Enhanced catalytic activity induced by defects in mesoporous ceria nanotubes

Abstract

Mesoporous ceria nanotubes are fabricated by the following process: ceria was deposited on the surface of ZnO nanorods by the ultrasonic assisted successive ionic layer adsorption and reaction (SILAR) method to obtain ceria/ZnO composite nanostructures, then, the ZnO core was removed by HNO₃ solution, resulting in the formation of ceria nanotubes, which have the large surface area of 109 m² g⁻¹. Such ceria nanotubes have excellent catalytic performance in the CO → CO₂ conversion, and the reaction start temperature is about 100 °C lower than that of commercial ceria (CeO₂) particles. The specific catalytic activity of the ceria nanotubes is 9 times higher than that of commercial ceria particles at 320 °C. The XPS and Raman investigations have proved that the Ce³⁺ ion number in the surfaces is about 23% of total cerium ion number, which may be responsible for the high reduction performance to oxygen. The positron annihilation experiments prove that a large amount of vacancies and vacancy groups exist in these samples. A large amount Ce³⁺ formation is closely associated with these vacancies and vacancy groups. Temperature programmed reduction (H₂-TPR) experiments further confirm that the enhanced activity of mesoporous ceria is in contrast to commercial ceria particles. Moreover, for ceria nanotubes the enhanced activity is attributed to enhancement of the surface activity caused by Ce³⁺ ions. The catalysis activity stability arises from contribution of the cycle transition between Ce³⁺ and Ce⁴⁺ ions.