Enhanced Formic Acid Dehydrogenation over Basic Site-Rich Pd/Al₂O₃ Hollow Sphere Catalyst

Formic acid (FA) is regarded as a safe and practical hydrogen carrier owing to its favorable storage and handling characteristics. However, achieving efficient and selective FA dehydrogenation under mild conditions remains a significant challenge. In this study, the decomposition pathway of FA was found to be highly dependent on the acid-base characteristics of the catalyst support, with basic surfaces preferentially favoring the dehydrogenation route. Therefore, a morphology-regulated strategy was developed to modulate the distribution of basic sites on alumina, revealing a direct structure-function relationship that governs the catalytic behavior. Al₂O₃ hollow spheres (HS), featuring abundant surface basicity, were synthesized via a hydrothermal method and used as supports for Pd catalysts alongside Al₂O₃ nanobelts (NB) and nanoparticles (NP). Mechanistic studies integrating catalytic evaluation, in situ DRIFTS, and CO₂-TPD analyses demonstrated that the Pd/Al₂O₃-HS catalyst, owing to its support enriched in basic sites, simultaneously facilitates formate formation and promotes the generation of the Pd-HCOO* intermediate, thereby enhancing H₂ production. This synergy results in superior catalytic performance (TOF = 4606 h^-1) with no detectable CO formation. The increased basicity of the support markedly improved the hydrogen evolution during formic acid decomposition, highlighting a strong correlation between support basicity and catalytic efficiency.