PNNL

Abstract

In this study, we investigated the effect of the support (rutile vs anatase titania) and of the Pt size of Pt nanoparticles and supports (rutile vs anatase) in the CO oxidation reaction. The steady-state specific activity of Pt/Rutile gradually increases with Pt dispersion, while that of Pt/Anatase is invariant with respect to Pt dispersion and is lower than the activity of Pt/Rutile. Our kinetic studies demonstrated that the reaction order for CO based on steady state is positive for sub-nm Pt clusters stabilized on rutile titania and it gradually changes to zero for large Pt clusters (>1 nm), as known in agreement with other studies for for supported Pt catalysts. In contrast, Pt/Anatase catalysts always show zero order dependence irrespective of Pt the size of Pt nanoparticles. Scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS) and CO chemisorption results confirm that the notable sintering of sub-nm Pt clusters supported on anatase occurs with time-on-stream, which we correlate with might be related with the change of the CO reaction order from positive (order initially) tobut zero order for larger particles after sintered states. On the contrary, Pt/Rutile does not show serious sintering during the reaction, and it shows positive reaction order even during the steady state. Thus Pt/Rutile shows positive order at steady state and higher specific activity. Our study reveals the origin of profound catalytic differences between Pt nanoparticles supported on anatase and rutile titania and highlights better stability and activity of Pt/Rutile catalysts. than Pt/Anatase due to its better stability.