Time-dependent evolution of morphologies and lattice defects in hydrothermal synthesized ceria-zirconia solid solutions for catalytic combustion of diesel soot

Abstract

In this work, the physical-chemical and morphological evolution of CeO₂-ZrO₂ solid solutions caused by hydrothermal processing time, and its effects on catalytic diesel soot elimination were studied. SEM and TEM results show that the CeO₂-ZrO₂ nanocrystal particles gradually aggregate with the extension of hydrothermal processing time. A moderate hydrothermal processing time can facilitate the engineering of catalyst morphology at micronmeter scale, however, excessive hydrothermal synthesis time would contrarily destroy the micrometer scaled catalyst morphological structure. The result of XPS, O₂-TPD and H₂-TPR analysis indicates that the hydrothermal synthesis process is conducive to generating lattice defects (oxygen vacancies) of CeO₂-ZrO₂ solid solution. This is a key factor for enhancing the concentration of surface-active oxygen species. The CeO₂-ZrO₂ catalyst prepared by 48 h of hydrothermal processing time (CZ-48 h) exhibits the highest concentration of surface-active oxygen species and oxygen vacancies. Interestingly, the CeO₂-ZrO₂ catalyst synthesized by 6 h of hydrothermal processing time (CZ-6 h) exhibits oxygen vacancy and surface-active oxygen levels that are close to the CZ-48 h, which is obviously more than the traditional co-precipitation CeO₂-ZrO₂ catalyst (CZ-0 h). The soot catalytic elimination performance of the CZ-6 h is also significantly superior to that of the CZ-0 h catalyst. Therefore, this study suggests that the short-time hydrothermal processing is an effective and low-cost strategy to create more oxygen vacancies and improve catalytic performance of CeO₂-ZrO₂ solid solution.