. Co-oxide impregnated on ZSM-5 with inter-crystalline mesopores was dominated by Co(II) species, while Co-oxide/ZSM-5 showed a fair amount of Co(III) and Co(II). Furthermore, analysis of the catalytic activity was conducted using methane partial oxidation as a model reaction. With a variation in reaction time, various types of oxygenated products, i.e. methanol, formaldehyde, formic acid, and a small trace of carbon dioxide were observed. Catalytic results suggested that the Co-oxide/ZSM-5 material with inter-crystalline mesopores configuration is more active for the methane partial oxidation reaction compared to the Co-oxide/ZSM-5 with intracrystalline mesopores. This was confirmed by the formation of formaldehyde rather than methanol as the major product in the brief reaction time of 30 min.

Catalytic stepwise pyrolysis for dechlorination and chemical recycling of PVC-containing mixed plastic wastes: Influence of temperature, heating rate, and catalyst

The viability of pyrolysis technology for chemical recycling of plastics is challenged by the presence of PVC in real-world mixed plastic wastes. This study aims to investigate catalytic stepwise pyrolysis as a pretreatment step to remove chlorine from PVC-containing plastic wastes prior to further processing. TG-FTIR and Py-GCMS analysis as well as experiments on a lab-scale pyrolysis system were conducted to study the influence of key processing parameters on the pretreatment including temperature, heating rate, and catalysts. Py-GCMS results indicated 300 °C to be the best pretreatment temperature in terms of balancing Cl removal and avoidance of organochloride formation. Metal oxides, i.e., CaO and Fe2O3, mainly acted as adsorbents of HCl gases with little cracking effect, and their adsorption effects are positively correlated with alkalinity. ZSM-5 catalysts promoted the release of HCl, and the dechlorination effect was more pronounced with ZSM-5 of higher acidity. In contrast, in the lab-scale pyrolysis system, 350 °C pretreatment achieved the highest HCl generation ratio, i.e., 43.60 %. The addition of zeolite catalyst significantly reduced the content of organochloride in the pyrolysis oil in contrast to the performance of metal oxides, but also absorbed most HCl instead of promoting HCl release as in Py-GCMS tests. Mass balance analyses revealed that the majority of chlorine was retained in the solid residues following the catalytic stepwise pyrolysis process, with the notable exception of Fe2O3. ZSM-5(25) catalyst combined with 350 °C pretreatment temperature and 550 °C final pyrolysis achieved the lowest chlorine content in the pyrolysis oil, i.e., 20 ppm, among different process conditions.

Modeling and simulation of microwave assisted catalytic pyrolysis system of waste plastics polymer for fuel production

Pyrolysis is a promising method of chemically recycling plastic waste, as it allows for the recovery of both energy and materials. In this work, a comprehensive mathematical model has been developed to predict the pyrolysis of plastic wastes over ZSM-5 catalyst in microwave-assisted pyrolysis (MAP) system for fuel production. To conduct a transient numerical analysis of the underlying processes, a lumped kinetic model that takes into account three lumped pyrolysis products (olefins, paraffins, and aromatics) is coupled with the equations that govern the microwave field, heat transfer, mass transfer, and fluid flow (Darcy's law). The distributions of electric field, temperature, and pyrolysis products within MAP are presented. The study investigated the effects of several factors on the rate of production and consumption in the pyrolysis reactions of a waste plastic mixture when using MAP. These factors include the microwave power input, the inlet velocity of the fluidizing gas, as well as the mass and particle size of the catalyst used. Increasing the input power leads to a higher intensity of the electric field, which causes a greater increase in temperature within the same time frame. The mass and particle size of the catalyst used also have a significant impact on the yield of olefins, paraffins, and aromatics. Reducing the particle size of the catalyst generally increases the reaction rate, but particle sizes smaller than 50 μm are not ideal for fluidization due to increased intermolecular forces. Increasing the inlet velocity of the fluidizing gas may result in an incomplete consumption of intermediates and a low yield of products. All in all, The MAP system is a highly efficient and effective design for using plastic waste as a source of energy, due to its superior energy efficiency and lower processing temperature compared to traditional fluidized-bed reactors.

Influence of the Mesoporosity of Hierarchical ZSM-5 in Toluene Alkylation by Methanol.

