Aromatic Selectivity Research Articles

Production of aromatic hydrocarbons from catalytic fast pyrolysis of microalgae over Fe-modified HZSM-5 catalysts.

In this study, catalytic fast pyrolysis of the microalga C. pyrenoidosa over Fe-modified HZSM-5 catalysts was performed to produce aromatic hydrocarbons using analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Fe-modified HZSM-5 catalysts were prepared using wet impregnation and characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption and temperature-programmed desorption of ammonia (NH3-TPD) analysis. The effect of Fe loading (3, 5, 8, and 12 wt%) and pyrolysis temperature (450, 500, 550, 600 °C) on the content of pyrolysis products and the content and selectivity of aromatics was examined. Results showed that the parent HZSM-5 catalyst structure remained intact upon increasing Fe loading, although its specific surface area, micropore volume and average pore diameter decreased. In addition, its external specific surface area and total pore volume increased. The modification of Fe metal increased the total acid amount, especially strong acid sites, which were highest when Fe loading was 8 wt%. The prepared Fe-modified HZSM-5 catalysts exhibited pronounced deoxygenation and denitrogenation effects, which significantly decreased the acid, aldehyde, ketone, furan and nitrogenous compounds, thus improving the production of monocyclic aromatic hydrocarbons (MAHs) while effectively suppressing the formation of polycyclic aromatic hydrocarbons (PAHs). The highest content of aromatic hydrocarbons was obtained with an Fe loading of 8 wt% and pyrolysis temperature of 500 °C, which was 42.5%. As Fe loading increased, benzene selectivity decreased, while the selectivity of toluene and xylene first increased and then decreased. With an increase in pyrolysis temperature, benzene selectivity increased, whereas toluene and xylene selectivity increased at first and then decreased. Reaction mechanisms for the formation of aromatic hydrocarbons during the catalytic pyrolysis of microalgae are put forward. This research revealed that catalytic fast pyrolysis of microalgae over Fe-modified HZSM-5 catalysts is an effective method to produce MAHs.

Insight into the coke alleviation pattern over iron-based and boron-modified HZSM-5 bifunctional catalyst for direct CO2 hydrogenation to aromatics

Carbon dioxide (CO2) hydrogenation to aromatics is promising for reducing the burden of petroleum fuels. Herein, iron-based catalyst was mixed with boron modified HZSM-5 with pre-treatment and post-treatment method. The textural, acidic and element distribution properties over zeolite framework and external surface were studied. Combining with characterizations for internal and external coke, the element distribution-acidity-coke-stability relationship over boron-modified zeolite was put forward. Pre-treated zeolite witnessed reduced amount of external and total Brönsted acid sites (BAS) with similar degree, and increase paired Al (Alpair) fraction in the intersection site, leading to increased aromatics selectivity and reduced coke amount. While boron post-treatment significantly reduced external surface BAS and inhibited formation of condensed external coke. Afterwards, the mechanism of olefins aromatization was studied and found that PT-Z5-B greatly suppressed the overalkylation of light aromatics, thus alleviating the co-deactivation pattern generated by transformation of coke precursors from zeolite to iron-based catalyst.

Research on Deoxygenation Pyrolysis of Larch Based on Microwave Heating

Aiming at problems such as low energy utilization efficiency and the high oxygen content of liquid products in the process of conventional biomass conversion to prepare liquid fuels, the deoxygenation pyrolysis technology route of larch based on microwave heating was proposed in this paper. Two kinds of calcium–iron composite oxygen carriers, including Ca2Fe2O5 with iron ore structure and CaFe2O4 with spinel structure, were successfully synthesized. The results showed that the selectivity of ideal products was improved under the action of single iron-based oxygen carriers; however, the deoxygenation effect was undesirable. Under the action of CaFe2O4, the selectivity of aromatics was increased to 27.17% and the selectivity of phenols was decreased to 36.46%, which mainly existed in the form of O1P with low oxygen content. The oxygen content of bio-oil was reduced to 27.70% and the calorific value was increased to 29.05 MJ/kg, thus leading to a great improvement in the quality of liquid products. After the pyrolysis reaction, the Fe2P3/2 XPS peak of CaFe2O4 shifted to a higher binding energy and was characterized as higher valence of iron oxide, which proved its “oxygen grabbing” capacity in microwave pyrolysis. The deoxygenation conversion of larch without an external hydrogen supply was achieved.

