An Overview of Recent Development in Composite Catalysts from Porous Materials for Various Reactions and Processes

Catalysts are important to the chemical industry and environmental remediation due to their effective conversion of one chemical into another. Among them, composite catalysts have attracted continuous attention during the past decades. Nowadays, composite catalysts are being used more and more to meet the practical catalytic performance requirements in the chemical industry of high activity, high selectivity and good stability. In this paper, we reviewed our recent work on development of composite catalysts, mainly focusing on the composite catalysts obtained from porous materials such as zeolites, mesoporous materials, carbon nanotubes (CNT), etc. Six types of porous composite catalysts are discussed, including amorphous oxide modified zeolite composite catalysts, zeolite composites prepared by co-crystallization or overgrowth, hierarchical porous catalysts, host-guest porous composites, inorganic and organic mesoporous composite catalysts, and polymer/CNT composite catalysts

Water-Involved Methane Selective Catalytic Oxidation by Dioxygen over Copper-Zeolites

The selective oxidation of methane to methanol is a dream reaction of direct methane functionalization, which remains a key challenge in catalysis and a hot issue of controversy. Herein, we report the water-involved methane selective catalytic oxidation by dioxygen over copper-zeolites. At 573 K, a state-of-the-art methanol space-time yield of 543 mmol/molCu/h with methanol selectivity of 91 % is achieved with Cu-CHA catalyst. Temperature-programmed surface reactions with isotope labelling determine water as the dominating oxygen and hydrogen source of hydroxyl in methanol while dioxygen participates in the reaction through reducing to water. Spectroscopic analyses reveal the fast redox cycle of Cu2+-Cu+-Cu2+ during methane selective oxidation, which is closely related to the high catalytic activity of Cu-CHA. Density functional theory calculations suggest that both CuOH monomer and dimer in Cu-CHA can catalyze the selective oxidation of methane to methanol with Cu-OOH as the key reaction intermediate, and meanwhile, various copper sites undergo interconversion under reaction conditions.</p

Acetylene-Selective Hydrogenation Catalyzed by Cationic Confined in Zeolite

The selective hydrogenation of alkynes to alkenes is an important type of organic transformation with large-scale industrial applications. This transformation requires efficient catalysts with precise selectivity control, and palladium-based metallic catalysts are currently employed. Here we show that four-coordinated cationic nickel(II) confined in zeolite can efficiently catalyze the selective hydrogenation of acetylene to ethylene, a key process for trace acetylene removal prior to the polymerization process. Under optimized conditions, 100% acetylene conversion and an ethylene selectivity up to 97% are simultaneously achieved. This catalyst system also exhibits good stability and recyclability for potential applications. Spectroscopy investigations and density functional theory calculations reveal the heterolytic dissociation of hydrogen molecules and the importance of hydride and protons in the selective hydrogenation of acetylene to ethylene. This work provides an efficient strategy toward active and selective zeolite catalysts by utilizing the local electrostatic field within the zeolite confined space for small-molecule activation and by linking heterogeneous and homogeneous catalysis

Hexadecylphosphate-Functionalized Iron Oxide Nanoparticles: Mild Oxidation of Benzyl C–H Bonds Exclusive to Carbonyls by Molecular Oxygen

We report here a specially designed catalytic system consisting of hexadecyl­phosphate-functionalized iron oxide nanoparticles in oil/water biphasic emulsion. The iron oxide nanoparticles act as catalytic centers and the surface-bonded hexadecyl­phosphates as peripheral units which tune the activity of iron oxide and the access of reactants to the catalytic centers. The catalytic system is highly effective to oxidize the benzyl C–H bonds in a series of compounds to carbonyls exclusively by molecular oxygen under mild conditions. The catalytic process, green and low cost, offers a novel concept to design highly effective catalysts with nanoparticles as active centers and surface-bonded organic phosphates as accelerants for oxidation reactions

Nanotubular Gamma Alumina with High-Energy External Surfaces: Synthesis and High Performance for Catalysis

Inorganic nanocrystals catalysts with a high proportion of high-energy surfaces can bring about high performance for catalysis and has been an important research topic in the past decades. Gamma alumina is one of the most important inorganic oxides used as solid acids or catalytic support for many more industrial catalysts. However, the preparation of gamma alumina mainly with high-energy external surfaces has never been reported because it has a complicated crystal structure. We demonstrate here in depth a new-type γ-alumina material from a systematic investigation, which is controllably synthesized as regular nanotubes with high-energy {111} facets as main external surfaces. The new-type material shows much better performance as acid catalyst or catalytic support for metals, as compared with common γ-alumina whose main exposed surface is stable {100} or {110} facets in irregular morphology. As an example, palladium loaded on the new-type γ-alumina is easily prepared in higher dispersion and unique electronic states upon the stronger interaction with the support, giving rise to better catalytic performance for semihydrogenation of alkynes, without any assistance of other metals. The systematic investigation should open opportunities of catalyst innovation for new chemical reactions