Unveiling the promoting effect of water on formaldehyde oxidation over Pt/TiO2: insights from H/D kinetic isotope effect, in situ FTIR, and DFT

Abstract

Formaldehyde (HCHO), a prevalent indoor volatile organic compound, poses significant health risks to humans even at very low concentrations. As a result, its efficient degradation at room temperature is of utmost importance. However, the detailed mechanism for catalytic oxidation of formaldehyde remains unclear, particularly regarding the role of water vapor, which has been subject to considerable debate. In this study, we synthesized Pt-supported TiO₂ glass fiber catalysts (Pt/TiO₂ GF) via NaBH₄ reduction to investigate the reaction pathways and clarify the influence of water vapor on the oxidation process. The reaction mechanism and intermediates were systematically studied at room temperature using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), kinetic isotope effect (KIE) analysis, and density functional theory (DFT) calculations. Results revealed a clear reaction pathway of HCHO → DOM → HCOO⁻ → CO₂, with formate C–H bond cleavage (HCOO⁻* + O* → CO₂ + OH*) identified as the rate-determining step. Both experimental KIE results and theoretical calculations confirmed that water vapor substantially reduces the activation barrier for this step, significantly promoting formate decomposition and subsequent CO₂ formation. This work provides critical insights into the role of water in enhancing formaldehyde oxidation and offers theoretical support for developing efficient catalysts suitable for humid environments.