Ni/ZSM-5@Ni/ZnO catalysts for fluid catalytic cracking gasoline desulfurization-aromatization tandem reactions

The production of cleaner gasoline requires reducing sulfur and olefin content in fluid catalytic cracking (FCC) gasoline. Herein, Ni/ZSM-5@Ni/ZnO catalysts were synthesized by uniformly coating Ni/ZnO on the surface of Ni/ZSM-5 by electrostatic induced crystallization strategy for FCC gasoline desulfurization-aromatization tandem reactions. The desulfurization activity of Ni/ZSM-5@Ni/ZnO has superior desulfurization activity due to the smaller size of ZnO, higher O vacancy content, and more uniform dispersion of Ni and ZnO relative to the physically mixed Ni/ZSM-5-Ni/ZnO. In addition, coating Ni/ZnO on the surface of Ni/ZSM-5 can reduce the Brønsted acid content of Ni/ZSM-5, increase the Lewis/Brønsted acid value of the catalyst, which inhibits the excessive cracking of FCC gasoline, and improves the liquid yield and aromatics selectivity. After 8 h of reaction, the desulfurization rate, aromatics generation rate and olefin conversion rate of Ni/ZSM-5@Ni/ZnO were 85.58 %, 25.22 % and 49.08 % respectively, which were higher than those of physically mixed Ni/ZSM-5-Ni/ZnO catalysts by 25.34 %, 15.95, and 12.98 %, respectively. Meanwhile, the unique structure of Ni/ZSM-5@Ni/ZnO reduces carbon deposition and delays catalyst deactivation. Density functional theory calculations show that Ni/ZSM-5@Ni/ZnO was more favorable for thiophene desulfurization and has a better ability to adsorb and activate H2. This study provides a new idea for the development of catalysts for clean gasoline production.

Combination of Hollow Capsule Structure and Zn Uniform Load for the Conversion of Methanol to Aromatics over Zn/ZSM-5 Zeolites.

As an important nonoil route for acquiring aromatics, the highly efficient conversion of methanol to aromatics over Zn/ZSM-5 zeolites remains an ongoing challenge. In this work, we developed a uniform loading approach of zinc and further combined it with a hollow capsule structure to design the high-performance Zn/ZSM-5 catalyst. The electrostatic assembly among EDTA3-, n-butylamine+ and negative silica-alumina gel gave rise to an "Inorganic-Organic Hybrid Sphere" in form of Na(l+m+n+3x)-(y+z)·{[(SiO)4Al-]l/(SiO-)m(n-butylamine+)y(EDTA3-)x(n-butylamine+)z(SiO-)n, which further transformed into mesoporous aluminosilicates sphere (MASS) through calcination. The characteristic of abundant mesopore guaranteed MASS fantastic ability to evenly incorporate Zn ingredient inside, and the resultant Zn/MASS further served as a "hard template" for the direct synthesis of Hollow Zn/ZSM-5 capsules, rather than after impregnation. When tested in the methanol-to-aromatics (MTA) process, the direct synthesis method not only facilitated the homogeneous dispersion of the Zn ingredient, but also benefited for the generation of more (ZnOH)+ sites and strengthened their synergism with zeolite acid for the superior aromatics selectivity (50.63%). Meanwhile, the hollow capsule structure increased the contact time of MTA intermediate products with the Zn/ZSM-5 shell, and it increased the coke-admitting capacity and suppressed the coke rate, which maintained quite an excellent stability (131 h). Therefore, the above combination of hollow capsule structure and uniform load of Zn ingredient brings forward a wide prospect to develop zeolite materials with excellent properties in catalysis.

