Search Results (327)

The selective conversion of high-molecular-weight paraffins (C₂₀–C₄₀) into linear alpha-olefins is often hindered by severe diffusion limitations and secondary over-cracking. This study addresses these challenges by transforming low-value natural minerals into sophisticated catalytic systems. We present a “top-down” engineering strategy for designing hierarchical catalysts based on natural Kazakhstani clinoptilolite. The multi-stage modification involves synergistic demineralization and precision chelation (EDTA, sulfosalicylic acid) to generate a tailored mesoporous architecture. This framework serves as a host for the sub-nanometric immobilization of Keggin-type heteropolyacids (PW₁₂, PMo₁₂), ensuring optimal active-phase dispersion. The innovative dual-step modification successfully bypassed the “micropore barrier”, creating a high-surface-area hierarchical network that facilitates the transport of bulky paraffinic molecules. Precise localization of heteropolyacid clusters within the created mesopores resulted in the formation of superstrong Lewis acid sites, as confirmed via temperature-programmed ammonia desorption. These sites triggered a highly efficient monomolecular beta-scission mechanism, suppressing undesirable hydrogen transfer reactions. The resulting catalysts achieved a breakthrough in technical paraffin cracking, delivering a 70% liquid product yield with an unprecedented >50% selectivity toward the C₇–C₁₄ α-olefin fraction. This work demonstrates a sustainable pathway for upgrading natural zeolites into high-performance, green catalysts that rival expensive analogs in precision and efficiency. Full article

This study investigates the influence of isomorphous substitution of Aluminum by V, Zr, La, and Ni in Beta zeolite frameworks used as supports for Ni-based dry reforming of methane catalysts. The research focuses on how the nature of the incorporated metal affects catalytic activity and long-term stability. Catalysts were synthesized using both co-impregnation and sequential impregnation strategies. Physicochemical characterization—including gas adsorption, X-ray diffraction, transmission electron microscopy, and H₂ temperature-programmed reduction—revealed distinct structural roles for each metal. Results indicate that V primarily occupies T-vacancy sites within the dealuminated Beta framework, whereas Ni resides as charge-compensating extra-framework species or highly dispersed NiO clusters. Zr and La tend to form highly dispersed oxide species or occupy enlarged silanol nests. Notably, the addition of La₂O₃ was found to significantly enhance the long-term stability of the catalysts during the dry reforming of methane process. V-modified catalysts exhibited the highest activity but suffered from low stability; conversely, Zr incorporation offered the best overall performance, balancing high activity with enhanced stability, achieving 85% CO₂ and 75% CH₄ conversion, with no detectable carbon deposition after 98 h on stream. Full article

The fast growth of the aviation sector has intensified the need for sustainable alternatives to conventional fossil-based jet fuels. Sustainable aviation fuel (SAF) has emerged as one of the most promising strategies to reduce greenhouse gas emissions while remaining compatible with existing aviation infrastructure. Among the different feedstocks explored for SAF production, lipid-based resources such as vegetable oils, animal fats, and waste cooking oil have received considerable attention due to their high content of triglycerides and free fatty acids. Additionally, the increasing generation of plastic waste has stimulated interest in its catalytic valorization as an alternative carbon source for hydrocarbon fuel production. This mini-review summarizes recent advances in catalytic pathways for producing jet-fuel-range hydrocarbons (C₈–C₁₆) from lipid-based feedstocks and polyolefins. Particular emphasis is given on hydroprocessing reactions, including deoxygenation, cracking, and isomerization, which are essential to adjust fuel properties and meet aviation specifications. In this context, bifunctional heterogeneous catalysts play a crucial role, particularly regarding the influence of the metal phase and catalyst support on catalytic activity and stability. Different support classes, including metal oxides, mesoporous silicas, and zeolites, are discussed. Carbon-based materials, especially carbon nanotubes (CNT), are also highlighted due to their outstanding chemical and textural properties. Full article

