Photocatalytic H2 production on Pt/TiO2–SO42− with tuned surface-phase structures: enhancing activity and reducing CO formation

Abstract

Photocatalytic reforming of biomass is a promising way to produce hydrogen using renewable energy. Photocatalytic reforming of methanol on Pt/TiO₂–SO₄²⁻ as a model reaction of biomass reforming was investigated. Sulfated TiO₂ (TiO₂–SO₄²⁻) with a tunable surface phase was prepared by calcining commercially available titanium dioxide TiO₂ (Degussa P25) with deposited sodium sulfate Na₂SO₄ as a modifier. Compared with P25, the as-prepared TiO₂–SO₄²⁻ with Pt co-catalyst shows an increase up to 6-fold in the activity for H₂ production via photocatalytic reforming of methanol, and the CO (undesired product) concentration in the produced H₂ is decreased by about two orders of magnitude. XRD patterns and UV Raman spectra clearly indicate that TiO₂ depositing with Na₂SO₄ can significantly retard the phase transformation from anatase to rutile during calcination at elevated temperatures. It is proposed that both the phase composition and the high crystallinity of TiO₂ contribute to the high H₂ evolution activity. IR spectra of pyridine adsorption and the NH₃-TPD profile show that the surface acid sites of the photocatalyst are greatly reduced after calcination at high temperatures. It is proposed that the decrease in the acidity of the samples might be responsible for the low CO selectivity.