Non‐Oxidative Dehydroaromatization of Linear Alkanes on Intermetallic Nanoparticles

AbstractThere has been significant interest in developing new catalytic systems to convert linear chain alkanes into olefins and aromatics. In the case of higher alkanes (≥C6), the production of aromatic compounds such as benzene‐toluene‐xylenes is highly desirable. However, as the length of the carbon chain increases, the dehydrogenation process becomes more complex, not only due to the challenges of C−H activation but also the need for selectivity towards the desired products by the possibility of side reactions such as isomerization and cracking. Here, we present a detailed analysis of the dehydroaromatization of n‐hexane, n‐heptane, and n‐octane, using PtSn intermetallic nanoparticles supported on SBA‐15 as the catalyst. Through in situ spectroscopic and kinetic analysis, we have probed the reaction kinetics and catalyst deactivation, and provided a mechanistic understanding of the dehydroaromatization process on the surface of the PtSn intermetallic nanoparticles. Introducing Sn has been shown to be crucial not only for enhancement of catalytic activity, but also for higher aromatics selectivity and stability on stream. Furthermore, the analysis of dehydroaromatization reaction rates of reactant and possible intermediates indicates that the dehydroaromatization of n‐hexane to benzene likely proceeds through initial dehydrogenation steps followed by ring closing.

The Paradoxical Influence of Hydrothermally Treated Zeolites on the Hydrocarbon Pool Mechanism.

Understanding the mechanistic intricacies of hydrothermally treated zeolite is crucial for valorizing any oxygen-containing renewable feedstocks (e.g., methanol, carbon dioxide, biomass). Additionally, the regeneration of deactivated zeolite catalysts under oxidative conditions, akin to hydrothermal treatment, is essential in industrial processes. While research in this area has predominantly focused on characterizing steaming-induced physicochemical changes in zeolite, their ultimate impact on the organic reaction mechanism governed by the hydrocarbon pool dual-cycle mechanism remains unclear. To bridge this knowledge gap, this study investigates the effect of steamed zeolite on the organic reaction mechanism during the industrially significant methanol-to-hydrocarbons process. We achieved this objective by strategically integrating catalytic and control experiments over the pristine and steamed zeolites and their advanced characterization, including under operando conditions, XRD structural refinement, and using "mobility-dependent" solid-state NMR spectroscopy. This multimodal characterization approach was instrumental in elucidating elusive mechanistic information in the dual-cycle mechanism, shedding light on phenomena such as the unchanged ethylene selectivity despite decreasing aromatics selectivity, while ethylene could solely be derived from arene-based reaction intermediates. This study could improve the process efficiency in zeolite catalysis by connecting steaming-induced changes in the organic reaction mechanisms with inorganic material aspects.

The Paradoxical Influence of Hydrothermally Treated Zeolites on the Hydrocarbon Pool Mechanism

Understanding the mechanistic intricacies of hydrothermally treated zeolite is crucial for valorizing any oxygen‐containing renewable feedstocks (e.g., methanol, carbon dioxide, biomass). Additionally, the regeneration of deactivated zeolite catalysts under oxidative conditions, akin to hydrothermal treatment, is essential in industrial processes. While research in this area has predominantly focused on characterizing steaming‐induced physicochemical changes in zeolite, their ultimate impact on the organic reaction mechanism governed by the hydrocarbon pool dual‐cycle mechanism remains unclear. To bridge this knowledge gap, this study investigates the effect of steamed zeolite on the organic reaction mechanism during the industrially significant methanol‐to‐hydrocarbons process. We achieved this objective by strategically integrating catalytic and control experiments over the pristine and steamed zeolites and their advanced characterization, including under operando conditions, XRD structural refinement, and using “mobility‐dependent” solid‐state NMR spectroscopy. This multimodal characterization approach was instrumental in elucidating elusive mechanistic information in the dual‐cycle mechanism, shedding light on phenomena such as the unchanged ethylene selectivity despite decreasing aromatics selectivity, while ethylene could solely be derived from arene‐based reaction intermediates. This study could improve the process efficiency in zeolite catalysis by connecting steaming‐induced changes in the organic reaction mechanisms with inorganic material aspects.

Selectivity Descriptors of Methanol-to-Aromatics Process over 3-Dimensional Zeolites.

