Carbon dioxide mediated, reversible chemical hydrogen storage using a Pd nanocatalyst supported on mesoporous graphitic carbon nitride

Abstract

Reversible, carbon dioxide mediated chemical hydrogen storage was first demonstrated using a heterogeneous Pd catalyst supported on mesoporous graphitic carbon nitride (Pd/mpg-C₃N₄). The Pd nanoparticles were found to be uniformly dispersed onto mpg-C₃N₄ with an average size of 1.7 nm without any agglomeration and further exhibit superior activity for the dehydrogenation of formic acid with a turnover frequency of 144 h⁻¹ even in the absence of external bases at room temperature. Initial DFT studies suggest that basic sites located at the mpg-C₃N₄ support play synergetic roles in stabilizing reduced Pd nanoparticles without any surfactant as well as in initiating H₂-release by deprotonation of formic acid, and these potential interactions were further confirmed by X-ray absorption near edge structure (XANES). Along with dehydrogenation, Pd/mpg-C₃N₄ also proves to catalyze the regeneration of formic acid via CO₂ hydrogenation. The governing factors of CO₂ hydrogenation are further elucidated to increase the quantity of the desired formic acid with high selectivity.