Zeolite Catalysts Research Articles

Insight into the Key Role of Yttrium Modification for the Enhanced Hydrothermal Stability over Y-Cu-SSZ-39 Zeolite Catalysts

Insight into the Key Role of Yttrium Modification for the Enhanced Hydrothermal Stability over Y-Cu-SSZ-39 Zeolite Catalysts

The Impact of Support and Reduction Temperature on the Catalytic Activity of Bimetallic Nickel-Zirconium Catalysts in the Hydrocracking Reaction of Algal Oil from Spirulina Platensis

The aim of this work was to investigate the hydrocracking of algae oil derived from Spirulina Platensis species catalyzed with bi-component nickel-zirconia catalysts supported onto different carriers (BEA, ZSM-5 and Al2O3) in an autoclave at 320 °C for 2 h with a hydrogen pressure of 75 bar. All catalysts were prepared using the wet co-impregnation method and were characterized by H2-TPR, XRD, NH3-TPD, BET and SEM-EDS. Before reactions, catalysts were calcined at 600 °C for 4 h in a muffle furnace, then reduced with 5%H2-95%Ar reducing mixture at 500 °C, 600 °C or 700 °C for 2 h. The obtained products were analyzed and identified by HPLC and GC-MS techniques. In addition to the investigation of the support effect, the influence of the reduction temperature of catalytic systems on the catalytic activity and selectivity of the products was also examined. The activity results show that Ni-Zr systems supported on zeolites exhibited high conversion of algal oil. A gradual decrease in conversion was observed when increasing the reduction temperature of the catalyst (from 500 °C to 600 °C and 700 °C) for BEA zeolite catalysts. The reaction products contain hydrocarbons from C7 to C33 (for zeolite-supported catalysts) and C36 (for systems on Al2O3). The identified hydrocarbons mainly belong to the gasoil fraction (C14–C22). In the research, the best catalyst for the algal oil hydrocracking reaction was found to be the 5%Ni-5%Zr/BEA system reduced at 600 °C, which exhibited the second highest algal oil conversion (94.0%). The differences in catalytic activity that occur are due to the differences in the specific surface area among the supports and to differences in the acidity of the catalyst surface depending on the reduction temperature.

Co‐feeding CO2 for Methylfuran Aromatization over Bifunctional Zeolite‐supported ZnMoO4

Aromatization of biofuran offers promising approaches for sustainable biochemical production. However, this process is often hampered by low yields and severe coking on traditional zeolite catalysts. Herein, we report co‐feeding CO2 for 2‐methylfuran (MF) aromatization (CCMA) over bifunctional ZSM‐5 supported ZnMoO4. This bifunctional catalyst can achieve both MF and CO2 conversions of >97%, generating >85% carbon yield of target arenes and CO with negligible alkenes (0.05%). Meanwhile, coke formation is remarkably suppressed from 22.3% to 8.6%. ZnMoO4/ZSM‐5 is capable of selectively manipulating the reaction intermediates and pathways of the CCMA reactions, favoring the cyclopentenones‐ and alkenes‐based dehydro‐aromatization rather than the benzofurans‐based pathway. This finding challenges the prevailing understanding that MF aromatization follows a hydrocarbon pool mechanism. Moreover, the abundant surface oxygen vacancies of ZnMoO4 facilitate the adsorption of CO2 and its subsequent reaction with coke. These insights into reaction mechanism and catalyst design for co‐conversion of CO2 and biofuran can offer guidelines for process intensification in biomass utilization with a carbon‐negative manner.

Co-feeding CO2 for Methylfuran Aromatization over Bifunctional Zeolite-supported ZnMoO4.

Aromatization of biofuran offers promising approaches for sustainable biochemical production. However, this process is often hampered by low yields and severe coking on traditional zeolite catalysts. Herein, we reportco-feeding CO2 for 2-methylfuran (MF) aromatization (CCMA) over bifunctional ZSM-5 supported ZnMoO4. This bifunctional catalyst can achieve both MF and CO2 conversions of >97%, generating >85% carbon yield of target arenes and CO with negligible alkenes (0.05%). Meanwhile, coke formation is remarkably suppressed from 22.3% to 8.6%. ZnMoO4/ZSM-5 is capable of selectively manipulating the reaction intermediates and pathways of the CCMA reactions, favoring the cyclopentenones- and alkenes-based dehydro-aromatization rather than the benzofurans-based pathway. This finding challenges the prevailing understanding that MF aromatization follows a hydrocarbon pool mechanism. Moreover, the abundant surface oxygen vacancies of ZnMoO4 facilitate the adsorption of CO2 and its subsequent reaction with coke. These insights into reaction mechanism and catalyst design for co-conversion of CO2 and biofuran can offer guidelines for process intensification in biomass utilization with a carbon-negative manner.

Catalytic Cracking of Liquefied Petroleum Gas (LPG) to Light Olefins Using Zeolite-based Materials: Recent Advances, Trends, Challenges and Future Perspectives.

The catalytic cracking of liquefied petroleum gas (LPG) has attracted significant attention due to its importance in producing valuable feedstocks for the petrochemical industry. This review provides an overview of recent developments in zeolite-based catalyst technology for converting LPG into light olefins. Catalytic cracking utilizes zeolite-based catalysts usually associated with stability challenges, such as coking and sintering. The discussion focused on the underlying mechanisms that govern the catalytic cracking process and provided insights into the complex reaction pathways involved. A comprehensive analysis of various strategies employed for improving the effectiveness of zeolite catalysts has been discussed in this review. These strategies encompass using transition metals to modify catalyst properties, treatments involving phosphorous modification, alkaline earth metals, and alkali metals to alter the acidity level of the zeolites. The elucidation of the impact of silica-to-alumina ratios in zeolites and the development of hierarchical zeolite-based catalysts through top-down and bottom-up methodologies are also discussed.

A high-efficient beta-zeolitic catalyst for conversion of waste cooking oil towards biodiesel

The conversion of waste cooking oil into biodiesel can bring about dual benefits: alleviating environmental pollution and realizing waste recycle. Embryonic zeolite has highly accessible acid sites because of the partially formed or more open zeolitic structure, which can solve problems such as diffusion limitation and inaccessible acid sites that the traditional zeolite catalysts face in the process of macromolecular reactants. In this work, a series of embryonic Beta zeolites were prepared by using mesoporous SBA-15 as a self-sacrificial silica source via a solid-state transformation strategy. NH3-TPD and FT-IR pyridine adsorption confirm that Brønsted acid sites have been created in these amorphous form embryonic catalysts. The diffusion property of toluene obtained by a zero-length column method proved that the higher the zeolization degree, the greater the diffusion activation energy. The synergistic effects resulted from the combination of the ordered mesoporous structures (ranging from 2 to 10 nm) stemming from the SBA-15 substrate and the moderate acid sites (∼88 μmol g−1) offered the embryonic SBEA-3 catalyst with remarkable catalytic performance for ≥95 % conversion during 20 times cycling tests and more than 90 % methyloleate yield.

A Computational Mechanistic Study on Copper Autoreduction in Cu-CHA Zeolite Catalysts.

The activation of Cu-zeolite catalysts is accompanied by an autoreduction reaction, in which a part of Cu(II) species is spontaneously reduced to Cu(I) species. The stoichiometry of autoreduction in which the release of one O2 is accompanied by the reduction of four Cu(II) to Cu(I) has been proposed, but the detailed mechanism of this autoreduction remains unclear. In this work, we used DFT calculations to study the autoreduction mechanism in Cu-CHA zeolites. The two reduction mechanisms of [CuOH]+ to Cu+ in CHA-type zeolite were systematically studied. In Mechanism I, two [CuOH]+ react via dehydration to form [Cu-O-Cu]2+, and the further reaction of two [Cu-O-Cu]2+ to produce O2 is the most critical step, which requires four charge-compensating framework Al in close proximity. In Mechanism II, the production of O2 occurs via [CuO]+ intermediates, and the generation of possible [CuO]+ is the most critical step. The exploration of autoreduction reactions in a variety of Cu-CHA models with different Al sittings shows that the O-O distances between two intermediate precursors, i.e., two [Cu-O-Cu]2+ in Mechanism I, or two [CuO]+ in Mechanism II, are key factors determining the activation barriers of O2 production during autoreduction.

Sonochemical Preparation of Fe-Y Zeolite Catalyst for the Conversion of Benzene to Phenol

Enzyme-mimetic materials such as Fe-containing zeolites are of research interest due to the high selectivity for the one-step selective oxidation of benzene to phenol over the Fe-catalytic active center at room temperature and ambient pressure. This study investigates a Fe-modified Y zeolite catalysts prepared via a sonochemical method for the oxidation of benzene-to-phenol using water as solvent. These catalysts were subjected to a screening and optimization experiment by a response surface methodology (RSM), evaluating their potential for the synthesis of phenol. Achieving the preparation of a catalyst with an increased phenol selectivity from 3% to ~91% and almost 100% when evaluated at 30 ºC. Various Fe species, including the α-Fe(II) active site, were detected using UV-Vis spectroscopy, FTIR spectroscopy, and magnetic thermal gravimetric analysis (MTGA). Highlighting the potential of sonochemistry for preparing at mild temperatures (<100 ºC) iron-modified zeolite Y catalysts with room temperature catalytic active in water-based systems.

