Three-dimensionally ordered macroporous Ce0.8Zr0.2O2-supported gold nanoparticles: synthesis with controllable size and super-catalytic performance for soot oxidation

Abstract

A series of catalysts of three-dimensionally ordered macroporous (3DOM) Ce_0.8Zr_0.2O₂-supported gold nanoparticles with controllable sizes were successfully synthesized by the facile method of gas bubbling-assisted membrane reduction (GBMR). All the catalysts possess well-defined 3DOM structures, which consist of interconnected networks of spherical voids, and the Au nanoparticles are well dispersed and supported on the inner wall of the uniform macropore. The relationship between Au particle sizes and the ability to adsorb and activate oxygen was characterized by means of O₂-TPD and XPS. The results show that the active oxygen species (O⁻) and gold ions with oxidation state of Au⁺ are essential for soot oxidation reaction. 3DOM Au_0.04/Ce_0.8Zr_0.2O₂catalyst with Au particle size of 2–3 nm has the strong capability of adsorption and activation of oxygen. Thus, it exhibits super-catalytic activity for diesel soot oxidation, especially at low temperature. The reaction pathways of catalytic soot oxidation in the presence or absence of NO can be outlined as follows: at low temperature (<250 °C), the catalytic performance of supported Au catalyst is dependent on the Au particle sizes. At relatively high temperature (>250 °C), the catalytic activity is strongly related to the NO gas, because NO₂ derived from NO oxidation is used as intermediate to catalyze soot oxidation.