Wet air oxidation of acetic acid over platinum catalysts supported on cerium-based materials: Influence of metal and oxide crystallite size

Abstract

Platinum catalysts (2.5 wt%) prepared by impregnation on pure commercial ceria and on Zr 0.1(Ce 0.75Pr 0.25) 0.9O 2 sol–gel mixed oxide were synthesized and used for catalytic wet air oxidation (CWAO) of acetic acid. The influence of the platinum sintering (reducing treatment) was studied for both supports to modify the oxygen transfer from the gas phase onto the metallic active site of the catalyst and also to determine the effect of this treatment on the catalytic activity and stability. The catalysts were characterized by BET, TEM, XRD, FT-IR and hydrogen chemisorption before and after CWAO reaction, and oxygen storage capacity (OSC) was measured. The nature of the support [CeO 2 and Zr 0.1(Ce 0.75Pr 0.25) 0.9O 2 compounds] and the preparation conditions led to samples displaying a Pt dispersion ranging from 0.4 to 41%, and BET surface area varying from 4 to 45 m 2 g −1. The results demonstrate poisoning of the catalysts during the CWAO experiments due to the formation of carbonate species. This limits the performance of the mixed oxide-based catalysts displaying the highest OSC values. A correlation was established between the OSC of the catalysts and the formation of carbonate species. Nevertheless, there is no correlation between OSC and catalytic activity, with the ceria-based samples showing the highest reaction rate. An optimal platinum crystallite size is required to achieve the highest conversion of acetic acid in terms of turnover frequency values.