Among the different strategies to design highly shape-selective ZSM-5 to obtain para-xylene through toluene alkylation with methanol, the introduction of mesopores to increase reactant and product diffusion has been proposed but barely studied. In this study, we prepared mesoporous ZSM-5 catalysts, named ZSM5-MT(x), from commercial ZSM-5 (Si/Al = 15), using a two-step micelle-templating procedure with octadecyltrimethylammonium bromide as a surfactant in basic medium (x = NaOH/Si). These materials were used as catalysts for the alkylation of toluene by methanol at a low contact time to avoid thermodynamic equilibrium of the xylene isomers. Compared to the parent ZSM-5, the mesoporous ZSM5-MT(x) catalysts did not improve the para-xylene selectivity, revealing that the strategy of increasing diffusion in the catalyst is not a good strategy to follow. However, ZSM5-MT(0.5) showed less deactivation on stream than the parent ZSM-5. Therefore, introducing mesopores to ZSM-5 could be interesting to explore, combined with another strategy of shape selectivity, such as the passivation of the external surface acidity.

Ni and Sr modified ZSM-5 catalyst with enhanced catalytic activity for selective dehydration of bio-derived ethanol to ethylene

Ni/Sr-ZSM-5 catalyst was synthesized with tuned acidity and improved hydrothermal stability desired for the dehydration of dilute ethanol. Operating conditions were established to maximize the ethylene selectivity from ethanol dehydration by controlling side reactions, using 6% aqueous ethanol as a model feedstock for fermenter broth. Detailed characterization data of the catalyst reveals that Ni in the catalyst is responsible for the enhanced, near quantitative ethylene selectivity at optimum reaction conditions (temperature of 250 °C, 9 h−1 WHSV), the Ni/Sr-ZSM-5 catalyst exhibited >96% conversion of ethanol with 95% yield of ethylene, facilitated by discouraging undesired side reactions of ethanol. The role of Sr is observed to improve the hydrothermal stability of the catalyst, allowing it to function even in the presence of 94% water in the feed at operated reaction conditions, as evidenced by its stable operation in the studied period of 30 h without significant loss in catalytic activity. The rate of ethylene formation with Ni/Sr-ZSM-5 was 5.33×10 −3 molgcat−1s−1, which is higher than neat H-ZSM-5. This study highlights the production of ethylene from low concentration feedstock using a catalyst with enhanced catalytic activity even in the presence of water in the feedstock.

Aromatics production from relay catalytic pyrolysis of cow manure using Ru/C and ZSM-5 dual catalysts synthesized from coal gasification fine slag

Resource utilization of solid waste can aid in gradual substitution of fossil fuels while achieving waste recycling. In this study, residual carbon and ash slag from the coal gasification fine slag were separated by froth flotation, and then was used to prepare Ru/C and ZSM-5 dual catalysts with carbon-rich and ash-rich components as raw materials, respectively. The performance of two catalysts for catalytic upgrading of volatiles from pyrolysis of cow manure (CM) to produce light aromatic hydrocarbons was systematically investigated. The direct pyrolysis products of CM mainly included alcohols, ketones, ethers, and other oxygen-containing compounds. When ZSM-5 was used as the catalyst, the yield of monocyclic aromatic hydrocarbons (MAHs) increased significantly due to the better catalytic cracking and aromatization abilities of ZSM-5 catalyst. However, the yield of phenols in the pyrolysis products improved when Ru/C was used as the catalyst due to the cleavage effect of Ru/C on the C–O bond. When Ru/C and ZSM-5 were used as dual catalysts in relay catalytic pyrolysis of volatiles, the increase in MAHs yield in the pyrolysis product was higher than the total increase obtained under Ru/C and ZSM-5 single catalysis. The possible pathways for the generation of MAHs from CM under Ru/C and ZSM-5 relay catalytic pyrolysis were revealed by the pyrolysis experiment performed on model compounds.

Research Progress of the Selective Catalytic Reduction with NH3 over ZSM-5 Zeolite Catalysts for NOx Removal

Nitrogen oxides (NOx) are very common air pollutants that are harmful to the environment and human bodies. Selective catalytic reduction with ammonia (NH3-SCR) is considered an effective means to remove NOx emissions due to its good environmental adaptability, high catalytic activity, and remarkable selectivity. In this paper, the preparation methods, types, advantages, and challenges of ZSM-5 catalysts are reviewed. Special attention is paid to the catalytic properties and influence factors of ZSM-5 catalysts for NH3-SCR. The SCR performances of ZSM-5 catalysts doped with single or multiple metal ions are also reviewed. In addition, the environmental adaptabilities (sulfur resistance, alkali resistance, water resistance, and hydrothermal stability) of ZSM-5 catalysts are discussed, and the development of ZSM-5 catalysts in denitrification is summarized.

