Interfacial Engineering of PdAg/TiO<sub>2</sub> with a Metal–Organic Framework to Promote the Hydrogenation of CO<sub>2</sub> to Formic Acid
Kohsuke Mori, Atsushi Konishi, Hiromi Yamashita
Abstract
The interfacial postmodification of PdAg alloy nanoparticles (NPs) supported on TiO2 was performed, using the widely studied metal–organic framework ZIF-8. The resulting PdAg/TiO2@ZIF-8 enhanced the selective hydrogenation of CO2 to give formic acid (FA) even under relatively mild reaction conditions (2.0 MPa, 100 °C). The highest activity, which was almost double the value obtained from the unmodified catalyst, was obtained with about 1.6 nm-thick ZIF-8 layer. Density functional theory calculations show that the presence of the ZIF-8 framework on the PdAg(111) surface not only enhances the adsorption of HCO3– ions but also promotes electronic interactions between the C atoms of HCO3– ions and also changes the atomic charge of C atoms of adsorbed HCO3– ions, based on the vertical orientation of the 2-methylimidazole rings, which promotes electronic interactions with dissociated H atoms. This interfacial postmodification also increases the durability of the catalyst by suppressing the agglomeration of NPs during the catalytic reaction.