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.