Here, we report a highly efficient and stable catalytic system based on monometallic oxides supported on HY zeolites for the catalytic oxidation of chlorobenzene (CB). Among the transition and rare-earth metal oxides screened, the 30Cu/HY catalyst demonstrates exceptional performance, achieving near 100% CB conversion at 300 °C (500 ppm CB, 10,000 h⁻¹) alongside outstanding 24 h continuous stability without deactivation. Quantitative Py-IR analysis reveals that this superior activity is fundamentally driven by extensive solid-state ion exchange, forming robust Lewis acid centers (Cu-Y structures) that synergize with zeolitic Brønsted acid sites to efficiently polarize and cleave C-Cl bonds. Through an integrated approach combining in situ DRIFTS, real-time mass spectrometry, TGA, and NLDFT pore size analysis, we elucidate that the exceptional deep-oxidation capability of Cu/HY continuously mineralizes carbonaceous intermediates. This property minimizes coke deposition (2.91 wt%) and preserves the hierarchical pore architecture, preventing the coverage of active sites and severe pore blockage by partially oxidized intermediates (such as phenolic, aldehydic, and quinonic species) and stable carbonate species responsible for the deactivation of other metal oxides. These insights provide a mechanistic framework for the rational design of robust, chlorine-resistant catalysts for the sustainable abatement of persistent organic pollutants. Full article

N₂O (Nitrous oxide) is a potent greenhouse gas with a global warming potential nearly 300 times that of CO₂ and poses a critical environmental challenge, particularly in semiconductor and display manufacturing, where it is emitted during plasma processes. However, catalytic N₂O abatement in O₂-rich environments remains inefficient because O₂ competitively occupies active sites and hinders the turnover of surface oxygen species. To clarify how support properties govern this inhibition, Co-based catalysts supported on beta zeolite, CeO₂, and TiO₂, together with unsupported Co₃O₄, were comparatively evaluated for direct N₂O decomposition. Among them, Co/Beta exhibited the highest performance, achieving >95% N₂O conversion at 450 °C in the presence of 5% O₂ with excellent long-term stability. Co/Beta possessed a high specific surface area (649 m² g⁻¹) and a mesoporous framework that favored uniform Co dispersion and reactant accessibility, while its high Co²⁺/(Co²⁺ + Co³⁺) ratio (75.5%) and large fraction of chemisorbed oxygen species (79.9%) promoted oxygen-vacancy formation and facile oxygen exchange. These results indicate that the ability of Co/Beta to maintain high activity in the presence of oxygen stems from support-modulated cobalt surface states and enhanced oxygen turnover behavior. These findings provide a support-design principle for stable N₂O decomposition under oxygen-containing exhaust conditions. Full article

The co-pyrolysis of Chlorella vulgaris (CV) and Eucalyptus branches (EP) offers a promising strategy to enhance bio-oil yield, improve resource utilization efficiency, and alleviate environmental pressures. In this study, the microwave-assisted co-pyrolysis of CV and EP at a mass ratio of 2:1 was investigated, focusing on the catalytic performance of Ni-X (X = Mg, Cu, Fe) bimetallic modified HZSM-5 zeolites. The effects of these catalysts on pyrolysis characteristics, product distribution, and bio-oil composition were systematically evaluated. Experimental results showed that the 15% Ni-Cu/HZSM-5 catalyst exhibited the best catalytic performance, achieving the highest bio-oil yield of 16.83%; it also elevated the R_m to 0.0687 wt.%/s and reduced T_s to 2084 s. Composition analysis revealed that Ni-Cu/HZSM-5 significantly promoted the formation of hydrocarbons, increasing their relative content from 11.59% (C2E1 Group) to 28.92%, while effectively suppressing the formation of nitrogen-containing compounds, reducing their content by 5.05%. Based on these results, a possible reaction pathway is proposed in which the Ni-Cu/HZSM-5 catalyst may enhance heteroatom removal through hydrodeoxygenation (HDO) at the Ni-Cu sites, followed by cracking and aromatization at the HZSM-5 acid sites. This effect may be complemented by preferential adsorption of oxygenated intermediates over nitrogen-containing species, which could help suppress the formation of nitrogenous heterocycles. This work provides theoretical guidance for the application of bimetallic zeolite catalysts in microalgae/lignocellulose co-pyrolysis, alongside a viable pathway for valorizing Eucalyptus by-products to produce high-quality bio-oil. Full article

