RESUMO
A series of La-Ce-MnOx catalysts derived from the precipitation of acetate salt and ammonium carbonate were calcined at different temperatures and applied for the catalytic oxidation of soot from diesel exhausts. The structure states of the as-prepared catalysts and catalytic behaviour for soot oxidation were studied by many characterization techniques such as XRD, XANES, N2 adsorption-desorption, TPR, O2-TPD, XPS and TGA. XANES results display most Mn species are Mn4+ when the samples are calcined at 500 and 600°C. However, for MCLa-700 and MCLa-800 catalysts, the predominance valence is 3+ ions. The MCLa-500 and MCLa-600 catalysts possess higher concentrations of surface active oxygen evidenced by H2-TPR and soot-TPR. Therefore, the combustion rate of soot over MCLa-600 catalyst is remarkably increased with the T10, T50 and T90 at 318°C, 360°C and 388°C under NOx atmosphere respectively.
RESUMO
Oxygen vacancy sites on a catalyst surface have been extensively studied and been proved to promote the adsorption and activation of carbon dioxide. We use Sn-doped ZrO2 to prepare a Zr/Sn catalyst rich in oxygen vacancies (OVs) by co-precipitation. The yield of dimethyl carbonate is 5 times that of ZrO2. Compared with the original ZrO2, Zr/Sn exhibits a higher specific surface area, number of acid-base sites and a lower band gap, which improves the conductivity of electrons and creates more surface. The number of reaction sites greatly enhances the adsorption and activation capacity of CO2 molecules on the catalyst surface. In situ infrared spectroscopy shows that CO2 adsorbs on oxygen vacancies to form monomethyl carbonate, and participates in the reaction as an intermediate species. This work provides new clues for the preparation of ZrO2-based catalysts rich in oxygen vacancies to directly catalyze the synthesis of dimethyl carbonate from methanol and CO2.
