Gram-Scale Green-Synthesis of High Purity Pinacols and Amides by Continuous Tandem Photocatalysis via a Negative Carbon Emission Process.

Abstract

Solar-driven CO₂ reduction for practical applications confronts significant challenges, including the waste of oxidation power and the difficulty in isolating reduction products. Herein, a pre-coordination restriction strategy is presented to hierarchically assemble CdS quantum dots (QDs), cobalt sites and Zr₆ clusters in one metal-organic framework (MOF), resulting in the CdS@PCN-Co composite for simultaneous CO₂ photoreduction and C-C coupling. Impressively, the yields of CO and pinacols with CdS@PCN-Co can reach 59.5 mmol·g⁻¹ (99.4% selectivity) and 56.2 mmol·g⁻¹ (95.3% selectivity), respectively, over six and seven times higher than those with the CdS/PCN-Co mixture (9.8 mmol•g⁻¹ CO, 29.4% selectivity; 7.8 mmol•g⁻¹ pinacols, 22.7% selectivity). The superior catalytic performance of CdS@PCN-Co can be ascribed to the synergy among encapsulated CdS QDs, Zr₆ clusters and PCN-Co, where photogenerated electrons can efficiently transfer from CdS QDs to Co sites for selective CO generation while the remaining holes can oxidize the adsorbed 1-phenylethanol over Zr₆ surface to facilitate C-C coupling. More impressively, the released CO can be immediately used for carbonylation photosynthesis by immobilizing CdS@PCN-Co and Pd/PCN-Zn in a continuous-flow system with two reactors, which simultaneously achieves gram-scale photosynthesis of high-purity pinacols and amides by continuous tandem photocatalysis.