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Mesoporous silica (SBA-15) loaded with TiO x species was synthesized by anhydrous grafting of titanium isopropoxide, and a novel procedure for the preparation of ZnO x /SBA-15 materials by grafting of Zn(acac) 2 was explored.The TiO x /SBA-15 and ZnO x /SBA-15 materials as well as subsequently prepared bifunctional ZnO x -and TiO x -containing SBA-15 materials were characterized in depth by combining N 2 physisorption measurements, UV−vis, X-ray photoelectron and Xray absorption spectroscopy, and CO 2 and NH 3 temperatureprogrammed desorption experiments. The characterization results confirmed a close proximity of ZnO x and TiO x in the subsequently grafted materials. Because of strong interactions between the Zn precursor and the SiO 2 surface, the order of the ZnO x and TiO x grafting steps affected the amount of Ti−O−Zn bonds formed in the materials. When ZnO x is present in SBA-15, subsequently grafted TiO x is higher coordinated and more Ti−O−Zn bonds are formed compared to SBA-15 in which TiO x was introduced first, indicating strong interactions between the Ti precursor and ZnO x . While all TiO x and ZnO x -containing samples exhibit a large amount of acidic sites, ZnO x present as isolated species or small clusters in SBA-15 significantly improves the CO 2 adsorption capacity by introducing basic sites. In the subsequently grafted samples the amount of acidic and basic sites is found to be unaffected by the order in which the two transition metals are introduced.

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Newly developed tubular reactor geometry allows intensive gas–solid interaction in photocatalytic gas-phase CO2 reduction.

Quantitative reactivity determinants imply that P25-TiO2 has limited applicability in heterogeneous photocatalytic CO2 conversion in the gas-phase.