Facile synthesis of ceria–zirconia solid solutions with cubic–tetragonal interfaces and their enhanced catalytic performance in diesel soot oxidation

Abstract

The rational design of a catalyst interface is crucial for the improvement of catalytic performance. Here, a CeO2–ZrO2 solid solution catalyst with cubic–tetragonal interfaces, CeO2–ZrO2(C-T), was synthesized using a solvothermal method. The catalytic performance of the prepared CeO2–ZrO2(C-T) catalyst in soot oxidation was compared with that of the current commercial CeZrLaPrOx and CeO2–ZrO2 soot oxidation catalysts; meanwhile, the catalysts were characterized systematically. X-ray diffraction and Raman spectroscopy results imply that cubic and tetragonal structures coexist, and the amounts of these phases are approximately equal (C/T = 41/59) in the synthesized CeO2–ZrO2(C-T) catalyst. Transmission electron microscopy images clearly demonstrate the presence of many cubic–tetragonal interfaces in the CeO2–ZrO2(C-T) catalyst. The prepared CeO2–ZrO2(C-T) catalyst has markedly better catalytic activity for soot oxidation than the commercial CeO2–ZrO2-based catalysts. This result is influenced by the existence of cubic-tetragonal interfaces in CeO2-ZrO2(C-T). X-ray photoelectron spectroscopy and oxygen temperature-programmed desorption results further indicate that the cubic–tetragonal interfaces in the synthesized CeO2–ZrO2(C-T) catalyst promote the production of structural defects (oxygen vacancies) and the release of surface lattice oxygen in the CeO2–ZrO2 solid solutions. The oxygen vacancies play a key role in the activation of gaseous oxygen to form active oxygen species (Ox- species) for soot oxidation, and the lattice oxygen atoms also play a favorable role in the creation of highly active Ox- species. The surface-active Ox- species created by the surface lattice oxygen can immediately contact the soot and then rapidly promote the oxidation reaction. Hence, this work suggests that the cubic–tetragonal interfaces present in CeO2–ZrO2 solid solutions are also a relevant factor contributing to their excellent catalytic performance in diesel soot oxidation.