Zeolite-Encaged Pd-Mn Nanocatalysts for CO2 Hydrogenation and Formic Acid Dehydrogenation

Abstract

A CO₂ -mediated hydrogen storage energy cycle is a promising way to implement a hydrogen economy, but the exploration of efficient catalysts to achieve this process remains challenging. Herein, sub-nanometer Pd-Mn clusters were encaged within silicalite-1 (S-1) zeolites by a ligand-protected method under direct hydrothermal conditions. The obtained zeolite-encaged metallic nanocatalysts exhibited extraordinary catalytic activity and durability in both CO₂ hydrogenation into formate and formic acid (FA) dehydrogenation back to CO₂ and hydrogen. Thanks to the formation of ultrasmall metal clusters and the synergic effect of bimetallic components, the PdMn_0.6 @S-1 catalyst afforded a formate generation rate of 2151 mol_formate mol_Pd ^-1 h^-1 at 353 K, and an initial turnover frequency of 6860 mol ${}_{H{}_2}$ mol_Pd ^-1 h^-1 for CO-free FA decomposition at 333 K without any additive. Both values represent the top levels among state-of-the-art heterogeneous catalysts under similar conditions. This work demonstrates that zeolite-encaged metallic catalysts hold great promise to realize CO₂ -mediated hydrogen energy cycles in the future that feature fast charge and release kinetics.

Keywords: CO2 hydrogenation; formic acid; heterogeneous catalysis; hydrogen storage; zeolites.