Preparation of nanostructured CeO2-ZrO2-based materials with stabilized surface area and their catalysis in soot oxidation

Abstract

By using different precipitants to control the crystallization rate, a set of nanostructured CeO2-ZrO2-based materials with varying crystallite size, textural properties and thermal stability were synthesized, and were employed in soot catalytic oxidation. We investigated the physic-chemical properties of the materials using complementary techniques, including DSC-TGA, TEM, N2 adsorption-desorption, XRD, XPS and Hydrogen-Temperature Programmed Reduction (H2-TPR). The results indicated that the decompositions of hydroxides (M(OH)x) and carbonates (M(CO3)y) generated small and large oxide grains, respectively. Thus, the thermal stability was enhanced with increasing (NH4)2CO3 concentration, considering that the specific surface area and pore volume increased from 33 (CZ-Na) to 52 m2·g−1 (CZ-C5a) and from 0.15 to 0.34 ml·g−1, respectively, after aging at 1000 °C for 4 h. Although CZ-Na exhibited the preferable lattice oxygen mobility, it showed the worst soot oxidation activity, resulting from its sharp declined surface area and a lack of surface available oxygen. In contrast, CZ-5a with the largest amount of total surface available oxygen showed the optimal catalytic performance. Moreover, nearly no deterioration of activity was detected in CZ-5a after a long-term stability test. Therefore, soot oxidation is a surface-dependent reaction, and CeO2-ZrO2 catalyst design for this purpose should allow for stabilized high surface area.