In Situ Spectroscopic and Computational Studies on a MnO2-CuO Catalyst for Use in Volatile Organic Compound Decomposition.

In situ near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and density functional theory calculations were conducted to demonstrate the decomposition mechanism of propylene glycol methyl ether acetate (PGMEA) on a MnO2-CuO catalyst. The catalytic activity of MnO2-CuO was higher than that of MnO2 at low temperatures, although the pore properties of MnO2 were similar to those of MnO2-CuO. In addition, whereas the chemical state of MnO2 remained constant following PGMEA dosing at 150 °C, MnO2-CuO was reduced under identical conditions, as confirmed by in situ NEXAFS spectroscopy. These results indicate that the presence of Cu in the MnO2-CuO catalyst enables the release of oxygen at lower temperatures. More specifically, the released oxygen originated from the Mn-O-Cu moiety on the top layer of the MnO2-CuO structure, as confirmed by calculation of the oxygen release energies in various oxygen positions of MnO2-CuO. Furthermore, the spectral changes in the in situ NEXAFS spectrum of MnO2-CuO following the catalytic reaction at 150 °C corresponded well with those of the simulated NEXAFS spectrum following oxygen release from Mn-O-Cu. Finally, after the completion of the catalytic reaction, the quantities of lactone and ether functionalities in PGMEA decreased, whereas the formation of C=C bonds was observed.

NiO/CeO2-ZnO nano-catalysts for direct synthesis of dimethyl carbonate from methanol and carbon dioxide.

XNiO/CeO2(0.7)-ZnO(0.3) (X = 0, 1, 5, 10, and 15) nano-catalysts were prepared by a wet impregnation method with a variation of NiO content (X, wt%). The prepared catalysts were then applied to the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Successful formation of XNiO/CeO2(0.7)-ZnO(0.3) nano-catalysts was confirmed by XRD and ICP-AES analyses. Acidity and basicity of XNiO/CeO2-ZnO were measured by NH3-TPD (temperature-programmed desorption) and CO2-TPD experiments, respectively, with an aim of elucidating the effect of acidity and basicity of the catalysts on the catalytic performance in the reaction. It was revealed that the catalytic activity of XNiO/CeO2(0.7)-ZnO(0.3) was closely related to both acidity and basicity of the catalysts. The amount of dimethyl carbonate produced over XNiO/CeO2(0.7)-ZnO(0.3) increased with increasing acidity and basicity of the catalysts. Thus, both acidity and basicity of the catalysts played important roles in determining the catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide.

Direct synthesis of dimethyl carbonate from methanol and carbon dioxide over CeO2(X)-ZnO(1-X) nano-catalysts.

CeO2(X)-ZnO(1-X) (X = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) nano-catalysts were prepared by a co-precipitation method with a variation of CeO2 content (X, mol%), and they were applied to the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Successful formation of CeO2(X)-ZnO(1-X) nano-catalysts was well confirmed by XRD analysis. The amount of DMC produced over CeO2(X)-ZnO(1-X) catalysts exhibited a volcano-shaped curve with respect to CeO2 content. Acidity and basicity of CeO2(X)-ZnO(1-X) nano-catalysts were measured by NH3-TPD and CO2-TPD experiments, respectively, to elucidate the effect of acidity and basicity on the catalytic performance in the reaction. It was revealed that the catalytic performance of CeO2(X)-ZnO(1-X) nano-catalysts was closely related to the acidity and basicity of the catalysts. Amount of dimethyl carbonate increased with increasing both acidity and basicity of the catalysts. Among the catalysts tested, CeO2(0.7)-ZnO(0.3) with the largest acidity and basicity showed the best catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide.