Theoretical calculation of styrene hydrogenation over Pd2 and Pd2CO. Energy profiles for styrene hydrogenation on Pd2/TiO2(010) (black) and Pd2CO/TiO2 (010) (red). IS denoted as the coadsorption of styrene and H atoms, SHI represented the semihydrogenated intermediate, and FS stood for the gaseous ethylbenzene with the H-free surface. The key structures were illustrated in the black and red dashed frame. The blue, red, dark gray, and white balls represented Pd, O, C, and H atoms, respectively.