Ca/ZSM-5 catalysts for the methanol-to-hydrocarbons reaction: Activity – Selectivity trade-off?

Establishing structure–activity relationships for the methanol-to-hydrocarbons reaction can help to identify better catalysts and optimal reaction conditions. Modification of ZSM-5 catalysts with alkaline-earth cations such as Ca increases the selectivity to C3+ olefins, which has been linked to a change in the effective pore geometry, affecting the formation of particular hydrocarbon pool (HCP) components. To further understand the catalytic properties of Ca/ZSM-5, we estimated the methanol conversion rate constants and deactivation coefficients. The kinetic experiments were carried out at different contact times with and without water in the feed. Ca/ZSM-5 is substantially less active than HZSM-5 and Na/ZSM-5 in a wide range of conditions. The decreased activity can be correlated to a different composition of the HCP due to the presence of Ca, which is supported by step-response IR experiments using various feed mixtures (methanol, methanol + water, water). Ca/ZSM-5 converts methanol significantly slower than HZSM-5 and Na/ZSM-5 but with a higher C3+ olefins selectivity, pointing to the delicate balance between activity and selectivity in these materials.

On the transition to gasoline-to-olefins chemistry in the cracking reactions of 1-octene over H-ZSM-5 catalysts

The cracking reactions of 1-octene over H-ZSM-5 zeolite are studied via micro-reactor and off-line spectroscopic techniques for up to 72 h on stream and a temperature range of 473–673 K. 1-Octene is found to react via a two-cycle hydrocarbon pool mechanism, with strong similarities to that reported for methanol-to-hydrocarbons chemistry. This dual-cycle mechanism requires temperatures of 673 K or higher to function with full efficiency, with lower temperatures deactivating portions of the cyclic mechanism, leading to premature deactivation of the catalyst through over-production of coke species. Inelastic neutron scattering is used to study the coke composition, identifying two distinct deactivation mechanisms depending on reaction temperature. The catalyst is also found to slowly progress from an aromatic-heavy to an olefin-heavy product regime even at full efficiency due to progressive blockage of active sites by amorphous carbon-rich coke. Artificial aging of the zeolite, through steam treatment, is found to shift the catalyst lifetime so that it commences at a later stage in this process, resulting in increased light olefin production. The reduced aromatic production also means that deactivation of the catalyst occurs more slowly in steamed catalysts than in fresh ones, after an equivalent time-on-stream. Collectively, these observations connect with the application of ZSM-5 catalysts to facilitate gasoline-to-olefins chemistry in fluidised catalytic cracking unit operations.

Metallised seaweed-derived bio-char catalyst preparation and its application in the pyrolysis process for the waste fishing nets and marine biomass utilisation

Marine biomass and plastic wastes are one of the most significant ecological issues of water pools, which could be adapted for energy recovery through pyrolysis. Moreover, a catalytical process could be applied to improve the quality and adaptability of the formed product. This study investigates seaweed (SWD) and fishing nets (FN) standalone pyrolysis with and without commercial ZSM-5 catalysts. Therefore, the newly created seaweed char-based metals (iron and copper) impregnated catalysts were investigated using SEM-EDS, XRD, and pore size distribution examination and applied for the selected feedstock pyrolysis process. The study revealed that bio-char contains 335 m2/g of surface area, while the impregnation process increased it to 1066 and 790 m2/g with copper and iron, respectively. Pyrolysis products investigation showed that the main derivatives of the FN liquid fraction are caprolactam and hexanenitrile, while the SWD liquids mainly consist of variously substituted aromatic and phenolic compounds. Copper-impregnated catalyst increased the amount of caprolactam to 54.3 % and hexanenitrile to 31.7 % (FN), while the amount of toluene was increased to 84.2 % (SWD) in the total liquid fraction. This research provides information regarding the promising route of newly created biochar preparation and application as a catalyst for the pyrolysis product upgrading.

