Gas-Phase Photocatalytic\nCO<sub>2</sub> Methanation\nover Ru/TiO<sub>2</sub>: Effects of Pressure, Temperature, and Illumination

This\nwork examines the effects of temperature (100–150 °C),\npressure (1–25 bar), and UV illumination on gas-phase photocatalytic\nCO<sub>2</sub> methanation over Ru/TiO<sub>2</sub>. Irradiating the\ncatalyst enables an ∼20% decrease in operating pressure to\nmaintain the same production rate. Furthermore, the relative light\nenhancement is greater at 100 °C than 150 °Ca phenomenon\nattributed to increased carrier recombination rates at higher temperatures.\nArrhenius experiments indicate that the global activation energy (<i>E</i><sub>a</sub>) of the reaction is similar in the dark and\nlight, suggesting that rate enhancements are determined by changes\nin surface coverage. To test this hypothesis, the CO<sub>2</sub> reduction\nmechanism is probed using <i>in situ</i> diffuse reflectance\ninfrared Fourier transform spectroscopy (DRIFTS). The spectra show\nan increase in the relative surface coverage of the intermediate formyl\ngroup under irradiation. These findings illustrate that, within the\nexperimental conditions explored in this study, the photoexcitation\nof charge carriers in the semiconductor primarily influences the surface\ncoverage of intermediates to drive enhanced methane formation at low\ntemperatures.