Supported Core–Shell Alloy Nanoparticle Catalysts for the Carbon Dioxide Hydrogenation to Formic Acid

Abstract

The hydrogenation of carbon dioxide (CO₂) to formic acid (FA; HCOOH), a renewable hydrogen storage material, is a promising approach to realize to address climate change since the target product is valuable as commodity chemicals as well as a renewable hydrogen storage material. Unfortunately, the development of heterogeneous catalysts lags significantly over the homogeneous catalysts in spite of the obvious practical advantages of such materials. Herein, the state of the art in the exploitation of promising metal alloy nanoparticle catalysts designed by surface engineering with atomic precision for this targeted reaction is presented. Especially, isolated and electron-rich Pd atoms created with the aid of neighboring Ag atoms in Pd@Ag alloy NPs boost the electronegativity of the dissociated hydride species, which exhibit ten times higher activity than those provided by monometallic Pd/TiO₂ based on equivalent quantities of surface Pd atoms. Moreover, the post-modification of PdAg alloy NPs supported on TiO₂ was performed using metal–organic framework ZIF-8. The observed increase in catalytic activity is ascribed to the positive electronic effects on both the active metal centers and reactants, as well as an anchoring stabilization effect preventing the undesired agglomeration of NPs during the reaction. Furthermore, core–shell structured catalyst (ZIF-8@Pd₁Ag₂@ZIF-8) was developed by the encapsulation of PdAg NPs within the interface of ZIF-8.