Correlation of the ratio of metallic to oxide species with activity of PdPt catalysts for methane oxidation

Bimetallic catalysts consisting of Pd and Pt on TiO2-zeolite (mordenite, beta, ZSM-5) supports were prepared and tested for the combustion of methane. The activity of the catalysts was found to be dependent on the zeolite topology and SiO2 : Al2O3 ratio and was linearly dependent on the proportion of Pd and Pt present in a bimetallic phase observed in XRD diffractograms of the catalysts. This linear dependence was valid for a range of zeolites used. STEM-EDS and electron tomography showed the Pd and Pt to be largely co-located and XAS and XPS indicated that the metals are mostly present in the form of oxide nanoparticles with a minor contribution from the metals at high SiO2 : Al2O3 ratios. Catalyst characterization showed there to be little difference overall in the metal loading and physical characteristics of the samples and NH3-TPD suggested that the activation of methane over acid sites is not important. Adding water to the feed, slightly reduced the conversion but did not affect the deactivation profile of the catalysts tested