Gas-Phase Reactions of Carbon Dioxide with Copper Hydride Anions Cu₂H₂^–: Temperature-Dependent Transformation

Abstract

The hydrogenation of carbon dioxide into value-added chemicals is of great importance for CO2 recycling. However, the underlying mechanism of CO2 hydrogenation remains elusive owing to the lack of experimental evidence for the formation of the C–H bond. Herein, the gas-phase reaction of copper hydride anion Cu2H2– with CO2 at variable temperatures (∼300–560 K) was investigated. Metal hydrides are the ideal models to study the nature of C–H bond formation in CO2 hydrogenation, while the related studies are scarcely reported, particularly for the hydrogenation reactions at temperatures above 300 K. The generation of formate (HCO2–) attached on product CuH2CO2– was identified by temperature-dependent mass spectrometric experiments and density functional theory calculations. Temperature played crucial roles to fine-tune the product selectivity, from Cu2H2CO2– that dominates the room-temperature reaction into CuH2CO2– at elevated temperatures. The nature behind the temperature-dependent product selectivity and the mechanism of CO2 hydrogenation has been interpreted by using theoretical calculations. The combined experimental and computational studies have provided solid evidence for the formation of formate attached in CuH2CO2–.