Mechanistic Studies of Photocatalytic Reaction of Methanol for Hydrogen Production on Pt/TiO₂ by in situ Fourier Transform IR and Time-Resolved IR Spectroscopy

Abstract

The anaerobic photocatalytic reaction of methanol on Pt/TiO2 catalyst was studied by in situ Fourier transform IR and time-resolved IR spectroscopy. For the Pt/TiO2 catalysts reduced at high temperature, the capacity of methanol adsorption decreases with the increase of the Pt loading, indicating that Pt particles or atoms occupy some of the active sites on TiO2 for methanol adsorption. Surface species CH2O(a), CH2OO(a), and HCOO(a) are derived from the photocatalytic reaction of methanol on Pt/TiO2. The increase of gas-phase methanol or water accelerates the photoreaction and improves the activity of H2 production. When the catalysts are exposed to methanol, the strong electronic absorption on nanosecond to second time scale is observed, indicating that a great amount of long-lived electrons are produced in TiO2-based photocatalysts after band gap excitation. The decay rate of the long-lived electrons correlates well with the activity of H2 production. These results show that the long-lived electrons contribute to the H2 generation and the decays of the long-lived electrons on millisecond to second time scale in Pt/TiO2 are ascribed to the reaction for H2 evolution: etr-[Pt] + H+→H·→1/2H2. The function of the molecularly adsorbed methanol or water is found to mediate the proton transfer on the TiO2 surface. The activities of H2 production under steady-state irradiation conditions were also measured, and it is deduced that the yield of the long-lived electrons could be responsible for the activity of H2 production.