Recent Advances of Indium Oxide-Based Catalysts for CO2 Hydrogenation to Methanol: Experimental and Theoretical.

Methanol synthesis from the hydrogenation of carbon dioxide (CO2) with green H2 has been proven as a promising method for CO2 utilization. Among the various catalysts, indium oxide (In2O3)-based catalysts received tremendous research interest due to the excellent methanol selectivity with appreciable CO2 conversion. Herein, the recent experimental and theoretical studies on In2O3-based catalysts for thermochemical CO2 hydrogenation to methanol were systematically reviewed. It can be found that a variety of steps, such as the synthesis method and pretreatment conditions, were taken to promote the formation of oxygen vacancies on the In2O3 surface, which can inhibit side reactions to ensure the highly selective conversion of CO2 into methanol. The catalytic mechanism involving the formate pathway or carboxyl pathway over In2O3 was comprehensively explored by kinetic studies, in situ and ex situ characterizations, and density functional theory calculations, mostly demonstrating that the formate pathway was extremely significant for methanol production. Additionally, based on the cognition of the In2O3 active site and the reaction path of CO2 hydrogenation over In2O3, strategies were adopted to improve the catalytic performance, including (i) metal doping to enhance the adsorption and dissociation of hydrogen, improve the ability of hydrogen spillover, and form a special metal-In2O3 interface, and (ii) hybrid with other metal oxides to improve the dispersion of In2O3, enhance CO2 adsorption capacity, and stabilize the key intermediates. Lastly, some suggestions in future research were proposed to enhance the catalytic activity of In2O3-based catalysts for methanol production. The present review is helpful for researchers to have an explicit version of the research status of In2O3-based catalysts for CO2 hydrogenation to methanol and the design direction of next-generation catalysts.

Fabrication of supported Pt/CeO2 nanocatalysts doped with different elements for CO oxidation: theoretical and experimental studies.

Supported Pt/CeO2 catalysts have been widely used in carbon monoxide (CO) oxidation; however, the high oxygen vacancy formation energy (Evac) in the process leads to the poor performance of these catalysts. Herein, we explored different element (Pr, Cu, or N) doped CeO2 supports using Ce-based metal-organic frameworks (MOFs) as precursors via calcination treatment. The obtained CeO2 supports were used to load Pt nanoparticles. These catalysts were systematically characterized by various techniques, and they showed superior catalytic activity for CO oxidation compared to undoped catalysts which could be attributed to the formation of Ce3+, and high amounts of Oads/(Oads + Olat) and Ptδ+/Pttotal. Moreover, density functional theory calculations with on-site Coulomb interaction correction (DFT+U) were performed to provide atomic-scale insights into the reaction process by the Mars-van Krevelen (M-vK) mechanism, which revealed that the element-doped catalysts could simultaneously reduce the adsorption energies of CO and lower reaction energy barriers in the *OOCO associative pathway.

Cobalt Phthalocyanine Supported on Mesoporous CeO2 as an Active Molecular Catalyst for CO Oxidation.

Heterogenization of biomolecules by immobilizing on a metal oxide support could greatly enhance their catalytic activity and stability, but their interactions are generally weak. Herein, cobalt phthalocyanine (CoPc) molecules were firmly anchored on a Ce-based metal-organic framework (Ce-BTC) due to π-π stacking interaction between CoPc and aromatic frameworks of the BTC linker, which was followed by a calcination treatment to convert Ce-BTC to mesoporous CeO2 and realize a molecular-level dispersion of CoPc on the surface of CeO2. Various characterization results confirm the successful fabrication of molecular-based CoPc/CeO2 catalysts which exhibited good CO oxidation performance. Importantly, we found that the mixing manner of Ce-BTC and CoPc remarkably affects the physicochemical properties which then determined the catalytic performance of the resultant CoPc/CeO2 catalysts. In contrast, the direct physical mixing of CoPc and CeO2 led to poor performance toward CO oxidation, manifesting that the Ce-BTC-mediated CoPc loading strategy is promising for the heterogenization of catalytic biomolecules.

Metal oxide/CeO2 nanocomposites derived from Ce-benzene tricarboxylate (Ce-BTC) adsorbing with metal acetylacetonate complexes for catalytic oxidation of carbon monoxide.

Herein, a series of metal oxide/CeO2 (M/CeO2) nanocomposites derived from Ce-benzene tricarboxylate (Ce-BTC) adsorbing with different metal acetylacetonate complexes were prepared for CO oxidation under four different CO gas atmospheres. It was demonstrated that Cu/CeO2 exhibited the highest catalytic activity and stability in CO oxidation. Remarkably, both O2 selectivity and CO selectivity to CO2 are 100% in most of the investigated conditions. Several analytical tools such as N2 adsorption-desorption and powder X-ray diffraction, were employed to characterize the prepared catalysts. In addition, the excellent catalytic performance of Cu/CeO2 in CO oxidation was revealed by H2 temperature-program reduction experiment, X-ray photoelectron spectroscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The result showed that high oxygen vacancy and high CO adsorption capacity (Cu+-CO) caused by the electron exchanges of Cu2+/Cu+ and Ce3+/Ce4+ pairs (Ce4+ + Cu+ ⇆ Ce3+ + Cu2+) are two key factors contributing to the high oxidation performance of Cu/CeO2 catalyst.