The promoting effect of visible light on the CO + NO reaction over the Pd/N–TiO2 catalyst

Abstract

Herein, a Pd nanoparticle catalyst supported on N-doped TiO₂ (Pd/N–TiO₂) was prepared by a chemical reduction method and evaluated for catalytic performance in the CO + NO reaction with and without visible light irradiation. It was found that the Pd/N–TiO₂ catalyst exhibited excellent catalytic activity even at low temperatures, and upon introducing visible light, its catalytic performance was drastically enhanced. The results of in situ diffuse reflectance infrared Fourier transform spectra (in situ DRIFTS) indicated that visible light benefited the adsorption and activation of both NO (at N–TiO₂ sites) and CO (at Pd sites) as well as formation of active intermediates (e.g. Ti⁴⁺–NO⁻ and CO–Pd). On the basis of Raman spectroscopy, electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) results, it was proposed that Pd/N–TiO₂ possessed numerous surface oxygen vacancies (SOVs-Ti³⁺), and visible light irradiation could promote the generation of SOVs and increase in the Pd surface electron density by photo-induced electron (from N_2p to Ti_3d orbit) transfer from N–TiO₂ to Pd nanoparticles, resulting in enhanced adsorption and activation of CO and NO. Thus, a strengthened photo-assisted effect for the CO + NO reaction occurred on Pd/N–TiO₂.