CO oxidation on SnO2 surfaces enhanced by metal doping
Doping metal atoms into a host metal oxide lattice can enhance its catalytic activity by modulating the properties of surface oxygen. Here, Pt-doped antimony–tin oxide (Pt/Sb–SnO2) was compared with Pt-deposited tin oxide (Pt/SnO2) and Pt-deposited silica (Pt/SiO2) for the oxidation of CO and propylene. 0.1 wt% Pt was deposited in all three cases. High angle annular dark field scanning transmission electron microscopy images, diffuse reflectance infrared Fourier transform spectra, pulsed H2 chemisorption results, and X-ray photoelectron spectra indicated that Pt/Sb–SnO2 has atomically doped Pt inside the SnO2 lattice while Pt/SnO2 has Pt nanoparticles covered with SnO2 layers and Pt/SiO2 has Pt nanoparticles exposed at the SiO2 surface. Pt/Sb–SnO2 showed the best activity for CO oxidation but the poorest activity for propylene oxidation. Propylene oxidation occurred the least on Pt/Sb–SnO2 due to the lack of surface Pt sites. CO temperature-programmed reduction and O2 temperature-programmed desorption results revealed that surface oxygen is the most active on Pt/Sb–SnO2. The formation of carbonates during CO oxidation was monitored, and Pt/Sb–SnO2 showed the least amount of surface carbonates with enhanced activity and durability. Doping a minimal amount of precious metal can be an efficient strategy to control the properties of metal oxide catalysts.