The zeolite-catalyzed methanol-to-aromatics (MTA) process is a promising avenue for industrial decarbonization. This process predominantly utilizes 3-dimensional 10-member ring (10-MR) zeolites like ZSM-5 and ZSM-11, chosen for their confinement effect essential for aromatization. Current research mainly focuses on enhancing selectivity and mitigating catalyst deactivation by modulating zeolites' physicochemical properties. Despite the potential, the MTA technology is at a low Technology Readiness Level, hindered by mechanistic complexities in achieving the desired selectivity towards liquid aromatics. To bridge this knowledge gap, this study proposes a roadmap for MTA catalysis by strategically combining controlled catalytic experiments with advanced characterization methods (including operando conditions and "mobility-dependent" solid-state NMR spectroscopy). It identifies the descriptor-role of Koch-carbonylated intermediates, longer-chain hydrocarbons, and the zeolites' intersectional cavities in yielding preferential liquid aromatics selectivity. Understanding these selectivity descriptors and architectural impacts is vital, potentially advancing other zeolite-catalyzed emerging technologies.

Reactivity and stability of Ni encapsulated hierarchical HZSM-5 for lignite-to-aromatics via catalytic pyrolysis

Metal-zeolite composite catalysts, as a special type via metallic encapsulation technology, hold great promise for lignite-to-aromatics conversion due to their high activity, shape-selectivity, and stability. However, the key issues lie in the location of the efficient metal sites and the nature of coke evolved in metal-encapsulated zeolites. Herein, we reported an efficient in situ encapsulation method to confine Ni species inside hierarchical channels and on the surface of HZSM-5 (i.e., Ni-HeZ5) assisted by water-soluble carbon black as hard template. Compared to core-shell Ni-impregnated hierarchical HZSM-5 (i.e., Ni@HeZ5), Ni-HeZ5 exhibited high activity, good stability and enhanced coke resistance in lignite-to-aromatics conversion via catalytic pyrolysis under an H2 atmosphere. The selectivity for light aromatics reached 93.6% in a single-pass reaction. The Ni species on the surface and within the zeolite were evidenced to facilitate, respectively, the cracking reaction of aliphatics and light oxygenates to produce olefins, and the secondary reaction of olefines to produce aromatics. The coke deposition and its influence on deactivation of Ni-HeZ5 and Ni@HeZ5 were studies based on coke location, chemical nature and formation mechanism. The principle of coke development in lignite-to-aromatics conversion is different from that in biomass-to-aromatics conversion. The heavy aliphatic coke deposits, which undergo chain-growth, play a more significant role in catalyst deactivation than the aromatic coke species. This work provides a facile strategy for designing metal-encapsulated zeolites (i.e., balancing the internal and external metallic sites on hierarchical channels) for lignite-to-aromatics conversion.

Stepwise dechlorination and co-pyrolysis of poplar wood with dechlorinated polyvinyl chloride: Synergistic effect and products distribution

With the combination of stepwise dechlorination and co-pyrolysis techniques, this study conducted polyvinyl chloride (PVC) dechlorination experiments and co-pyrolysis experiments of poplar wood (PW) with dechlorinated polyvinyl chloride (DPVC) by thermogravimetric analysis and a fixed bed reactor. Stepwise pyrolysis effectively removed Cl from PVC with a dechlorination efficiency of 99.84 % at 360 °C for 30 min. Thermogravimetric tests and thermokinetic variables were employed to describe the co-pyrolysis process's thermodynamic behavior, where co-pyrolysis significantly diminished the activation energy of the initial pyrolysis stage (9.65–21.62 kJ/mol) and increased the reaction rate (0.02–0.09 %/°C). The synergistic effect of co-pyrolysis enhanced the yield and quality of liquid oil and reduced the solid residue rate, with the maximum change in solid residue rate (−2.36 wt%) occurring at PW:DPVC = 3:7. The optimal conditions for the synergistic effect are a raw material ratio of 3:7 at 500 °C. Co-pyrolysis efficiently reduced the content of oxygen-containing compounds of phenols, ketones, and acids in oil, and elevated the selectivity of aromatics. The research methods avoid the drawbacks of bio-oil and plastic oil and improve the quality of pyrolysis oil in a concise and efficient manner, which provides some new ideas for the resource and clean utilization of municipal waste.

