Abstract
In this work, we first report synthesizing a series of single-atom metals (covering main-group, transition, precious, and rare earth metals) photocatalysts M_(SA)/TiO2 using a simple, efficient, and high-yield mechanochemistry (high-energy ball milling) and evaluate their efficiency towards CO2 photoreduction. In the synthesized single-atom catalyst (SAC), the CH4 yield from CO2 photoreduction using Pd_(SA)/TiO2 reaches as high as 271.6 μmol·g~(-1)·h~(-1) with the selectivity of ～98.0%, far surpassing those of conventional Pd clusters and nano-particles. The experimental results and density functional theory (DFT) calculations reveal that the strong adsorption at single-atom catalytic sites (Pd) leads to significant bending of O=C=O bond angle from 180.0 to 151.0 ° and length from 1.16 to 1.20 A. The induced deformation greatly 'energizes' the CO2, thus reducing the kinetic energy barrier significantly and offering high catalytic activity. Meanwhile, combined with in-situ Fourier-transform infrared (FT-IR), a rational reaction pathway of CO2 photoreduction over efficient SACs is proposed.
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