Non-Oxidative Propane Dehydrogenation on CrOx-ZrO2-SiO2 Catalyst Prepared by One-Pot Template-Assisted Method.

A series of CrOx-ZrO2-SiO2 (CrZrSi) catalysts was prepared by a "one-pot" template-assisted evaporation-induced self-assembly process. The chromium content varied from 4 to 9 wt.% assuming Cr2O3 stoichiometry. The catalysts were characterized by XRD, SEM-EDX, temperature-programmed reduction (TPR-H2), Raman spectroscopy, and X-ray photoelectron spectroscopy. The catalysts were tested in non-oxidative propane dehydrogenation at 500-600 °C. The evolution of active sites under the reaction conditions was investigated by reductive treatment of the catalysts with H2. The catalyst with the lowest Cr loading initially contained amorphous Cr3+ and dispersed Cr6+ species. The latter reduced under reaction conditions forming Cr3+ oxide species with low activity in propane dehydrogenation. The catalysts with higher Cr loadings initially contained highly dispersed Cr3+ species stable under the reaction conditions and responsible for high catalyst activity. Silica acted both as a textural promoter that increased the specific surface area of the catalysts and as a stabilizer that inhibited crystallization of Cr2O3 and ZrO2 and provided the formation of coordinatively unsaturated Zr4+ centers. The optimal combination of Cr3+ species and coordinatively unsaturated Zr4+ centers was achieved in the catalyst with the highest Cr loading. This catalyst showed the highest efficiency.

Template Synthesis of Porous Ceria-Based Catalysts for Environmental Application.

Porous oxide materials are widely used in environmental catalysis owing to their outstanding properties such as high specific surface area, enhanced mass transport and diffusion, and accessibility of active sites. Oxides of metals with variable oxidation state such as ceria and double oxides based on ceria also provide high oxygen storage capacity which is important in a huge number of oxidation processes. The outstanding progress in the development of hierarchically organized porous oxide catalysts relates to the use of template synthetic methods. Single and mixed oxides with enhanced porous structure can serve both as supports for the catalysts of different nature and active components for catalytic oxidation of volatile organic compounds, soot particles and other environmentally dangerous components of exhaust gases, in hydrocarbons reforming, water gas shift reaction and photocatalytic transformations. This review highlights the recent progress in synthetic strategies using different types of templates (artificial and biological, hard and soft), including combined ones, in the preparation of single and mixed oxide catalysts based on ceria, and provides examples of their application in the main areas of environmental catalysis.

Hydrodechlorination of 4-Chlorophenol on Pd-Fe Catalysts on Mesoporous ZrO2SiO2 Support.

A mesoporous support based on silica and zirconia (ZS) was used to prepare monometallic 1 wt% Pd/ZS, 10 wt% Fe/ZS, and bimetallic FePd/ZS catalysts. The catalysts were characterized by TPR-H2, XRD, SEM-EDS, TEM, AAS, and DRIFT spectroscopy of adsorbed CO after H2 reduction in situ and tested in hydrodechlorination of environmental pollutant 4-chlorophelol in aqueous solution at 30 °C. The bimetallic catalyst demonstrated an excellent activity, selectivity to phenol and stability in 10 consecutive runs. FePd/ZS has exceptional reducibility due to the high dispersion of palladium and strong interaction between FeOx and palladium, confirmed by TPR-H2, DRIFT spectroscopy, XRD, and TEM. Its reduction occurs during short-time treatment with hydrogen in an aqueous solution at RT. The Pd/ZS was more resistant to reduction but can be activated by aqueous phenol solution and H2. The study by DRIFT spectroscopy of CO adsorbed on Pd/ZS reduced in harsh (H2, 330 °C), medium (H2, 200 °C) and mild conditions (H2 + aqueous solution of phenol) helped to identify the reasons of the reducing action of phenol solution. It was found that phenol provided fast transformation of Pd+ to Pd0. Pd/ZS also can serve as an active and stable catalyst for 4-PhCl transformation to phenol after proper reduction.

Hydrogen dissociation catalyzed by carbon-coated nickel nanoparticles: experiment and theory.

Based on the combination of experimental measurements and first-principles calculations we report a novel carbon-based catalytic material and describe significant acceleration of the hydrogenation of magnesium at room temperature in the presence of nickel nanoparticles wrapped in multilayer graphene. The increase in rate of magnesium hydrogenation in contrast to a mix of graphite and nickel nanoparticles evidences intrinsic catalytic properties of the nanocomposites explored. The results from simulation demonstrate that doping of the metal substrate and the presence of Stone-Wales defects turn multilayer graphene from being chemically inert to chemically active. The role of the size of the nanoparticles and temperature are also discussed.