Catalytic hydrogenation of CO2 to aromatics over indium-zirconium solid solution and sheet HZSM-5 tandem catalysts

The presence of acids and bases, coupled with its exceptional CO2 adsorption capacity and thermal stability, has established zirconia as a highly esteemed promoter and carrier. Researchers have found that the In2O3 supported ZrO2 exhibits high activity and remarkable stability. Therefore, xIn-yZr(T) solid solutions were prepared with different calcination temperatures and In/Zr molar ratios. The solid solutions were then combined with sheet HZSM-5 zeolite from tandem catalysts, which were investigated for their catalytic performance in converting CO2 to aromatics. The X-ray diffraction, scanning electron microscopy, N2 adsorption-desorption, NH3 temperature-programmed desorption, pyridine infrared radiation, X-ray photoelectron spectroscopy, electron paramagnetic resonance, CO2 temperature-programmed desorption and H2 temperature-programmed reduction characterization methods were used to investigate the physicochemical properties of catalysts. Density Functional Theory calculations were used to investigate the energy of thermal desorption and H2 reduction to generate oxygen vacancies on the surface of In2O3(111) and Zr/In2O3(111). Additionally, the influence of oxygen vacancies on CO2 adsorption energies was simulated. It was found that the incorporation of a moderate amount of zirconium carriers promoted the generation of oxygen vacancies and provided better metal-carrier interactions. The 4In-1Zr(500 °C)/HZSM-5 tandem catalyst exhibits excellent catalytic stability, achieving a CO2 conversion of 24.3 % and aromatics selectivity of 37.3 %.

Hydrogenation of CO2 to p-xylene over ZnZrOx/hollow tubular HZSM-5 tandem catalyst

The conversion of CO2 into specific aromatics by modulating the morphology of zeolites is a promising strategy. HZSM-5 zeolite with hollow tubular morphology is reported. The morphology of zeolite was precisely controlled, and the acid sites on its outer surface were passivated by steam-assisted crystallization method, so that the zeolite exhibits higher aromatic selectivity than sheet HZSM-5 zeolite and greater p-xylene selectivity than chain HZSM-5 zeolite. The tandem catalyst was formed by combining hollow tubular HZSM-5 zeolites with ZnZrOx metal oxides. The para-selectivity of p-xylene reached 76.2% at reaction temperature of 320 °C, pressure of 3.0 MPa, and a flow rate of 2400 mL g−1 h−1 with an H2/CO2 molar ratio of 3/1. Further research indicates that the high selectivity of p-xylene is due to the pore structure of hollow tubular HZSM-5 zeolite, which is conducive to the formation of p-xylene. Moreover, the passivation of the acid site located on the outer surface of zeolite effectively prevents the isomerization of p-xylene. The reaction mechanism of CO2 hydrogenation over the tandem catalyst was investigated using in-situ diffuse reflectance Fourier transform infrared spectroscopy and density functional theory. The results showed that the CO2 to p-xylene followed a methanol-mediated route over ZnZrOx/hollow tubular HZSM-5 tandem catalysts. In addition, the catalyst showed no significant deactivation in the 100 h stability test. This present study provides an effective strategy for the design of catalysts aimed at selectively preparing aromatics through CO2 hydrogenation.

Selectivity Descriptors of Methanol‐to‐Aromatics Process over 3‐Dimensional Zeolites

AbstractThe zeolite‐catalyzed methanol‐to‐aromatics (MTA) process is a promising avenue for industrial decarbonization. This process predominantly utilizes 3‐dimensional 10‐member ring (10‐MR) zeolites like ZSM‐5 and ZSM‐11, chosen for their confinement effect essential for aromatization. Current research mainly focuses on enhancing selectivity and mitigating catalyst deactivation by modulating zeolites′ physicochemical properties. Despite the potential, the MTA technology is at a low Technology Readiness Level, hindered by mechanistic complexities in achieving the desired selectivity towards liquid aromatics. To bridge this knowledge gap, this study proposes a roadmap for MTA catalysis by strategically combining controlled catalytic experiments with advanced characterization methods (including operando conditions and “mobility‐dependent” solid‐state NMR spectroscopy). It identifies the descriptor‐role of Koch‐carbonylated intermediates, longer‐chain hydrocarbons, and the zeolites′ intersectional cavities in yielding preferential liquid aromatics selectivity. Understanding these selectivity descriptors and architectural impacts is vital, potentially advancing other zeolite‐catalyzed emerging technologies.

Reducing Solvent Consumption in Reductive Catalytic Fractionation through Lignin Oil Recycling.

