The Effect of Rh on the Interaction of Co with Al2O3 and CeO2 Supports

Catalytic combustion of lean methane over different Co3O4 nanoparticle catalysts

Three types of Co3O4 catalyst, namely Co3O4 nanoparticles (denoted as Co3O4-NPs, ∼12 nm in diameter), Co3O4 nanoparticles encapsulated in mesoporou s SiO2 (denoted as Co3O4@SiO2), and Co3O4 nanoparticles inside microporous SiO2 hollow sub-microspheres (denoted as Co3O4-in-SiO2), were explored to catalyze the combustion of lean methane. It was found that the methane conversion over the three catalysts has the order of Co3O4-NPs ≈ Co3O4@SiO2 > Co3O4-in-SiO2 due to the different catalyst structure. The comparison experiments at high temperatures indicate the Co3O4@SiO2 has a significantly improved anti-sintering performance. Combined with the TEM and BET measurements, the results prove that the presence of the mesoporous SiO2 layer can maintain the catalytical activity and significantly improve the anti-sintering performance of Co3O4@SiO2. In contrast, the microporous SiO2 layer reduces the catalytical activity of Co3O4-in-SiO2 possibly due to its less effective diffusion path of combustion product. Thus, the paper demonstrates the pore size of SiO2 layer and catalyst structure are both crucial for the catalytical activity and stability.

Comparative Study of the Efficiency of Different Noble Metals Supported on Hydroxyapatite in the Catalytic Lean Methane Oxidation under Realistic Conditions

The combustion of lean methane was studied over palladium, rhodium, platinum, and ruthenium catalysts supported on hydroxyapatite (HAP). The samples were prepared by wetness impregnation and thoroughly characterized by BET, XRD, UV-Vis-NIR spectroscopy, H₂-TPR, OSC, CO chemisorption, and TEM techniques. It was found that the Pd/HAP and Rh/HAP catalysts exhibited a higher activity compared with Pt/HAP and Ru/HAP samples. Thus, the degree of oxidation of the supported metal under the reaction mixture notably influenced its catalytic performance. Although Pd and Rh catalysts could be easily re-oxidized, the re-oxidation of Pt and Ru samples appeared to be a slow process, resulting in small amounts of metal oxide active sites. Feeding water and CO₂ was found to have a negative effect, which was more pronounced in the presence of water, on the activity of Pd and Rh catalysts. However, the inhibiting effect of CO₂ and H₂O decreased by increasing the reaction temperature.

Effectively Regulating the Microenvironment of Atomically Dispersed Rh through Co and Pi to Promote the Selectivity in Olefin Hydroformylation

In the study of heterogeneity of homogeneous processes, effective control of the microenvironment of active sites is a reliable means to improve the selectivity of products. Here, we develop a high-performance Rh-based atomically dispersed catalyst for olefin hydroformylation by controlling the electronic environment and spatial distribution of active metals on the supports, which is achieved through wet impregnation of Rh on ZnO modified with Pi and Co. Various characterizations demonstrate that Co weakens Rh-CO interactions and Pi promotes the formation of atomically dispersed Rh, which thereby improves the selectivity of linear aldehydes in hydroformylation. This strategy of rationally designing the local microenvironment of active metals is important to optimize the catalytic performance.

Effects of the addition of CeO2 on the steam reforming of ethanol using novel carbon-Al2O3 and carbon-ZrO2 composite-supported Co catalysts

Novel carbon-Al₂O₃ and carbon-ZrO₂ composite-supported Co catalysts were prepared using the sol–gel method with polyethylene glycol (PEG) as a carbon source, and the effects of the addition of CeO₂ to catalysts on the steam reforming of ethanol were investigated. The reactions were carried out in a fixed bed reactor with H₂O/EtOH = 12 (mol/mol) and a temperature range of 300 °C to 600 °C. The catalyst characterization was performed by XRD, nitrogen adsorption and desorption isotherms, TG-DTA, XRF and TEM. Although the carbon-Al₂O₃ composite-supported Co catalysts exhibited a higher conversion of ethanol than the carbon-ZrO₂ composite-supported Co catalysts, the effect of the addition of CeO₂ was hardly observed for catalysts with Al₂O₃. In contrast to the case of catalysts with Al₂O₃, the effect of the addition of CeO₂ to catalysts with ZrO₂ on the conversion and the hydrogen yield was observed, and the hydrogen yield at 600 °C exceeded that of catalysts with Al₂O₃. 16Co42C31.5Ce10.5Zr exhibited the highest hydrogen yield of 89% at 600 °C. Fine Co metal species were observed for the used ZrO₂-based catalysts, while Co₃O₄ peaks were observed for the used Al₂O₃-based catalysts. The development of the carbon nanotube-like structure with a diameter of 50 nm was observed with particles having diameters of 30 nm to 50 nm, suggesting that the carbon deposition might occur so as not to deactivate the catalyst.

For the ideal reaction routes in steam reforming of ethanol catalyzed by Co/CeO₂–ZrO₂, as Al₂O₃ was used instead of ZrO₂, the effect of CeO₂ did not appear, suggesting that the configuration of CeO₂ and cobalt species on ZrO₂ would be important.

The structure and catalytic properties of Rh-doped CeO2 catalysts

The PDF analysis with TEM, XPS and Raman spectroscopy indicates the formation of homogenous Rh_xCe_1−xO_2−δ nanocrystalline solid solutions.