In order to achieve an economical CO2-mediated hydrogen energy cycle, the hydrogenation of carbon dioxide (CO2) to formic acid (FA; HCOOH), a renewable hydrogen storage material, is a promising strategy. Using this compound, chemically stored hydrogen could be liberated in a controlled manner in the presence of appropriate catalysts, even at room temperature. Significant efforts have been devoted to the research of homogeneous transition metal complexes as catalysts for FA production, especially those based on Ir and Ru, and interesting results have been obtained. The development of reliable heterogeneous catalysts is an urgent yet challenging task, although their use frequently requires a high catalyst concentration, organic solvents, and extremely high pressures. and, to make matters worse, precise catalytic site design protocols are still lacking. A stable and well-defined single-atom Ru catalyst on the surface of a layered double hydroxide (LDH) has been developed as a selective heterogeneous catalyst for the hydrogenation of CO2 to FA under mild reaction conditions. The electron-donating ability of triads of basic hydroxyl ligands with a particular location is crucial for an active electron-rich Ru center. There is a strong correlation between catalytic activity and adjustable CO2 adsorption capacity in the vicinity of the Ru center (Figure 1A). We also demonstrate that PdAg alloy nanoparticles supported on TiO2 efficiently promote the hydrogenation of CO2 to give FA. Specimens made using surface engineering with atomic precision reveal a strong correlation between increased catalytic activity and decreased electron density of active Pd atoms resulting from a synergistic effect of alloying with Ag atoms (Figure 1B). The isolated and electronically promoted surface-exposed Pd atoms in Pd@Ag alloy NPs exhibit a maximum turnover number of 14,839 based on the quantity of surface Pd atoms. Possible reaction pathways proposed upon consideration of kinetic and DFT calculations were also discussed.

Design of nanostructured heterogeneous metal catalysts for CO2 hydrogenation to formic acid

2019 Fall National Meeting

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