Reductive catalytic fractionation (RCF) enables the simultaneous valorization of lignin and carbohydrates in lignocellulosic biomass through solvent-based lignin extraction, followed by depolymerization and catalytic stabilization of the extracted lignin. Process modeling has shown that the use of exogenous organic solvent in RCF is a challenge for economic and environmental feasibility, and previous works proposed that lignin oil, a mixture of lignin-derived monomers and oligomers produced by RCF, can be used as a cosolvent in RCF. Here, we further explore the potential of RCF solvent recycling with lignin oil, extending the feasible lignin oil concentration in the solvent to 100 wt %, relative to the previously demonstrated 0-19 wt % range. Solvents containing up to 80 wt % lignin oil exhibited 83-93% delignification, comparable to 83% delignification with a methanol-water mixture, and notably, using lignin oil solely as a solvent achieved 67% delignification in the absence of water. In additional experiments, applying the RCF solvent recycling approach to ten consecutive RCF reactions resulted in a final lignin oil concentration of 11 wt %, without detrimental impacts on lignin extraction, lignin oil molar mass distribution, aromatic monomer selectivity, and cellulose retention. Overall, this work further demonstrates the potential for using lignin oil as an effective cosolvent in RCF, which can reduce the burden on downstream solvent recovery.

Hierarchical HZSM-5 catalysts enhancing monocyclic aromatics selectivity in co-pyrolysis of wheat straw and polyethylene mixture

The limitation in bio-oil quality hampers its further utilization in the fuel or chemical industry. This study employed a combination of tetra propylammonium hydroxide (TPAOH) and NaOH solutions for HZSM-5 desilication to enhance the yield of monocyclic aromatic hydrocarbons in the catalytic co-pyrolysis of wheat straw with polyethylene. Results revealed hierarchical HZSM-5, prepared with equal mole concentrations of NaOH and TPAOH, exhibited optimal catalytic performance. The bio-oil from this process had an aromatic content of 72 %, with monocyclic aromatic hydrocarbons (MAHs) constituting 56.26 %. Further optimization was achieved through iron modification of hierarchical HZSM-5. The addition of 0.5 % iron-modified hierarchical HZSM-5 increased the aromatic hydrocarbons to 80.57 %, with BTX compounds (benzene, toluene, and xylene) reaching a selectivity of 61.9 %. This approach reduced polycyclic aromatic hydrocarbons (PAHs), contributing to less coke formation, presenting a promising method for high-quality bio-oil.

The series of L-lysine-derived gelators-modified multifunctional chromatography stationary phase for separation of chiral and achiral compounds

In this study, using chiral L-lysine as the molecular skeleton, three kinds of L-lysine-derived gelators (GBLB, GBLF and GFLF) were synthesized and then bonded to the surface of silica matrix (5 μm) by amide condensation to prepare a series of multifunctional chromatography stationary phases (GBLB-SiO2, GBLF-SiO2, and GFLF-SiO2) were prepared. The L-lysine-derived gelators not only possess chiral recognition ability, but also can spontaneously form oriented and ordered network structures in liquid medium through the interaction of non-covalent bonding forces such as hydrogen bonding, π-π stacking, and van der Waals forces. The comprehensive effect of multiple weak interaction sites enhances the molecular recognition ability and further improves the separation diversity of different types of compounds on stationary phases. The separation and evaluation of chiral compounds showed that benzoin, 1-phenyl-ethanol, 1-phenyl-propanol and 6-hydroxyflavanone could be separated in normal phase mode (NPLC). The separation of different types of non-chiral compounds, such as sulfonamides, nucleosides, nucleobases, polycyclic aromatic hydrocarbons (PAHs), anilines, and aromatic acids, were achieved in hydrophilic interaction/reversed-phase/ion-exchange mode (HILIC/RPLC/IEC), and the separation of polarized compounds could be performed under the condition of ultrapure water as the mobile phase, which has the typical retention characteristics of per aqueous liquid chromatography (PALC). The effects of organic solvent content, temperature, pH value, and buffer salt concentration on the retention and separation performance of the column were investigated. Comparison of the three prepared columns showed that the separation performance (such as aromatic selectivity) could be improved by increasing the types of functional groups on the surface of the stationary phase and the number of aromatic groups. In a word, the prepared stationary phase have multiple retention properties, can simultaneously separate chiral compounds and various types of achiral compounds. This work provides an idea for developing multifunctional liquid chromatography stationary phase materials, and further expands the application of gelators in separation science.

The effect of hydrothermal pretreatment on the catalytic performance of Zn/HZSM-5 catalysts for ethylene aromatization reaction

To address the issue of coking and deactivation of Zn/HZSM-5 catalysts used for lightolefins aromatization, a high-temperature hydrothermalmethod was employed for catalyst pretreatment. The catalysts were characterized using XRD, N2 physical adsorption-desorption, NH3-TPD, Py-FTIR, XPS, and TG techniques. The effect of high-temperaturehydrothermal pretreatment on the catalytic performance and stability of the catalyst was investigated using ethylene aromatization as a probe reaction. The results showed that the Zn/HZSM-5 catalyst exhibited excellent catalytic performance after48 h of high-temperature hydrothermal pretreatment. Although the conversion of ethylene slightly decreased, the catalyst lifetime was significantly extended, increasing from 72to 216 h, while the aromatics selectivity remained above 60%. It was suggested that the hydrothermal treatment enhanced the interaction between ZnO species and Brønsted acid sites, promoting the generation of ZnOH+ species. This not only suppressed the hydrogen transfer reaction but also significantly enhanced the dehydrogenation performance of the catalyst, improving the selectivity towards hydrogen. Additionally, the catalyst exhibited increased carbon capacity and reduced carbon deposition rate after hydrothermal treatment, demonstrating excellent anti-coking properties.

Synthesis of metal-free heteroatom (N, P, O, and B) doped biochar catalysts for enhanced catalytic co-pyrolysis of walnut shells and palm oil fatty acid distillate to produce high-quality bio-oil

In the current study, sugarcane bagasse-derived biochar catalysts were synthesized by doping with metal-free heteroatoms including nitrogen, phosphorus, oxygen, and boron and their efficacy was tested for catalytic co-pyrolysis of walnut shells (WS) and palm oil fatty acid distillate (PFAD) using Py-GC/MS. The biochar catalysts’ properties and their effectiveness on co-pyrolytic bio-oil (overall product distribution, selectivity towards aliphatic and aromatic hydrocarbons, and carbon number ranges) were extensively examined. Among the various catalysts considered, boron-doped biochar (BCB) demonstrated effective performance due to an improved surface area, porosity, and acidity and resulted in a significantly increased hydrocarbon yield, particularly in the gasoline and diesel range, and preference for aromatic over aliphatic hydrocarbons. The optimum bio-oil quality was achieved at a feedstock-to-catalyst ratio of 2:1 and a pyrolysis temperature of 750 °C, with a hydrocarbon yield of 90.8 % and aromatic hydrocarbon selectivity of 63.5 %. Overall, the study underscores the role of BCB in fostering deoxygenation, decarboxylation, and aromatic selectivity via thermal and catalytic pathways, highlighting the potential of non-metallic doped biochars for bio-oil upgrading.

Pyrolysis-catalysis of waste tire to enhance the aromatics selectivity via metal-modified ZSM-5 catalysts

Excessive untreated waste tires (WT) have posed threats to the environment and human health. Pyrolysis-catalysis, as a promising treatment technology, could convert WT into high-valued products such as pyrolysis oil. Moreover, BTX compounds (Benzene, toluene, and xylene) were important raw materials in the chemical industry. In order to sharply increase the BTX selectivity in the pyrolytic oil, transition metals (Ni and Fe) were impregnated on the ZSM-5 catalyst. Furthermore, this paper also explored the effect of catalysis modes, catalysts-to-feedstock mass ratios, and catalysis temperatures on the distribution of the aromatics in the WT pyrolysis-catalysis oil. The results suggested that the optimal operating parameters for BTX compound production with a selectivity of 39.87% were in-situ mode, catalysis temperature=600 °C, and catalyst-to-feedstock mass ratio=1:1 by applying Ni/ZSM-5. According to the GC-MS identification results, it proposed that the Diels-Alder reaction of isoprene and cracking and recombination of limonene in the aliphatic hydrocarbon pool were the main paths to generate the aromatics, while the addition of ethylene radicals in the monocyclic aromatic hydrocarbon (MAH) and polycyclic aromatic hydrocarbon (PAH) pools was dominant in the growth of the aromatics. The study provided a viable approach for upgrading WT to produce high-value aromatic products.