Facile fabrication of poly(amidoamine) (PAMAM) dendrimers-encapsulated Ag–Co bimetallic nanoparticles for highly efficient dehydrogenation of ammonia borane

Abstract

Multifunctional poly(amidoamine) (PAMAM) dendrimers-encapsulated Ag–Co bimetallic nanoparticles (Ag–Co/PAMAM NPs) have been prepared via a facile co-complexation chemical reduction method. By exploiting the well-defined dendritic spatial construction of PAMAM dendrimers as NPs support and capping ligand, the as-synthesized NPs show unconspicuous agglomeration and uniformly distribution with average diameter of 5 nm. The Ag–Co/PAMAM NPs show the composition-dependent catalytic activity in catalytic dehydrogenation of ammonia borane (AB), with NPs in 30 atom.% Ag exhibiting the superior activity and yielding an initial turnover frequency (TOF) as high as 15.84 molH2·min−1·molM−1. Combined with the electro–transfer interaction between Ag and Co, the effective control of the NPs dispersibility and the electro-donating ability of PAMAM dendrimers with amounts of amide and amine groups facilitate the catalytic performances of Ag–Co/PAMAM catalyst on the hydrolysis of AB. The work also includes the kinetic studies on zero-order with respect to substrate concentration and first-order reaction with respect to catalyst concentration, as well as temperature effect to determine the apparent activation energy of the reaction (Ea = 35.66 kJ mol−1). Furthermore, the reusability tests reveal Ag–Co/PAMAM NPs still show good catalytic activity and magnetically reusability in successive runs, which make these dendrimers-stabilized bimetallic nanoparticles promising heterogeneous catalysts in practical application.