Extra-framework cations promoted zeolite-encaged cobalt catalysts towards efficient ethylbenzene dehydrogenation

The transformation of ethylbenzene to styrene through direct dehydrogenation is essential process in chemical industry, indispensable for the synthesis of polymers and plastics. Herein, faujasite zeolite encaged cobalt catalyst with potassium ion as the extraframework cations, namely K-Co@Y, is reported to be a robust catalyst for ethylbenzene direct dehydrogenation, showing ethylbenzene conversion of ∼45 % and styrene selectivity of ∼95 % simultaneously under employed conditions. The superior performance of K-Co@Y in comparison with Na-Co@Y is attributed to the effective modulation of zeolite-encaged Co2+ species by extraframework K+ ions, which increases the electron density of cobalt sites and facilitates CH bond activation. Although coke deposits cause gradual deactivation, the structural integrity of K-Co@Y can be well preserved during the dehydrogenation reaction and the performance can be full restored via a simple calcination regeneration step, making K-Co@Y an eligible catalyst for long-term running in the continuous regeneration mode. This study highlights the vital role of extraframework cations in zeolite-encaged single-site catalysts for target chemical transformations and opens up a new way to modulate the performance of zeolite catalysts.

The effect of pore structure on the local and nanoscale mobility of anisole and guaiacol in commercial zeolite catalysts

The effect of pore structure on the local and nanoscale mobility of anisole and guaiacol in commercial zeolite catalysts

Solid-state synthesis of aluminophosphate-based zeotypes from conventional amorphous precursors: Strategy and catalytic performance

Exploring novel strategies for the preparation of zeolitic materials with high performance continues to be of great significance. Here we report a general solid-state approach for fabricating aluminophosphate (AlPO)-based zeotypes by directly calcining conventional amorphous precursors at 300 °C for just 30 min. Accordingly, AEL, AFI, LTA and CHA types of AlPO-based zeotypes with high crystallinity and similar textural properties to those of counterparts made by established synthesis approaches have been synthesized. As a demonstration, the catalytic performance of Mg-substituted AlPO-11 (S-MgAlPO-11) in hydroisomerization of n-hexadecane (n-C16) was also investigated. Compared with the Pt supported on conventional MgAlPO-11 (Pt/C-MgAlPO-11) catalyst, the Pt/S-MgAlPO-11catalyst exhibits higher isomerized (87 % vs. 84 %), multi-branched C16 (48 % vs. 30 %) yields and superior reaction stability, attributing to the improved diffusion property and appropriate metal-acid balance. This strategy provides an efficient approach to synthesis promising zeolitic catalysts for industrial applications.

Biodiesel Synthesis from Calophyllum Inophyllum Utilizing Modified Zeolite and Bentonite Catalysts

Biodiesel Synthesis from Calophyllum Inophyllum Utilizing Modified Zeolite and Bentonite Catalysts

Oxidative Aromatization of Ethane

This study is focused on examining the incorporation of oxidative dehydrogenation into the aromatization of ethane, utilizing thermodynamic analysis and catalytic experiments. The catalysts were characterized by inverse temperature programmed reduction, X‐ray photoelectron spectroscopy (XPS) and X‐ray diffraction (XRD). The results indicated that a blend of the M1 catalyst, containing oxides of vanadium, niobium, and tellurium, with H‐ZSM‐5, serves as an effective catalyst system for the oxidative aromatization of ethane at T = 380 °C. The M1's role in the oxidative dehydrogenation of ethane contributes to de‐bottlenecking the essential step of the reaction. On the zeolitic catalyst aromatic compounds are formed from a surface hydrocarbon pool. In parallel, the oxidation of these intermediates was observed. Also, the formation of paraffins through H‐transfer was evident from the catalytic results. While the zeolite underwent significant deactivation due to coking, the M1 catalyst demonstrated highly stable activity. Interestingly, the system did not show any synergistic effects. Based on the structure‐activity relation of the catalytic system a reaction mechanism is proposed.

