Silver nanoparticles supported on zirconia-ceria for the catalytic wet air oxidation of methyl tert-butyl ether

Abstract

In this work Ag nanoparticles supported on ZrO2-CeO2 promoted with different amounts of CeO2 (0, 0.5, 1, 5, 10, 15 and 20 wt%) were synthesized by deposition-precipitation method in order to test the Catalytic Wet Air Oxidation (CWAO) of Methyl Tert-Butyl Ether (MTBE). X-ray diffraction patterns reveal that the tetragonal ZrO2 phase (t-ZrO2) present in the catalysts is stabilized by the presence of CeO2, forming a solid solution, and preventing transformation to the monoclinic phase (m-ZrO2). The t-ZrO2 stability and the dispersion of Ag on ZrO2 increase with CeO2 concentration. HRTEM images confirmed that the mean crystallite size of supports and monometallic Ag catalyst decreases by CeO2 addition. CeO2 can also improve the reduction of Ag2O and increase also the d-electron density of the surface silver atoms. Furthermore, CeO2 has a promoting effect on silver supported zirconia-ceria because of the strong metal-support interaction and its relationship of oxygen vacancies of zirconia-ceria support. The extent of reduction of silver controls the quantity of oxygen to be adsorbed during the catalytic oxidation reaction. In general, a small crystal size and high metallic dispersion can enhance the activity of MTBE catalytic wet air oxidation. The Ag/ZrO2-(15%)CeO2 catalyst was the most active with 90% MTBE conversion.