Platinum nanoparticle modulated titania electronic structure descriptors for selective photocatalytic CO2 conversion

[Display omitted] •Electronic structure (ES) of TiO2 is modulated by feature of deposited Pt NPs.•dz2/dx2-y2 is an ES descriptor of TiO2 for photocatalytic CO2 conversion to CH4.•Adsorption energy of CO on TiO2 is also an ES descriptor for CH4 selectivity.•t2g/eg of TiO2 is an ES descriptor for H2 selectivity of CO2 photoreduction.•Adsorption energy of H on TiO2 is also an ES descriptor for H2 selectivity. Modulation of the electronic structure of TiO2 nanorod array (NR), which governs the selectivity for the photocatalytic CO2 conversion, is demonstrated by the deposition of Pt nanoparticles (NPs) with various configurations. In-situ X-ray absorption near edge structure (XANES) measurements suggest that the active sites for the photocatalytic reaction are located on the surface of TiO2 NRs, but not on the Pt NPs, because the photocharge transfer from TiO2 NRs to Pt NPs is inefficient. The t2g/eg orbital ratio and dz2/dx2-y2 orbital ratio of TiO2 acquired from Ti L3-edge spectra of the Pt NP/TiO2 NR photocatalysts, which are strongly influenced by the feature of the deposited Pt NPs, are respectively well-correlated to the experimental selectivity of H2 and CH4 for photocatalytic CO2 conversion as well as the density functional theory calculated adsorption energies of H atom and CO molecule on the TiO2 surface. The Pt NPs thus play a crucial role as a promoter rather than as a cocatalyst. Besides the adsorption energies of H and CO on TiO2, the t2g/eg and dz2/dx2-y2 ratios of Ti 3d unoccupied state can be the electronic structure-based descriptors of TiO2 heterostructures for photocatalytic CO2 conversion to distinguish between H2 evolution and CH4 formation.