Unlocking Improved Formic Acid Dehydrogenation of Pd Nanoparticles Immobilized on Amine-Functionalized Yolk–Shell Silica

In this work, a series of mesoporous yolk-shell silica spheres (YS-<i>x</i>) with tunable yolk size and shell thickness were synthesized via the incubation method in water. Following amination and Pd loading treatment on YS-<i>x</i>, a series of catalysts Pd-YS-<i>x</i>-NH₂ were obtained successfully and applied to formic acid (FA) dehydrogenation for hydrogen (H₂) generation. The optimal catalyst Pd-YS-6-NH₂, which has an appropriate yolk size and shell thickness, the largest specific surface area, and pore volume, as well as the smallest Pd nanoparticles (NPs), exhibits dehydrogenation performance far superior to that of other reference catalysts. It shows an extraordinary turnover frequency (TOF, 4508 h^-1) and excellent stability at 60 °C with sodium formate (SF). After five testing cycles, it still maintained 100% FA conversion, and the decline in catalytic performance is almost negligible. The excellent catalytic performance of Pd-YS-6-NH₂ is attributed to the optimal yolk-shell structure, the introduction of amine groups, and highly dispersed and ultrasmall Pd NPs (1.5 nm). This study provides methods for yolk-shell catalyst design and development for FA dehydrogenation.