Biodiesel is a sustainable and promising alternative energy source produced from renewable raw materials using various methods. One effective approach is simultaneous esterification and transesterification, which relies on suitable catalysts that can be either homogeneous or heterogeneous. Homogeneous catalysts (acid or base) offer high activity but are corrosive and difficult to recover, necessitating energy-intensive processes such as aqueous quenching and neutralization, which can lead to soap formation and stable emulsions. By comparison, heterogeneous catalytic systems overcome many of these challenges due to their ease of recovery, reusability, and simplified product separation, which collectively enhance economic viability and environmental sustainability. This review highlights recent progress in the application of zeolite-based solid catalysts for biodiesel synthesis, with particular emphasis on their use in converting waste cooking oil and other low-cost feedstocks, including non-edible oils, non-food biomass sources, algal resources, and genetically engineered microorganisms. Key factors such as catalytic activity, selectivity, catalyst loading, and reusability are discussed, highlighting the advantages of zeolites due to their unique crystal structure, high thermal stability, and ease of product recovery. Overall, this review underscores the challenges and opportunities in zeolite-based catalysis to provide a comprehensive understanding of its potential to enhance the efficiency and scalability of biodiesel production. Full article

Ammonia is indispensable to the fertilizer and chemical industries, yet its manufacture still relies predominantly on the energy-intensive Haber–Bosch process operated at 400–500 °C and 150–250 bar, with a substantial carbon footprint. Single-atom catalysts (SACs) and sub-nanometric clusters have recently emerged as promising alternatives for thermocatalytic ammonia synthesis under milder conditions because they maximize metal utilization and enable precise control of the active site environment. This review first summarizes how the transition from conventional Fe and Ru nanoparticles to isolated or few-atom sites fundamentally alters the kinetic landscape, favoring associative N₂ activation pathways that lower apparent activation energies and alleviate H₂ poisoning. We then discuss Ru-based SACs and SAAs supported on zeolites, carbons, ceria, and MXenes, highlighting how strong metal–support and promoter interactions, tandem single-atom/nanoparticle motifs, and alloying strategies tune N₂ and H₂ binding to deliver high NH₃ productivities at 200–400 °C and ≤30 bar. In parallel, we review emerging non-noble systems based on Fe and Co, including high-loading Fe–N₄ sites prepared via MOF-derived post-metal-replacement routes and Co single atoms or Co₂ clusters on N-doped carbons, which already rival or surpass Ru benchmarks under similar conditions. Collectively, these studies show that tailoring the number of atom metal sites, coordination, and support polarity around isolated metal sites provides a useful tool to mitigate some aspects of volcano and scaling-relation limitations, indicating that SACs could contribute to low-temperature ammonia synthesis when combined with appropriate process design. Full article

This paper systematically reviews the recent advances in catalytic systems and reaction mechanisms for the synthesis of crotonaldehyde via aldol condensation using acetaldehyde as the feedstock. Firstly, the structural characteristics, reactivity, and important applications of crotonaldehyde in fine chemicals are outlined, with particular emphasis on the limitations of traditional homogeneous base-catalyzed processes, such as difficulty in separation and environmental pollution caused by waste streams. On this basis, heterogeneous catalytic systems are discussed in detail, focusing on the progress of metal oxides, aluminosilicate zeolites, and heteroatom zeolites in regulating acid–base properties, active site structures, and reaction pathways. Furthermore, the typical carbanion mechanism and direct condensation mechanism in aldol condensation are summarized, and the catalyst deactivation and by-product formation mechanisms are analyzed. Finally, perspectives on the construction of efficient and green catalytic systems and future research directions are proposed, aiming to provide theoretical guidance for process optimization and catalyst design in crotonaldehyde synthesis from acetaldehyde. Full article

The catalytic upgrading of vacuum residue (VR) is constrained by the high cost, diffusional limitations, and rapid deactivation of conventional zeolite-based catalysts due to severe coking. Addressing this, we developed novel, low-cost, and coke-resistant catalysts utilizing naturally abundant Iraqi kaolin. A composite support comprising 80 wt.% Iraqi red kaolin and 20 wt.% white kaolin was synthesized via thermal activation at 800 °C and acid leaching. This support was subsequently impregnated with transition and rare-earth metals (Ni, Co, Ce) at 3–40 wt.% loadings, and comprehensively characterized using XRD, BET, SEM-EDX, and XPS. Catalytic performance was evaluated during VR upgrading in a fixed-bed batch reactor at 450 °C. Among the formulations, the 20 wt.% Ce-loaded catalyst (MKRW-800A@Ce20%) exhibited superior efficiency, achieving 80.15% VR conversion, 61.04% liquid yield, and minimal coke formation (3.81 g) compared to Ni and Co counterparts. This enhanced activity is attributed to synergistic effects of improved surface acidity, textural accessibility, and the Ce³⁺/Ce⁴⁺ redox couple, which promotes selective cracking while suppressing coke precursors. These findings provide new insights into the rational design of natural clay-based catalysts, establishing Ce-modified metakaolin as a viable, sustainable alternative to zeolites for industrial heavy-oil processing. Full article

