Role of oxygen vacancy in cobalt doped ceria catalyst for styrene epoxidation using molecular oxygen

Carbon Dioxide Valorization into Methane Using Samarium Oxide-Supported Monometallic and Bimetallic Catalysts

Samarium oxide (Sm2O3) is a versatile surface for CO2 and H2 interaction and conversion. Samarium oxide-supported Ni, samarium oxide-supported Co-Ni, and samarium oxide-supported Ru-Ni catalysts were tested for CO2 methanation and were characterized by X-ray diffraction, nitrogen physisorption, infrared spectroscopy, H2-temperature programmed reduction, and X-ray photoelectron spectroscopy. Limited H2 dissociation and widely available surface carbonate and formate species over 20 wt.% Ni, dispersed over Sm2O3, resulted in ~98% CH4 selectivity. The low selectivity for CO could be due to the reforming reaction between CH4 (methanation product) and CO2. Co-impregnation of cobalt with nickel over Sm2O3 had high surface adsorbed oxygen and higher CO selectivity. On the other hand, co-impregnation of ruthenium and nickel over Sm2O3 led to more than one catalytic active site, carbonate species, lack of formate species, and 94% CH4 selectivity. It indicated the following route of CH4 synthesis over Ru-Ni/Sm2O3; carbonate → unstable formate → CO → CH4.

Selective Oxidation of Alcohols and Alkenes with Molecular Oxygen Catalyzed by Highly Dispersed Cobalt (II) Decorated 12-Tungstosilicic Acid-Modified Zirconia

Traditional procedures for oxidation processes suffer from a lack of selectivity, the use of organic solvents, the toxicity of the reagents, and waste production. As a cleaner alternative, highly dispersed Co over 12-tungstosilicicacid modified zirconia was synthesized and used for the selective oxidation of benzyl alcohol and styrene with molecular oxygen to carbonyl compounds under environmentally benign solvent-free conditions. The supremacy of the present catalyst lies in achieving excellent selectivity (>90%) for products with a very high turnover number. The catalytic activity of the recycled catalysts was also explored under optimized conditions to confirm sustainability. Further, the viability of the catalyst was studied via oxidation of various alcohols and alkenes under optimized conditions as well as superiority by comparison with the reported catalysts.

Promotional mechanism of enhanced denitration activity with Cu modification in a Ce/TiO2-ZrO2 catalyst for a low temperature NH3-SCR system

This study aims to investigate the enhanced low temperature denitration activity and promotional mechanism of a cerium-based catalyst through copper modification. In this paper, copper and cerium oxides were supported on TiO2-ZrO2 by an impregnation method, their catalytic activity tests of selective catalytic reduction (SCR) of NO with NH3 were carried out and their physicochemical properties were characterized. The CuCe/TiO2-ZrO2 catalyst shows obviously enhanced NH3-SCR activity at low temperature (<300 °C), which is associated with the well dispersed active ingredients and the synergistic effect between copper and cerium species (Cu2+ + Ce3+ ↔ Cu+ + Ce4+), and the increased ratios of surface chemisorbed oxygen and Cu+/Cu2+ lead to the enhanced low-temperature SCR activity. The denitration reaction mechanism over the CuCe/TiO2-ZrO2 catalyst was investigated by in situ DRIFTS and DFT studies. Results illustrate that the NH3 is inclined to adsorb on the Cu acidic sites (Lewis acid sites), and the NH2 and NH2NO species are the key intermediates in the low-temperature NH3-SCR process, which can explain the promotional effect of Cu modification on denitration activity of Ce/TiO2-ZrO2 at the molecular level. Finally, we have reasonably concluded a NH3-SCR catalytic cycle involving the Eley-Rideal mechanism and Langmuir-Hinshelwood mechanism, and the former mechanism dominates in the NH3-SCR reaction.

Formation of Catalytic Active Sites in Hydrothermally Obtained Binary Ceria-Iron Oxides: Composition and Preparation Effects

A series of mesoporous cerium-iron binary oxides was prepared by a hydrothermal technique using CTAB as a template. The influence of the Fe/Ce ratio and the variations in the preparation techniques such as the type of solvent and the precipitation agent, the approach of the template release, and the temperature of calcination on the phase composition, textural, structural, surface, and redox properties of the obtained materials was studied in details by XRD, nitrogen physisorption, TPR, FTIR, UV-vis, XPS, Raman, and Moessbauer spectroscopies. The materials were tested as catalysts in methanol decomposition and total oxidation of ethyl acetate. It was assumed that the binary materials represented a complex mixture of differently substituted ceria- and hematite-like phases. Critical assessment of their formation on the base of a common mechanism scheme was proposed. This scheme declares the key role of the formation of shared Ce-O-Fe structures by insertion of Fe³⁺ in the ceria lattice and further competitive compensation of the lattice charge balance by the existing in the system ions, which could be controlled by the Fe/Ce ratio and the hydrothermal synthesis procedure used. This mechanism provides proper understanding and regulation of the catalytic behavior of cerium-iron oxide composites in methanol decomposition with a potential for hydrogen production and total oxidation of ethyl acetate as a model of VOCs.