The role of adsorbed oxygen in formic acid oxidation by Pt/TiO2 facilitated by light pre-treatment

Abstract

Our study demonstrates that adsorbed oxygen species on Pt surfaces (PtO_ads) and active oxygen species (O⁻_ads) play a critical role in formic acid oxidation under the ambient condition in an aqueous suspension. The impact of light pre-treatment and dissolved oxygen concentration on the generation of surface oxygen species (PtO_ads and O⁻_ads) was studied using X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). A strong correlation between the formic acid oxidation rate and the surface oxygen species was observed. Light pre-treatment introduced a greater amount of PtO_ads and O⁻_ads compared with the untreated Pt/TiO₂ and, as a result, invoked an almost seven-fold increase in the formic acid oxidation rate. The amount of surface oxygen species was found to increase with increasing dissolved oxygen concentration in the system which also accelerated the formic acid oxidation rate. Additionally, the decreasing amount of PtO_ads at the end of the reaction with increasing initial formic acid concentration suggests that the oxygen species are important to, and consumed during, the oxidation process.