Utilizing the pyrolysis reaction of endothermic hydrocarbon fuels to provide thermal protection for hypersonic vehicles is a feasible approach. The introduction of catalysts or cracking-initiating additives could promote hydrocarbon fuel cracking and increase the reaction heat sink. Catalysts such as ZSM-5 zeolite, Al₂O₃, and precious metals were commonly used for hydrocarbon fuel cracking. By optimizing their pore structure and acidity, their catalytic cracking performance can be effectively improved. These catalysts can function not only as catalytic coatings but also be dispersed in the fuel to act via quasi-homogeneous catalytic cracking. Additionally, small-molecule and macromolecular additives could crack at lower temperatures to generate active free radicals, thereby initiating the cracking of hydrocarbons and increasing the reaction heat sink. Under the conditions of a reaction temperature of 650–750 °C, a pressure of 3–5.5 MPa, and a fuel flow rate of 1 g/s, quasi-homogeneous catalysts can enhance the heat sink of hydrocarbon fuel cracking by 5–21%, while cracking-initiating additives can enhance it by 5.6–8.6%. Therefore, based on the different action modes of catalysts or additives, this review summarizes the recent research on improving the cracking of endothermic hydrocarbons from three aspects: coating catalysts, quasi-homogeneous catalysts, and cracking-initiating additives. Subsequently, the potential challenges of each approach in practical applications are analyzed. Furthermore, based on the current research findings, we outline future research directions with the expectation of facilitating the advancement of efficient cracking technologies for endothermic hydrocarbons. Full article

The oxygen evolution reaction (OER), a key half-reaction in electrochemical water splitting, is limited by sluggish multi-electron transfer kinetics, starting extensive research into efficient, low-cost nanoscale electrocatalysts, particularly those based on nickel, cobalt, and iron, as well as mixed-metal, hybrid, and heteroatom-doped carbon-based metal-free systems, as presented here. Ni- and Co-based electrocatalysts show high efficiency for alkaline OER due to optimized nanostructures, surface modifications, heterostructure design, and multi-metal doping, which enhance activity, stability, and electronic properties. Their performance relies on precise atomic-level control of structure and synergistic interactions, enabling them to approach or rival noble-metal catalysts. Iron-based electrocatalysts are also promising due to their abundance, low cost, and flexible redox chemistry, forming active iron oxyhydroxide species during operation; however, their low conductivity requires structural and electronic optimization. Beyond Fe, Ni, and Co, copper-based compounds, zeolitic imidazolate framework-derived structures, and manganese phosphide–cerium oxide composites offer enhanced oxygen vacancies, tunable structures, and strong interfacial synergy. Furthermore, heteroatom-doped carbon materials incorporating nitrogen, phosphorus, or sulfur improve catalytic activity by modifying electronic structure, creating active sites, and enhancing charge transfer. Overall, careful control of composition, structure, and electronic properties enables the development of efficient, durable, and scalable noble-metal-free catalysts for OER. Full article

CO₂-assisted catalytic pyrolysis presents a viable and promising approach to addressing plastic waste pollution and mitigating climate change. However, the effects of the metal–catalyst combination mode and the spatial distance between metal–acid sites on catalytic performance remain unclear. In this study, the reaction behaviors of the configurations, Fe₃O₄ and ZSM-5 in tandem catalysis (Fe₃O₄&HZ), their physical mixture (Fe₃O₄-HZ), and Fe-loaded ZSM-5 (Fe/HZ), were compared in polypropylene pyrolysis under a CO₂ atmosphere. The aromatic contents followed this order: Fe/HZ > Fe₃O₄-HZ > Fe₃O₄&HZ > ZSM-5 > Fe₃O₄. Specifically, Fe/HZ with the highest degree of metal–zeolite proximity achieved an aromatic content of 66.1%, significantly higher than the 34.2% obtained with Fe₃O₄&HZ, demonstrating that closer metal–acid proximity promoted aromatic formation. Moreover, Fe/HZ significantly reduced coke deposition. Based on characterization results from XRD, SEM, TEM, XPS, and NH₃-TPD, the enhanced spatial proximity between metal and acid sites strengthened the functional synergy between iron-based redox sites and zeolitic Brønsted acid sites. This synergy facilitated the reverse water–gas shift reaction of CO₂, which consumed hydrogen generated during aromatization and shifted the reaction equilibrium toward enhanced aromatic production. These findings would offer theoretical and strategic insights into the optimization of CO₂-assisted catalytic pyrolysis systems for the sustainable upcycling of plastic waste. Full article

