Controlled manipulation of CO oxidation rate on Pt/anatase via the schwab effect

Abstract

Difficulties in achieving control over carrier concentration have impeded progress toward tailoring the carrier concentration (i.e., electron richness) in semiconducting oxide supports for metal catalysts. Such tailoring could make possible the intentional exploitation of the Schwab effect, in which the carrier concentration in the semiconducting support affects reaction rate on the metal catalyst. The present work demonstrates such principles using the model case of CO oxidation over Pt supported on anatase TiO2 grown by atomic layer deposition. The carrier concentration in the polycrystalline semiconductor is controlled over a factor of 10 via an unconventional means - film thickness, which indirectly influences the concentration of electrically active donor defects at grain boundaries. Over this range, the reaction rate constant varies by about a factor of 2 depending upon the ratio of reactants, and is rationalized by electron injection from the support into Pt according to a standard d-band filling model. Electrical characterization of the films by capacitance-voltage measurements, together with photoelectron spectroscopy of the metal, fleshes out this picture.