Kinetics of hydrogen chemisorption on high surface area Pd/Ce 0.8Zr 0.2O 2

Abstract

The effect of pre-reduction conditions on the H 2 chemisorption kinetics of high surface area Pd(0.53 wt.%)/Ce 0.8Zr 0.2O 2 was investigated by means of temperature-programmed reduction, oxygen-storage capacity, IR spectroscopy and volumetric hydrogen measurements. In the 20–80 ° C range, the pre-reduction rate was very fast and dependent on temperature, with an apparent activation energy of 58 kJ mol −1. Distinction between PdO reduction and H spillover processes is only possible at low H 2 pressures. The total H 2 uptake and the chemisorption rate strongly decrease by the use of high H 2 pressures during the pre-reduction process. Irreversible reduction with the concomitant oxygen vacancies formation occurs at low temperature, as demonstrated by in situ IR experiments. However, H 2 uptake on the Pd(0.53 wt.%)/Ce 0.8Zr 0.2O 2 during pre-reduction and chemisorption is recovered by reoxidation at 400 ° C.