Redox Dynamics of Rh Supported on ZrP2O7 and ZrO2 Analyzed by Time-Resolved In Situ Optical Spectroscopy

Abstract

In situ time-resolved diffuse reflectance spectroscopy was first applied to supported Rh catalysts (0.4 wt % Rh/ZrO2 and Rh/ZrP2O7) under dynamic three-way catalysis conditions fluctuating between fuel-lean and fuel-rich gas atmospheres. The optical absorption at 650 nm was found to decrease upon lean-to-rich switching of the gas feed, which led to the reduction of Rh oxide (Rh3+) to metallic Rh (Rh0), followed by a reversible increase upon back switching rich-to-lean. The kinetic analysis suggested that the reduction of Rh3+ to Rh0 was faster than the reoxidation over Rh/ZrP2O7, whereas the reduction was comparable with or slower than the reoxidation over Rh/ZrO2. The activation energy of Rh/ZrP2O7 for the reduction, 13.6 kJ mol–1, was smaller than that for the oxidation, 48.7 kJ mol–1, which contrasted with those of Rh/ZrO2 (21.4 and 34.1 kJ mol–1, respectively). These results were closely associated with the higher NO reduction activity of Rh/ZrP2O7 than Rh/ZrO2 under a lean-gas atmosphere because Rh w...