Hydrogen Production via Cerium-Promoted Dehydrogenation of Formic Acid Catalyzed by Carbon-Supported Palladium Nanoparticles

Formic acid is a promising hydrogen carrier owing to its high hydrogen density and liquid phase. Therefore, the production of hydrogen from formic acid via catalytic dehydrogenation reaction has been extensively studied. Various methods such as alloying of the active Pd metal with other metals and adding dopants (e.g., the amine-functional group, nitrogen, or metal oxide) have been suggested to enhance the catalytic activities for formic acid dehydrogenation. In this study, we synthesized carbon-supported palladium nanoparticles coexisting with ceria particles and investigated the role of cerium in this reaction over Pd/C catalysts. We made an effort not to change the particle size and the electronic state of Pd significantly while varying Ceria/Pd molar ratios in the catalysts, ruling out their effects on the reaction. Ceria was impregnated on carbon by incipient wetness impregnation; subsequently, Pd was impregnated on Ceria/C by deposition–precipitation. The catalytic tests demonstrated that ceria improved the reaction rate by producing formate anions, the main reactant of this reaction, as it was dissolved by formic acid during the reaction. More importantly, the dissolved cerium ions accelerated the reaction by interacting with the formate anion to change its electronic charge, thereby reducing the activation barrier for C–H bond cleavage. The carbon-supported palladium nanoparticles promoted by cerium could be used to develop a highly efficient hydrogen extraction system from formic acid.