On the selectivity of CO2 photoreduction towards CH4 using Pt/TiO2 catalysts supported on mesoporous silica

Pt/TiO2 and Pt/TiO2-COK-12 photocatalysts have been prepared by a deposition-precipitation method and characterized by means of X-ray diffraction (XRD), N2 adsorption isotherms, transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and inductively coupled plasma optical emission spectrometry (ICP-OES). The photocatalytic activity of as-prepared photocatalyst was tested for the photocatalytic reduction of CO2 under UV light in a continuous flow gas-phase photoreactor. CH4 and CO were detected as major carbon products for all photocatalysts, with minor amounts of CH3OH. Carbon monoxide is the main product obtained over TiO2 regardless of the presence of COK-12 as a mesoporous support, whereas Pt leads to CO2 reduction towards CH4 formation, with a selectivity that reaches ca. 100% with optimum loading. Supporting the Pt/TiO2 catalysts on COK-12 preserves the selectivity of the reaction towards CH4 and further improves the overall activity of the Pt/TiO2 materials. After-reaction attenuated total reflection infrared spectroscopy (ATR-IR) and in-situ near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) have been employed to identify reaction intermediates and used to explain the observed selectivity trends.