Controlled Synthesis And Catalytic Application Of Cu-Co Mixed Oxides

Volatile organic compounds (VOCs) are one of the main air pollutants. In humans gathered metropolitan areas, VOCs which mainly originated from the combustion of fossil fuels are harmful to human health and will cause environmental effects, such as smog. Many countries have imposed relevant acts to reduce VOCs emissions. Catalytic combustion is one of the most effective and economical technologies to reduce VOCs emissions. Compared to traditional noble metal catalysts, transition metal oxides (TMO), such as copper, cobalt, chromium and manganese oxides have the merits of low cost and a comparable catalytic activity to those noble metals. With low cost transition metal oxides catalysts, catalytic combustion is promising to have a widespread apllication in the abatement of VOCs.In this work, cobalt oxides and copper-cobalt bimetallic oxides were successfully synthesized on an inert carrier by pulsed-spray evaporation chemical vapor deposition (PSE-CVD), the obtained oxides were applied to the abatement of VOCs. The structure, morphology and surface composition of the prepared films was investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The lattice stability limit was determined by a newly designed in situ Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS). In situ DRIFTS was also employed in the analysis of surface catalytic reactions. The effects of substrate temperature and mixing Cu/Co ratios were analyzed. As model molecules, the total oxidation of CO and C3H6 were used to test the catalytic performance of the deposited oxides.For obtained cobalt oxides:the structural analysis indicated that those thin films transformed from CoO to pure CO3O4 spinel as the temperature rose from 350 to 450℃. A homogeneous grain distribution was observed, oxygen was mainly composed of lattice oxygen and adsorbed oxygen constituted a minor proportion. The catalytic tests of propene showed that all the thin films exhibited prominent catalytic performances. According to the observed adsorption peaks of propene at low-temperature and transformation of CoO-Co3O4 from the in situ DRIFTS spectra, a combined redox and L-H mechanism was proposed for the catalytic oxidation of propene over cobalt oxide films. The porous structure and adsorbed oxygen on the film surface may well contribute to the catalytic oxidation of propene.For mixed copper-cobalt oxides, The results showed the progressive incorporation of cobalt in copper oxide and the formation of CuO/CoO mixture or mixed oxides with uniform sphere-like morphologies. Besides introducing more adsorbed oxygen, the cobalt addition tends to improve the upper stability limit of the Cu-Co oxides. The obtained Cu-Co binary oxides exhibit excellent performance for the total oxidation of CO and C3H6. A cooperative effect of the catalytic performance and the thermal stability as a consequence of the cobalt incorporation in the matrix of CuO has been revealed. The catalysts containing low cobalt content were substantially more active but less stable than the binary Cu-Co catalysts with higher Co content in the oxide phase. As cobalt content increases, the second oxide phase CoO was formed as consequence of the saturation of the CuO lattice with Co2+ species, which will induce properties changes, such as structure, morphology, thermal stability and catalytic activity.