Core–Shell-Structured Ni/ZSM-5@Silicalite-1 Zeolite Catalyst with a High Catalytic Performance for Ethylene to Propylene Reaction

Core–Shell-Structured Ni/ZSM-5@Silicalite-1 Zeolite Catalyst with a High Catalytic Performance for Ethylene to Propylene Reaction

Kinetic Model of the Synthesis of Methyl-tert-Butyl Ethers in the Presence of HY and CuBr2/HY Zeolite Catalysts

Kinetic Model of the Synthesis of Methyl-tert-Butyl Ethers in the Presence of HY and CuBr2/HY Zeolite Catalysts

Heteropolyacids combined with Y zeolite as superior solid acid catalysts to accelerate lactic acid esterification

AbstractBACKGROUNDEthyl lactate produced via esterification between lactic acid and ethanol can be used in plastics, polymers and food industries and renowned for its biodegradability and low toxicity. However, lactic acid self‐catalyzed esterification presents a slow reaction process, and acid catalysts are needed to improve the catalysis. Homogeneous acid catalysts like H2SO4 are corrosive, as well as being difficult to be seperated from the reaction media; therefore, advanced heterogeneous catalysts are more ideal. In this study, two kinds of heteropolyacid–zeolite catalysts, involving loading silicotungstic acid and phosphotungstic acid onto Y zeolite, were synthesized, characterized using X‐ray diffraction, NH3 temperature‐programmed desorption and scanning electron microscopy and analyzed for their catalytic efficiency in the catalytic esterfication.RESULTSResults showed that the Keggin structures of heteropolyacids were retained during the preparation process and strong acid sites of Y zeolite were enriched, which made the main contribution to the esterification of lactic acid and ethanol. Furthermore, the initial‐stage reaction rate of esterification was significantly enhanced. During the first hour of esterification, the conversion of lactic acid increased from 18% to 65%. Exp Dec1 index model was employed to determine the activation energies of 60HSiW‐Y and 60HPW‐Y, which exhibit values of 29.3 and 28.2 kJ mol−1, respectively.CONCLUSIONThis study indicates that Keggin structures of heteropolyacids play a key role in the esterification and heteropolyacid–zeolite catalysts can effectively catalyze the esterification. Meanwhile, the results of the kinetic experiments can be of reference significance for large‐scale industrial processes involving esterification. © 2024 Society of Chemical Industry (SCI).

Regioselective encapsulation of Pd clusters in hollow polycrystalline shell

Zeolite catalysts have been widely applied in petroleum and chemical industries. Nano/hierarchical structure could improve the utilization efficiency of active sites, especially for metal species encapsulated in zeolites. However, the uniformity of zeolite surface and crystallinity would decrease, leading to low stabilization effect. Herein, we developed a seed-directed method to prepare Pd clusters (∼1.3 nm) regioselectively encapsulated in hollow polycrystalline shell of Silicalite-1 zeolite. In nitrobenzene hydrogenation reaction, the optimized Pd@S-1-hp showed a high conversion of 92.2 % at 110 °C, which is 40 % higher than that of Pd clusters in bulk zeolite. Sub-nano Pd species in polycrystalline shell could significantly shorten the diffusion length on the basis of strong microporous confinement effect. Catalytic hydrogenation activity remained stable after six cycles. This structure could be extended to heterogeneous reactions suffering from diffusion limitation.

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.

Exploring the Morphological Effect of Zeolite Beta on Catalytic Cracking of Polyethylene.

Two types of zeolite catalysts, namely, nanosized Beta-N and micrometer-sized Beta-M, were used to crack low-density polyethylene (LDPE) with three different molecular weights: 4000, 200,000, and 3,000,000. The structural and acidic properties were analyzed by N2 physisorption, transmission electron microscopy, X-ray diffraction, temperature-programmed desorption of isopropylamine (IPA-TPD), and pyridine-adsorbed FTIR. The catalytic activity was tested at 623 K and 3.5 N2 MPa in an autoclave batch reactor for PE cracking. High Mw PE required higher decomposition activation energy due to transfer limitation. Beta-N showed better activity in PE cracking than Beta-M, with PE conversion of 82.7 and 62.0% for Beta-N and Beta-M, respectively. In addition, the nanosized Beta-N exhibited quite lower activation energy of catalytic PE decomposition than Beta-M, obtained by the Kissinger method in TGA measurement. The characterization results demonstrated that the Beta-N has abundant interparticulate mesopores to provide better dispersion for the catalysts into PE melt and the proximity of the cracking active sites. These results revealed that the Beta-N catalyst shows superior activity for the cracking of polyolefins.

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.