Probing surface oxide formations on SiO2-supported platinum nanocatalysts under CO oxidation

Abstract

Formations of an ultrathin oxide layer on noble metal catalysts affect the characteristics of fundamental molecular behaviours such as adsorption, diffusion, and desorption on their surfaces. That is directly correlated to enhancement of catalytic activity under operating conditions because the kinetics of catalytic reactions are also simultaneously influenced. Especially, a sub-monolayered surface oxide is known as having a key role for improving catalytic activity, but revealing its existence in catalysis is challenging due to their fast chemical conversion. Herein, we report the first evidence of surface oxide formations on platinum (Pt) nanocatalysts under CO oxidation probed with a diffuse reflectance infrared Fourier transform (DRIFT) technique. Spectroscopic information demonstrates that the abrupt blue shift of adsorbed CO molecules vibrational frequencies of CO stretching mode on the reduced Pt nanocatalyst surface is initiated prior to aggressive CO conversion to CO₂ gas molecules. Site-specific replacements of the adsorbed CO molecule with dissociative oxygen occur just before the ignition temperature that is supposed to be an important reaction step for CO oxidation over a Pt nanocatalyst. Density functional theory (DFT) calculation results support this phenomenon as a function of relative atomic fractions between CO and O on a Pt model surface and consistently show a similar trend with experimental evidence.