Bimetallic catalysts for the catalytic combustion of methane using microreactor technology

Recent Advances in the Catalytic Conversion of Methane to Methanol: From the Challenges of Traditional Catalysts to the Use of Nanomaterials and Metal-Organic Frameworks

Methane and carbon dioxide are the main contributors to global warming, with the methane effect being 25 times more powerful than carbon dioxide. Although the sources of methane are diverse, it is a very volatile and explosive gas. One way to store the energy content of methane is through its conversion to methanol. Methanol is a liquid under ambient conditions, easy to transport, and, apart from its use as an energy source, it is a chemical platform that can serve as a starting material for the production of various higher-value products. Accordingly, the transformation of methane to methanol has been extensively studied in the literature, using traditional catalysts as different types of zeolites. However, in the last few years, a new generation of catalysts has emerged to carry out this transformation with higher conversion and selectivity, and more importantly, under mild temperature and pressure conditions. These new catalysts typically involve the use of a highly porous supporting material such as zeolite, or more recently, metal-organic frameworks (MOFs) and graphene, and metallic nanoparticles or a combination of different types of nanoparticles that are the core of the catalytic process. In this review, recent advances in the porous supports for nanoparticles used for methane oxidation to methanol under mild conditions are discussed.

Catalysis by platinum and palladium species confined in the bulk of glass fibre materials

The results of studies on the application of silicate glass fibre materials in catalysis are summarized and analyzed. Despite the very low noble metal content, catalysts based on these materials showed exceptionally high activities and selectivities in some catalytic reactions. This is due to specificity of the glassy state, which makes it possible, first, to confine highly dispersed palladium and platinum species in the bulk of glass fibres and, second, selectively absorb polar molecules, thus excluding the undesirable reactions involving non-polar molecules. The size dependences of the complete oxidation of propane and selective hydrogenation of acetylene, the nature of the structure sensitivity of these reactions and the reaction mechanisms are discussed. Ways for improving glass fibre catalyst performance are proposed and examples of the successful application of Pt/glass fibre catalysts for purification of industrial gases from volatile organic compounds are given.

The bibliography includes 175 references.

CO Total and Preferential Oxidation over Stable Au/TiO2 Catalysts Derived from Preformed Au Nanoparticles

CO preferential oxidation (PROX) is an effective method to clean reformate H2 streams to feed low-temperature fuel cells. In this work, the PROX and CO oxidation reactions were studied on preformed Au nanoparticles (NPs) supported on TiO2 anatase. Preformed Au NPs were obtained from gold cores stabilized by dodecanethiols or trimethylsilane-dendrons. A well-controlled size of ca. 2.6 nm and narrow size distributions were achieved by this procedure. The catalysts were characterized by high-resolution transmission electron microscopy and ex situ and in situ X-ray photoelectron spectroscopy (XPS). The XPS results showed that the preformed Au NPs exhibited high thermal stability. The different ligand-derived Au catalysts, as well as a conventional gold catalyst for comparison purposes, were loaded onto cordierite supports with 400 cells per square inch. The activity and selectivity of the samples were evaluated for various operation conditions. The catalyst prepared using dodecanethiol-capped Au NPs showed the best performance. In fact, CO conversions of up to 70% at 40% CO2 selectivity and 90% O2 conversion were observed operating at 363 K in H2-rich atmospheres. The performance of the best catalysts was subsequently tested on stainless steel microreactors. A 500-hour stability test was carried out under a real post-reformate stream, including 18 vol.% CO2 and 29 vol.% H2O. A mean CO conversion of ca. 24% was measured for the whole test operating at 453 K and a gas hourly space velocity (GHSV) of 1.3 × 104 h−1. These results reveal our dodecanethiol- and carbosilane-derived Au catalysts as extremely promising candidates to conduct a PROX reaction while avoiding deactivation, which is one of the major drawbacks of Au/TiO2 catalysts.

Transition metal pairs on ceria-promoted, ordered mesoporous alumina as catalysts for the CO2 reforming reaction of methane

Cobalt and iron clusters dispersed over ordered mesoporous γ-Al₂O₃ enable stable conversion of methane and carbon dioxide to syngas. Tungsten containing catalysts deactivate with TOS. Ceria–zirconia redox promotion is crucial for preventing carbon accumulation.

Total oxidation of propane on Pt/WOx/Al2O3 catalysts by formation of metastable Ptδ+ species interacted with WOx clusters

A series of Pt/Al(2)O(3) catalysts with various tungsten oxide loadings were prepared by a stepwise wet impregnation method. The catalysts were characterized by X-ray diffraction, nitrogen physisorption, Raman, UV-vis diffuse reflectance, transmission electron microscopy and infrared spectroscopy of adsorbed probe molecules (CO, NH(3) or C(3)H(8)). The propane oxidation activity of Pt/Al(2)O(3) catalyst is significantly improved by the addition of tungsten oxide. The tungsten oxide overlayer is presented as monomeric/polymeric WO(x) clusters and WO(3) crystals depending on the loading amount. The most active catalyst occurs at an intermediate surface tungsten density corresponding to the maximum of polytungstate species. The electronic interactions between Pt and WO(x) clusters lead to the generation of more reducible Pt(δ+) species which are suggested to be active sites for propane oxidation. Basically, a simple model is proposed involving the initial CH bond activation at the platinum-tungsten oxide interface.