Influence of manganese oxide on the activity of Pt/Al2O3 catalyst for CO and n-hexane oxidation

Abstract

The influence of low loadings of MnOx on the catalytic activity for n-hexene and CO oxidation over highly dispersed Pt on alumina catalysts has been investigated. The applied deposition-precipitation method allows Mn to be deposited on the Pt containing egg-shell volume. The catalyst samples were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and selective CO chemisorption. Platinum influences the dispersion of deposited MnOx. The dispersion of the MnOx phase is higher on Pt containing samples than on Al2O3. The Pt decoration by Mn is reflected by a low CO uptake and the Pt oxidation state (Pt2+). The addition of Mn lowers the catalytic activity for CO oxidation. This is attributed to a change of the Pt sites such that adsorption of CO is less favorable. The activity of the catalysts in the oxidation of n-hexane showed a significant improvement with addition of MnOx. A light-off shift by about 40 degrees C was observed. This improvement is attributed to the formation of Mn-Pt oxide like species that primarily weakens the Pt-O bond.