UV-LED photocatalytic oxidation of carbon monoxide over TiO2 supported with noble metal nanoparticles

The TiO2 catalysts supported with 0.01–4 wt% Pt, Pd, or Au were prepared via chemical reduction of inorganic precursors with NaBH4 or their photoreduction in water-ethanol solution under UV irradiation. The samples were characterized by the means of X-ray fluorescence, N2 adsorption, TEM, XPS and UV-Vis spectroscopy and investigated in the processes of dark catalytic and UV-LED photocatalytic oxidation of carbon monoxide at room temperature. UV-LED irradiation of all the synthesized catalysts resulted in an increase in CO oxidation rate compared to the oxidation without UV. Two parallel pathways including thermal catalytic oxidation on metal particles and photocatalytic oxidation by the action of UV light were proposed for the M/TiO2 catalysts. The domed dependence of photocatalytic oxidation rate on the metal content was observed for all the metal deposited catalysts and had a maximum at 1 wt% for Pt and 0.05 wt% for Pd and Au. The activity of the 1 wt% Pt/TiO2 catalyst was 7 and 11 times higher than that of the 0.05 wt% Pd- and Au-loaded samples, respectively. For the 1 wt% Pt/TiO2 sample, the deposition method via chemical reduction with NaBH4 resulted in a much higher activity than the photoreduction method. The effects of the metal nature, its content and the preparation method on CO photocatalytic oxidation rate are discussed in the terms of metal particle size and charge state based on the data from TEM and XPS analyses.