Unconventional seed-assisted strategy for Al-rich hierarchical ZSM-48 zeolite

Inferior diffusion capacity and insufficient acid density hinder the practical application of ZSM-48 zeolite. Finding a simple and practical strategy to simultaneously address these two defects remains a challenge. In response to this dilemma, we developed an unconventional seed-assisted synthesis strategy for Al-rich hierarchical ZSM-48 zeolite. This approach allows for achieving a broader range of silica to alumina ratio and accelerates the entire crystallization process through the selection of unconventional seeds. The synergy between the seed and organic template was demonstrated to play a pivotal role in facilitating nucleation. Direct evidence from 1H-29Si CP MAS NMR, TG, and IR results demonstrates that hexamethonium ions (HM2+) electrostatically adsorb at the defect sites on the seed, thereby promoting nucleation sites formation. Smaller seed crystals undergo more etching during the induction period, resulting in additional defects and enhanced nucleation ability. The obtained catalyst exhibits a diffusion time constant (Deff/L2) nine times that of conventional ZSM-48 zeolite when using p-xylene as a probe molecule. In m-xylene isomerization reaction, Al-rich hierarchical ZSM-48 demonstrates excellent stability along with higher selectivity and yield for p-xylene compared to typical ZSM-5 catalysts. Remarkably, long-term testing of 1000 h yields over 22.5 % of p-xylene, indicating the potential of this catalyst as an alternative for xylene isomerization reaction. This work not only advances the practical application process of ZSM-48 catalyst but also provides valuable insights for optimizing other zeolites.

Optimizing zeolitic hierarchical pore structure to boost the direct conversion of aromatics from syngas over the iron-based/zeolite bifunctional catalysts

The utilization of iron-based/ZSM-5 bifunctional catalysts for converting syngas to aromatics (STA) has garnered significant interest because of its cost-effectiveness. This study aims to elucidate the regulatory mechanism of zeolitic pore structure on the performance of the bifunctional catalyst in STA reaction. The relationship among the mesoporosity and mesoporous diameter of hierarchical ZSM-5 zeolite component, product distribution, and catalyst stability is investigated through a range of analyses techniques, including XRD, SEM, TG, Raman, N2-adsorption and desorption. The results demonstrate that as the mesoporosity of zeolite increased to 78.9%, the lifetime of the iron-based/ZSM-5 bifunctional catalyst extended beyond 96 h and maintained the aromatics selectivity over 40% at 2 MPa, 320 °C, and 3000 h−1. This outcome can be attributed to the role of high mesoporosity in restraining coke formation in zeolites. Moreover, the reduction in mesopore size from 11.1 to 5.8 nm results in an increased aromatics selectivity from 39.6% to 43.4%, and the fraction of light aromatics rose from 48.8% to 54.5%, indicating that small mesopore size can also expedite the production of aromatics, particularly light aromatics. It is thus concluded that the improvement of aromatics selectivity and stability of iron-based/ZSM-5 bifunctional catalysts in STA reaction can be achieved by increasing the mesoporosity and decreasing the mesopore size of the zeolite component.

Biomass pyrolysis in a circulating fluidized bed reactor: Evaluating two strategies for the reduction of oxygen content in bio-oil

The use of a circulating fluidised bed (CFB) reactor promotes higher heat transfer to the biomass pyrolysis process and has the advantage of being energy self-sufficient through the continuous burning of biochar. CFB’s similarity with the fluidised catalytic cracking (FCC) of fossil streams represents a promising scenario of integration of lignocellulosic biomass in a conventional refining scheme. In this paper, two approaches were studied to enhance the deoxygenation reactions of biomass components in a pilot pyrolysis CFB reactor. First, in a noncatalytic pyrolysis, a lignocellulosic biomass was cofed with hydrogen-rich compounds produced in the oil refinery (methane and propane). In the second part, using a ZSM-5 catalyst in the bed, the effect of different catalyst-to-biomass ratios (CTB) in the bio-oils’ properties was evaluated. Compared with conventional pyrolysis, the cofeeding of methane or propane produced bio-oils with less oxygen content. The use of propane achieved better performance in terms of hydrocarbon concentrations in bio-oils, hence increasing benzene, toluene and xylene (BTX) production and being comparable with the results of catalytic pyrolysis. It was also shown that the increase of CTB in catalytic pyrolysis led to the enhancement of deoxygenation reactions, producing more O-free compounds. Both strategies were promising for improving the quality of bio-oil. Issues such as the cost of the catalyst and gases must be evaluated for possible integration into a conventional refining process.