PdIr nanoparticles on NH2-functionalized dendritic mesoporous silica nanospheres for efficient dehydrogenation of formic acid

Developing highly efficient solid catalysts for formic acid (HCOOH, FA) dehydrogenation is essential to utilize FA as a hydrogen (H2) carrier. In this work, ultrafine bimetallic PdIr nanoparticles (NPs) supported on the amine-functionalized dendritic mesoporous silica nanospheres (PdIr/DMSNs-NH2) have been successfully synthesized by the simple surface functionalization and co-reduction method. The optimized Pd4Ir1/DMSNs-NH2 (Pd/Ir molar ratio = 4:1) catalyst displayed the remarkable catalytic performance with 100 % H2 selectivity of the FA dehydrogenation, and the initial turnover frequency (TOF) could achieve 1333 h−1 with the additive of sodium formate (SF) at 298 K, which is comparable to the most effective mesoporous silica supported Pd-containing solid catalysts. The activation energy (Ea) for the FA dehydrogenation of Pd4Ir1/DMSNs-NH2 catalyst in the FA-SF mixture is 39.7 KJ/mol, lower than most reported catalysts. Furthermore, the optimized catalyst maintained 100 % H2 selectivity even after five runs, only with a negligible decrease in the activity, displaying the excellent stability of the catalyst. The superior catalytic performance could be attributed to the synergistic effect of open dendritic pore channel, high dispersion and ultrafine size of PdIr NPs as the active sites on DMSNs-NH2, and regulated electronic effects of Pd and Ir. More importantly, introducing –NH2 groups to the DMSNs could facilitate the O–H bond dissociation of FA and improve the FA dehydrogenation activity under mild conditions. This work will significantly promote FA as a hydrogen carrier on fuel cells.