Active Sites and Induction Period of Fe/ZSM-5 Catalyst in Methane Dehydroaromatization

Solvent-Free Synthesis Enables Encapsulation of Subnanometric FeOx Clusters in Pure Siliceous Zeolites for Efficient Catalytic Oxidation Reactions

Metal/metal oxide clusters possess a higher count of unsaturated coordination sites than nanoparticles, providing multiatomic sites that single atoms do not. Encapsulating metal/metal oxide clusters within zeolites is a promising approach for synthesizing and stabilizing these clusters. The unique feature endows the metal clusters with an exceptional catalytic performance in a broad range of catalytic reactions. However, the encapsulation of stable FeOx clusters in zeolite is still challenging, which limits the application of zeolite-encapsulated FeOx clusters in catalysis. Herein, we design a modified solvent-free method to encapsulate FeOx clusters in pure siliceous MFI zeolites (Fe@MFI). It is revealed that the 0.3-0.4 nm subnanometric FeOx clusters are stably encapsulated in the 5/6-membered rings intersectional voids of the pure siliceous MFI zeolites. The encapsulated Fe@MFI catalyst with a Fe loading of 1.4 wt % demonstrates remarkable catalytic activity and recycle stability in the direct oxidation of methane, while also promoting the direct oxidation of cyclohexane, surpassing the performance of conventional zeolite-supported Fe catalysts.

Direct synthesis of Fe-aluminosilicates from red mud for catalytic deoxygenation of waste cooking oil

Conversion of red mud (RM) that contains a high level of silica, alumina and iron minerals into heterogenous catalysts, offers a route for the utilization of abundant toxic by-products of bauxite refining. In this study, the conversion of red mud into mesoporous Fe-aluminosilicate produced selective catalysts for the deoxygenation of waste cooking oil to green diesel hydrocarbons. Direct conversion of red mud in the presence cetyltrimethylammonium bromide into Fe-aluminosilicate (RM-CTA) produced a highly mesoporous structure with oligomeric Fe2O3 clusters within the pores. When red mud was treated with citric acid (RM-CA-CTA), a wide distribution of Fe2O3 particles was obtained on the aluminosilicate external surface. TEM analysis showed a well-defined hexagonal mesoporosity of Fe-aluminosilicate obtained from untreated red mud, while the treated red mud produced lower regularity mesopores. RM-CTA exhibits 60% WCO conversion and 83.72% selectivity towards liquid products with 80.44% diesel hydrocarbon (C11-C18) yield. The high selectivity was due to the high acidity of Fe-aluminosilicate to dissociate the C-O bond and the regularity of mesostructure for efficient hydrocarbon diffusion, preventing a cracking reaction.

Electrochemical Reduction and Oxidation of Chlorinated Aromatic Compounds Enhanced by the Fe-ZSM-5 Catalyst: Kinetics and Mechanisms

Devising cost-effective electrochemical catalyst system for the efficient degradation of chlorinated aromatic compounds is urgently needed for environmental pollution control. Herein, a Fe-ZSM-5 zeolite was used as a suspended catalyst to facilitate the degradation of lindane as a model chlorinated pesticide in an electrochemical system consisting of the commercial DSA (Ti/RuO₂-IrO₂) anode and graphite cathode. It was found that the Fe-ZSM-5 zeolite greatly accelerated the degradation of lindane, with the degradation rate constant more than 8 times higher than that without Fe-ZSM-5. In addition, the Fe-ZSM-5 zeolite widened the working pH range from 3 to 11, while efficient degradation of lindane in the absence of Fe-ZSM-5 was only obtained at pH ≤ 5. The degradation of lindane was primarily due to reductive dechlorination mediated by atomic H* followed by ^•OH oxidation. Fe-ZSM-5 zeolite could enrich lindane, H*, and ^•OH on its surface, thus provided a suitable local environment for lindane degradation. The Fe-ZSM-5 zeolite exhibited high stability and reusability, and reduced the energy consumption. This research provides a potential reduction-oxidation strategy for removing organochlorine compounds through a cost-efficient Fe-ZSM-5 catalytic electrochemical system.

Metal Sites in Zeolites: Synthesis, Characterization, and Catalysis

Zeolites with ordered microporous systems, distinct framework topologies, good spatial nanoconfinement effects, and superior (hydro)thermal stability are an ideal scaffold for planting diverse active metal species, including single sites, clusters, and nanoparticles in the framework and framework-associated sites and extra-framework positions, thus affording the metal-in-zeolite catalysts outstanding activity, unique shape selectivity, and enhanced stability and recyclability in the processes of Brønsted acid-, Lewis acid-, and extra-framework metal-catalyzed reactions. Especially, thanks to the advances in zeolite synthesis and characterization techniques in recent years, zeolite-confined extra-framework metal catalysts (denoted as metal@zeolite composites) have experienced rapid development in heterogeneous catalysis, owing to the combination of the merits of both active metal sites and zeolite intrinsic properties. In this review, we will present the recent developments of synthesis strategies for incorporating and tailoring of active metal sites in zeolites and advanced characterization techniques for identification of the location, distribution, and coordination environment of metal species in zeolites. Furthermore, the catalytic applications of metal-in-zeolite catalysts are demonstrated, with an emphasis on the metal@zeolite composites in hydrogenation, dehydrogenation, and oxidation reactions. Finally, we point out the current challenges and future perspectives on precise synthesis, atomic level identification, and practical application of the metal-in-zeolite catalyst system.

Hydrogen Production from Coal Industry Methane

Coal industry methane is a fossil raw material that can serve as an energy carrier for the production of heat and electricity, as well as a raw material for obtaining valuable products for the chemical industry. To ensure the safety of coal mining, rational environmental management and curbing global warming, it is important to develop and improve methods for capturing and utilizing methane from the coal industry. This review looks at the scientific basis and promising technologies for hydrogen production from coal industry methane and coal production. Technologies for catalytic conversion of all types of coal industry methane (Ventilation Air Methane – VAM, Coal Mine Methane – CMM, Abandoned Mine Methane – AMM, Coal-Bed Methane – CBM), differing in methane concentration and methane-to-air ratio, are discussed. The results of studies on the creation of a number of efficient catalysts for hydrogen production are presented. The great potential of hybrid methods of processing natural coal and coal industry methane has been demonstrated.

Enhancing metal dispersion over an Mo/ZSM-5 catalyst for methane dehydroaromatization

Mo dispersion is the key factor promoting the performance of an Mo/ZSM-5 catalyst for the methane dehydroaromatization (MDA) reaction.