Linear alkylbenzene (LAB) is the main raw material used to make biodegradable detergents, and its production process is based on aromatic alkylation. HY zeolites that have undergone controlled dealumination and desilication have led industrial standards amongst solid acid catalysts because of their controllable acidity and hierarchical pore structure. Coke formation in such systems can assume a dual role, which is dependent on its condition. Though the over-deposition is known to cause deactivation by blocking the micropores, Bronsted acid-site masking, and diffusion collapse, the low-level deposition could also be done to increase the monoalkylate selectivity by the pore mouth catalysis, steric modulation, and selective suppression of secondary alkylation pathways. The critical review is done on the structural-kinetic interaction that determines the coke evolution in HY-based catalysts. In order to moderate the acid-site density and enhance hydrothermal stability, dealumination (Si/Al optimization of about 2.5 to 30–100) occurs, but to reduce deep-pore coke formation, desilication (interconnected mesopores) is created. The bimodal porosity and regulated acidity are found to be synergistic, as hierarchical HY zeolites produced through successive cycles of steam and alkaline treatments not only show LAB selectivity in excess of 90% but also exhibit much longer catalyst lifetimes. Quantitative research on the beneficial coke regime revealed that it was composed of about 36 wt% hydrogen-rich species, which were localized at the pore mouths, hence enhancing monoalkylation selectivity by 15–40%. Beyond a critical transition window (e.g., 8–12 wt.%), coke formation to condensed polyaromatic and graphitic products leads to fast deactivated coke formation, which is due to percolation limits and transport-controlled kinetics. More advanced techniques of characterization of the coke, e.g., temperature-programmed oxidation (TPO), ²⁷Al MAAS NMR, and UV-Raman spectroscopy, indicate how the coke is changed to highly structured graphitic deposits of high oxidation activation energy. Activity recovery of 85–98% is obtained in regeneration processes, including controlled oxidative calcination, microwave-based and plasma-based processes, and thermal management protocols, and it would be determined by the chemistry of the coke, its spatial distribution, and the regeneration protocols. This paper has developed a mechanistic coke control system by cross-tuning the acidity and development of an effective pore network, which led to a sustainable aromatic alkylation reaction with minimal activity loss, high selectivity, and long life. Full article

The environmental concerns associated with the excessive use and improper disposal of plastic waste have led to increased interest in chemical recycling methods such as pyrolysis. In this study, waste plastic pyrolysis oil (WPPO) was evaluated as a potential feedstock to produce high-quality feedstock for lubricant base oils through hydroprocessing. WPPO was obtained via the thermal degradation of waste plastic at 400 °C under a nitrogen atmosphere using a 2 t/day pyrolysis reactor. The physicochemical properties of WPPO were analyzed, including the sulfur, chlorine, and metal contents. A series of Pt-supported catalysts based on different acidic supports (SAPO-11, SAPO-34, and Zeolite Y100) was prepared using an incipient wetness impregnation method and characterized by BET, XRD, and TPD techniques. The hydroprocessing reactions were conducted under varying temperature and pressure conditions to evaluate conversion and optimize product selectivity. The catalysts exhibited different surface areas, pore structures, and acidity profiles, which directly impacted their hydroprocessing performance. The results demonstrate that Pt/Y-100 exhibited the best upgrading performance among the tested catalysts, achieving an olefin-to-paraffin conversion of over 88.65% with a dominant paraffinic hydrocarbon distribution in the C15–C25 range under optimal conditions (300 °C and 40 bar). The results demonstrate that the conversion of olefins to paraffins in WPPO can be effectively controlled by tuning the reaction conditions and catalyst. Full article