Hydroxyl-mediated palladium single-atom catalyst for highly efficient hydrogen storage

Hydrogen storage in liquid organic hydrogen carriers (LOHCs) is regarded as one of the most promising strategies and efficient hydrogen storage. However, the development of highly efficient dehydrogenation catalysts remains a significant challenge. This study investigated the synergistic effect of surface-bound hydroxyl (-OH) groups and palladium single-atom on mesoporous silica (MCM-41) catalyst in the dehydrogenation of dodecahydro-N-ethylcarbazole (12H-NEC). The optimized catalyst achieved complete dehydrogenation of 12H-NEC under low-temperature of 175 °C, demonstrating a dehydrogenation rate of 99.7 % (100 % conversion at 0.5 wt% Pd loading), while MCM-41 with fewer hydroxyl groups exhibited a much lower dehydrogenation rate of only 46 % under the same conditions. Systematic optimization of surface hydroxyl content enabled atomic-level dispersion of Pd, as confirmed by X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) analysis, which revealed stable Pd-O coordination structures without detectable Pd clusters. Kinetic studies demonstrate a stepwise dehydrogenation mechanism where the 4H-NEC dehydrogenation step constitutes the rate-determining process. Density functional theory (DFT) calculations further elucidate that Pd single atoms significantly reduce intermediate adsorption energies compared to metallic clusters, thereby accelerating hydrogen release. These findings provide critical insights for designing low-loading, single-atom catalysts optimized for efficient dehydrogenation applications.