PdAg Nanoparticles Supported on Functionalized Mesoporous Carbon: Promotional Effect of Surface Amine Groups in Reversible Hydrogen Delivery/Storage Mediated by Formic Acid/CO2

Highly dispersed PdAg nanoparticles supported on phenylamine-functionalized mesoporous carbon were synthesized and assessed as bifunctional heterogeneous catalysts for the interconversion of formic acid (FA) and CO2 in chemical hydrogen storage systems. A high turnover frequency (TOF) of 5638 h–1 for evolved H2 on the basis of the total amount of Pd in the sample was obtained during the dehydrogenation of FA, corresponding to a TOF value of 21686 h–1 on the basis of the quantity of surface Pd atoms. In addition, this material promoted the hydrogenation of CO2 to FA with a turnover number (TON) of 839 over 24 h for produced FA on the basis of the total amount of Pd, corresponding to a TON of 3227 on the basis of the quantity of surface Pd atoms. Both the synergistic alloying effect and the surface functionalization with weakly basic phenylamine molecules were vital aspects of these high catalytic activities. Experimental and theoretical studies revealed that the cooperative action of the phenylamine groups in the vicinity of active PdAg NPs significantly affected the O–H dissociation of FA as well as the CO2 adsorption capacity of the catalyst, which ultimately boosted the catalytic activity for both reactions. This work also represents a demonstration of a catalyst that promotes the reversible interconversion between FA and CO2 under heterogeneous conditions and is recyclable for at least three cycles without loss of activity. Additionally, the present catalyst performs well even in flow chemistry experiments using a fixed-bed reactor, indicating the potential for various industrial applications.