No abstract

Co3O4 catalysts with three specific morphologies (nanocubes, nanosheets, and nanooctahedra) were prepared using simple preparation methods and tested for catalytic combustion of propane under the same reaction conditions.

The catalytic performance of MnO 2 (x)−CeO 2 (x = Mn/Ce molar ratio) and the synergistic effect have been investigated in formaldehyde removal. The results showed that formaldehyde achieved 100% conversion at 60 °C for MnO 2 (1.5)−CeO 2 , with the gas hourly space velocity = 120 000 mL h −1 g cat −1. It was lower than the formaldehyde removal temperature of MnO 2 (130 °C) and CeO 2 (170 °C). The apparent activation energy for HCHO oxidation with MnO 2 (1.5)−CeO 2 was 34.2 kJ mol −1 . The partial mutual replacement of Mn x+ and Ce x+ decreases the crystallite size due to the MnO 2 / CeO 2 interaction. The X-ray photoelectron spectroscopy and the Raman analyses show that the Mn 3+ /Mn and O ads /O latt ratios and the relative concentrations of oxygen vacancies for MnO 2 (1)−CeO 2 and MnO 2 (1.5)− CeO 2 were higher than those of the rest of the catalysts. Thus, the lattice oxygen (O latt ) from CeO 2 readily transfers to the oxygen vacancy, achieving O latt activation to surface-adsorbed oxygen (O ads ).

Cobalt–nickel mixed oxides with different Co/Ni molar ratios were prepared by co‐precipitation and used for the catalytic combustion of lean methane. The catalytic performances for methane combustion were evaluated at steady‐state conditions at temperatures ranging from 250 to 500 °C, which were increased in step sizes of 25 °C. Among the catalysts, the cobalt–nickel mixed‐oxide catalysts with an appropriate Co/Ni ratio exhibit a high catalytic performance for the lean methane combustion, with the catalyst having a Co/Ni molar ratio of 1:4 showing the highest catalytic activity (methane conversion reached 100 % at 425 °C). On the basis of TEM and XRD results, the nanoparticles of the catalysts have a suitable interparticle spacing and more crystal defects. X‐ray photoelectron spectroscopy (XPS) results reveal a high number of surface‐active oxygen species and appropriate aliovalent cobalt ion numbers in the catalysts for high catalytic activity. All these effects contribute to the outstanding performance of these catalysts in the combustion of lean methane at low temperatures.

A series of Pd‐based core–shell catalysts (Pd@SiO2, Pd@CeO2, and Pd@ZrO2) supported on Si‐modified Al2O3 were prepared for the catalytic combustion of lean methane. Pd@SiO2 exhibited slightly lower catalytic activity than Pd@CeO2 and higher catalytic activity than Pd@ZrO2 in dry conditions; however, Pd@SiO2 had the highest catalytic activity among the three catalysts in the presence of high concentrations of water vapor. Furthermore, the Pd@SiO2 catalyst showed good thermal stability and resistivity to water poisoning. CO chemisorption and TEM results demonstrated that the core–shell structure could help in the stabilization of the active phase compared to the uncoated Pd/Si‐Al2O3 catalyst. XRD and X‐ray photoelectron spectroscopy results indicated that a balanced mixed phase of PdOx/Pd0 is the main active phase of these Pd‐based catalysts.