Structure Sensitivity and Hydration Effects in Pt/TiO 2 and Pt/TiO 2 –SiO 2 Catalysts for NO and Propane Oxidation

The NO and propane oxidation activities of a series of 1%Pt/TiO 2 –SiO 2 catalysts show different underlying trends as the support composition changes. Surface characterisation of the catalysts indicates that the trend for NO conversion is consistent with the oxidation rate being dependent on the degree of metallic character of the Pt nanoparticles, rather than their morphology. Although a similar correlation is expected for the total oxidation of propane, it is masked by the effects of adventitious ions originating during manufacture of the support materials. When residual chloride is present in the support, most of the exposed Pt is stabilised in its low-activity ionic form; while support materials containing W or oxidised-S ions give rise to catalysts with much higher activity than expected from their measured Pt 0 content. When a Cl-containing, but SiO 2 -free, TiO 2 support material is pre-treated hydrothermally, the propane-oxidation activity of the resultant Pt/TiO 2 catalyst is substantially improved, so that it matches the performance of highly-metallic Pt supported on TiO 2 containing 16 wt% SiO 2 . The hydrothermal pre-treatment removes residual chloride from the support material, but it also leaves the catalyst in a hydrated state. We show that, by controlling the metallic content of Pt nanoparticles, understanding the promoting and inhibiting effects of adventitious ions, and optimising the degree of catalyst hydration, the activity of 1%Pt/TiO 2 –SiO 2 catalysts can be made to exceed that of a benchmark 2%Pt/γ-Al 2 O 3 formulation for both NO and propane oxidation.