ZnxZrO2+x-Based Photocatalyst with Dual Active Sites for Tunable Syngas Production from CO2 Photoreduction

Abstract

Photocatalytic reduction of CO2 in H2O to CO and H2 for syngas production is an attractive option to solve global warming and generate a feedstock for the Fischer–Tropsch process. The syngas generated from CO2 photoreduction with a precise and controllable ratio of H2/CO remains a major challenge to date. In this work, CdS-sensitized nanoscale ZnxZrO2+x solid solutions with dual active sites were synthesized as photocatalysts for tunable syngas H2 and CO production from CO2 photoreduction. The staggered band energy alignments, electron paramagnetic resonance results, and the site of palladium/gold nanoparticles by photodeposition indicate that the charge transfer in the CdS/ZnxZrO2+x heterojunction mainly follows the conventional type II mechanism. Density functional theoretical calculation results reveal that Zn and Zr sites on ZnxZrO2+x are favorable for the adsorption of H2O and CO2 molecules and generation of H2 and CO, respectively. The H2/CO ratio can be controlled in the range from 0.9 to 25.0 by adjusting the content of Zn in ZnxZrO2+x. Moreover, syngas production can be further improved by the modification of Pd nanoparticles. For the first time, this work proposes a strategy to construct a photocatalyst with dual active sites for effectively controlling the H2/CO ratio in syngas synthesis through a fundamental understanding of adsorption and catalytic reaction sites in both H2 evolution and CO2 reduction reactions.