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/TiO 2 catalyst was studied by in situ Fourier transform IR and time-resolved IR spectroscopy. For the Pt/TiO 2 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 TiO 2 for methanol adsorption. Surface species CH 2 O(a), CH 2 OO(a), and HCOO(a) are derived from the photocatalytic reaction of methanol on Pt/TiO 2 . The increase of gas-phase methanol or water accelerates the photoreaction and improves the activity of H 2 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 TiO 2 -based photocatalysts after band gap excitation. The decay rate of the long-lived electrons correlates well with the activity of H 2 production. These results show that the long-lived electrons contribute to the H 2 generation and the decays of the long-lived electrons on millisecond to second time scale in Pt/TiO 2 are ascribed to the reaction for H 2 evolution: e tr -[Pt] + H + fH‚f1/2H 2 . The function of the molecularly adsorbed methanol or water is found to mediate the proton transfer on the TiO 2 surface. The activities of H 2 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 H 2 production.

Effects of Zn2+ and Pb2+ dopants on the activity of Ga2O3-based photocatalysts for water splitting

“…In other words, the photogenerated electron decay becomes much slower and faster for b-Ga 2 O 3 doped with Zn 2+ and Pb 2+ ions, respectively. The number of electrons not yet recombined can be estimated by the absorbance, [43][44][45] so the above observation also indicates that there are more long-lived photogenerated electrons survived from the fast recombination in the Zn-doped b-Ga 2 O 3 sample and less in Pb-doped b-Ga 2 O 3 .…”

“…The kinetics of the carrier for the surface can be examined on the sample in methanol vapor. 43,44,46 Fig. 8b shows the IR absorbance in 3 Torr of methanol vapor.…”

Ultrafast Carrier Dynamics in Exfoliated and Functionalized Calcium Niobate Nanosheets in Water and Methanol

“…Our results indicate that reduced surface recombination is responsible for a long-lived charge separation, in agreement with a long-lived charge separation observed in clay-niobate materials under steady-state illumination. 52 We also observed a sub-nanosecond loss of electrons in [H 1-x 28,53 Photocatalysis and EPR studies are currently in progress to identify the process responsible for the loss of electrons.…”

A novel TiO2 with a large amount of bulk intrinsic defects—Visible-light-responded photocatalytic activity induced by foreign trap

“…However, this doubt was denied after the transient IR absorption spectra of both P25-TiO 2 and novel TiO 2 (A) were determined. The transient IR absorption of 1000-3000 cm 1 is a powerful tool for investigating the lifetime of the photo-generated electrons in the conduction band [35][36][37]. …”