Influence of Pt particle size and reaction phase on the photocatalytic performances of ultradispersed Pt/TiO2 catalysts for hydrogen evolution
Résumé
Pt/TiO2 photocatalysts were prepared by incipient wetness impregnation followed by oxidative and/or reductive thermal treatments. By varying the TiO2 form (commercial P25 and P90, and homemade shape-controlled), the Pt loading (0.2-1 wt% Pt) and the treatment temperature (200-600 °C), it has been possible to tune the Pt cluster size. An increase in the ethanol dehydrogenation rate under ultraviolet irradiation as the Pt cluster average diameter decreases from 17 to 9 Å is suggested by our data. Whereas pre-reduction in H2 leads to Pt clusters, pre-calcination in air leads to atomically
dispersed cationic Pt species. The former are more active and stable than the latter. This conclusion is valid both in gas- and liquid-phase reaction conditions for given TiO2 type and Pt loading. The activity results are consistent with a recent theoretical work showing that 1 nm is an optimal Pt cluster size for favoring both photoelectron transfer from TiO2 to Pt and hydrogen coupling on Pt. The best catalytic performance is obtained in gas phase for pre-reduced 0.2 wt% Pt/TiO2-P90, with an H2 production rate of 170 mmol h-1 gcat-1
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