Dynamics of CO photooxidation to CO2 on rutile (110)

TL;DR

The paper studies how CO is rapidly converted to CO2 on rutile TiO2 using ultrafast laser techniques, revealing faster oxidation dynamics compared to anatase.

Contribution

The study identifies an O2-TiO2 charge transfer complex as the key to initiating CO oxidation on rutile TiO2 with faster dynamics.

Findings

CO2 is detected within 800±250 fs after laser excitation on rutile TiO2(110).

An O2-TiO2 charge transfer complex is proposed as the oxygen activation pathway for CO oxidation.

Rutile TiO2 shows faster oxidation dynamics than anatase despite anatase being more active overall.

Abstract

Free-electron lasers (FELs) enable the study of the ultrafast dynamics of photocatalytic reactions by time-resolved X-ray photoelectron spectroscopy (tr-XPS) with femtosecond time resolution. In an optical pump - soft X-ray probe photoemission experiment conducted at the free-electron laser in Hamburg (FLASH), we observed the ultrafast oxidation of CO to CO2 on rutile TiO2(110) by monitoring the O 1s core level region. Within 800± 250 fs after laser excitation, CO2 as a product of the photooxidation of CO is detected. Based on density functional theory calculations, we propose that the oxygen activation pathway for the CO oxidation is initiated via an O2-TiO2 charge transfer complex directly excited by the 770 nm pump laser. Our results give insight into the fundemental understanding of photocatalytic processes of TiO2 polymorphs relevant for the design of more efficient photoctalaysts.

The oxidation of CO to CO2 on rutile TiO2 is a model reaction in heterogeneous catalysis, but the effect of substrate-specific oxygen activation timescales remains underexplored. Here, the authors monitor the reaction through time-resolved photoelectron spectroscopy at a free-electron laser and propose an O2-TiO2 charge transfer complex responsible for initiating the oxygen activation pathway for CO oxidation on rutile, showing that despite anatase being the more active photocatalyst, oxidation dynamics on rutile are faster.

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