Morphology effect on the structure-activity relationship of Rh/CeO2-ZrO2 catalysts

Abstract

Four CeO2–ZrO2 mixed oxides with different morphologies were synthesized using hydrothermal (polyhedra, rods and plates) and coprecipitation method (disordered). Detail structural/physio-chemical characterizations, catalytic activity measurements as well as in situ DRIFTS were conducted on the obtained ceria-zirconia as well as its supported Rh-only TWCs. The CeO2-ZrO2 mixed oxides present different exposed crystal planes and the catalytic performance of Rh/CeO2-ZrO2 is closely related to such different microstructures. Polyhedra shaped CeO2-ZrO2 exhibits increased lattice micro-strain originated from lattice distortion and defects, which can promote the mobility of bulk oxygen species to the surface, resulting in better three-way performance. Disordered Rh/CeO2-ZrO2 catalyst with high surface area and OSC shows wider static operation window, but the surface rhodium species tend to exist as Rh4+ with low redox ability which not favorable for the redox reactions. Besides, the lack of intermediate Rh-(NO)2 and Rh-CN species over disordered Rh/CeO2-ZrO2 based on in situ DRIFTS further reveals its unsatisfactory performance for NOx conversion.