Reactivity of TiO2 Nanotube-Supported Platinum Particles in the CO Oxidation Reaction

Abstract

The CO oxidation on different platinum model catalysts, in particular differently sized Pt particles on vertically aligned TiO2 nanotubes (d=80, l=200 nm) was investigated by near-ambient-pressure X-ray photoelectron spectroscopy and simultaneous online gas analysis. The results are compared to the behavior on a TiO2(1 1 0) rutile crystal with a similar Pt coverage and a Pt(1 1 1) single crystal. Temperature-programmed reaction experiments at total pressures of 10−3 to 1.0 mbar, and a CO/O2 ratio of 1:4 were performed to evaluate the reactivity of the samples. The onset temperature of the reaction on the Pt/TiO2 nanotube samples was found to be lower than on Pt(1 1 1) and Pt/TiO2(1 1 0) and to decrease with decreasing particle size. For all particle samples, a steep increase in reaction rate at a defined temperature was observed, and at high temperatures the reaction became mass transfer-limited in all cases. Isothermal measurements showed that no CO is adsorbed on the particles when CO oxidation has a high activity and metallic platinum is the active catalyst. Ageing of the TiO2-supported samples is observed resulting in changes of the reaction onset and CO conversion.