Ageing resistance of rhodium supported on CeO2-ZrO2 and ZrO2: Rhodium nanoparticle structure and Rh-support interaction under diverse ageing atmosphere

摘要

Rh/CeO2-ZrO2 and Rh/ZrO2 catalysts were prepared by impregnation method and aged in air and N-2 atmospheres at 1050 degrees C. The nanostructure, oxidation state, and redox properties of rhodium were characterized by X-ray diffraction, CO chemisorption, H-2 temperature-programmed reduction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalytic activity of the catalysts was evaluated by a (CO + NO) probe reaction. The oxidation state and sintering of rhodium nanoparticles were highly influenced by the support and ageing atmosphere. Rhodium species mainly existed as rhodium oxides after air ageing and as more active metallic rhodium after N-2 ageing. Owing to the Rh-support interaction, i.e., Rh-ceria or Rh-zirconia interaction, smaller rhodium particles were obtained in the air aged samples when compared with those in the N-2-aged samples. The presence of Rh-O-Ce bonds inhibited the sintering of rhodium particles, however, only in an oxygen-containing atmosphere and easily stabilized the high oxidation state of rhodium nanoparticles, leading to catalyst deactivation. Contrarily, Rh-zirconia interaction effectively inhibited the sintering of rhodium particles and preserved the low oxidation state of rhodium nanoparticles with high redox property as active reaction sites after ageing. Consequently, Rh/ZrO2 displayed superior ageing resistance than Rh/CeO2-ZrO2, thereby making ZrO2 a better support for rhodium than ceria-based supports in automotive three-way catalysts. (C) 2016 Elsevier B.V. All rights reserved.