An Effective Strategy to Boost Formic Acid Dehydrogenation over Pd/AC-NH₂ Catalyst through Pd Size Control

Formic acid (FA, HCOOH) is regarded as one of the most promising carriers for hydrogen storage. However, the catalyst design for FA dehydrogenation into H₂ with high efficiency is not clear. Here, we elucidate the rationale of size effect over the most commonly used Pd-based catalyst through supporting different Pd species, including single atoms, nanoclusters, and nanoparticles, on amine-functionalized active carbon (Pd/AC-NH₂). The activity test presents that Pd/AC-NH₂ with Pd nanoclusters exhibits the best turnover frequency (TOF) value of 40856 h^-1 for 1 M FA at 328 K and even 1504 h^-1 for neat FA at 308 K, which is comparable to the homogeneous catalysts and has been the first heterogeneous catalyst used in neat FA dehydrogenation under mild conditions. The comprehensive characterizations reveal that the size of Pd species affects the ratios of Pd⁰/Pd²⁺ and hydrogen spillover effect, which is crucial for the C-H cleavage and H₂ desorption. Besides, the influences of amine groups on catalytic performance were further examined. This work provided an ingenious guideline to design efficient and practical catalysts for hydrogen storage under ambient conditions.