A series of Ce-doped TiO 2 nanoparticles were prepared by a sol−gel process and characterized by XRD, SEM, TEM, EDX mapping, UV−vis DRS, Raman spectroscopy, N 2 adsorption−desorption, PL spectra, CO 2 -TPD, and XPS. It is found that Ce ions can enter the lattice matrix of TiO 2 and occupy of Ti sites. This atom replacement leads to the formation of impurity energy levels in the band gap of TiO 2 , extending light absorption into the visible light region. Because Ce has a more flexible valence state, both Ce 3+ and Ce 4+ could be formed in the composites. The preference facilitates the photoinduced charge separation inside of the crystals. Moreover, Pd nanoparticles were then loaded as a co-catalyst on the surface of doped composites. As the trapping center of electrons, it can efficiently adsorb and activate CO 2 molecules, promoting their transformation into CH 4 . These composites were then evaluated as photocatalysts for CO 2 hydrogenation. While all of them could efficiently catalyze the reaction, 1.0% Pd/ 0.5% Ce-TiO 2 catalysts show the best photocatalytic performance, with CH 4 and CO yields up to 220.61 and 27.36 μmol/g, respectively, under visible light irradiation of 3 h. The improved photocatalytic behavior could be possibly induced by the synergistic effect between Ce and Pd. A probable mechanism was thus proposed based on above characterizations and experimental results.

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