(676a) Impact of Pt Nuclearity on CO2 Reduction and Aldol Condensation Reactions

Today, significantly enhanced activity and/or selectivity have been reported on single-atom catalysts (SACs) that surpass those of nanoparticles for heterogeneous reactions. There is considerable evidence that the outstanding performance of SACs arises from a drastic modification of the electronic environment on the catalyst surface to bring in the new chemistry. To understand the structure-function relationships of metal oxide-supported Pt catalysts, especially to study the electronic feature and catalytic performance of sub-nanometer-sized Pt sites that have small atom numbers, we adjusted the geometry of Pt supported on Fe₃O₄ changing from single-atoms to rafts to nanoparticles gradually. The functionality and stability of the above-mentioned Pt geometries are tested on two different reactions: the reduction of CO₂ and the aldol condensation of acetone. Reactivities of CO₂ reduction and acetone aldol condensation were found to follow different trends in the presented structures. In the reaction of CO₂ reduction, the raft catalysts demonstrate the same turn-over-frequency (TOF) but significantly improved stability compared to the single atoms. In addition, the nuclearity of the Pt structures is found to be crucial in determining the phase transition and involvement of the Fe₃O₄ support in the CO₂ reduction. On the other side, the raft and nanoparticle catalysts cannot compete with the single atoms regarding the activity in the aldol-condensation reaction. A series of prevailing characterizations were performed on the synthesized Pt structures, and the results underline our hypothesis that doping Pt single atoms to the surface of Fe₃O₄ creates stronger Pt^δ+-O^2- pairs facilitating the acetone adsorption and α-H abstraction steps, which eventually results in the remarkable high activity of the Pt SAC in the self-coupling of acetone.