Abstract
A complex-reduction method was used for the synthesis of glycine-capped copper nanoparticles (Gly-CuNPs). Glycine-Cu2+ was prepared at room temperature, and the resulting complex was treated with NaBH4. Gly-Cu/Ag and Gly-Cu/Ag/MnO2 were prepared by using the stepwise metal displacement plating method. Gly-Cu, Gly-Cu/Ag and Gly-Cu/Ag/MnO2 were employed as catalysts for hydrogen generation from the decomposition of formic acid. The alkaline barium hydroxide solution was employed to trap CO2 formation, and pseudo-first-order rate constants were calculated by using the kobs = 2.303/t log(Aα-A0/Aα-At) relation. Hydrogen generation followed fractional order kinetics with formic acid, and various kinetic parameters were calculated for various concentrations of promoter (sodium format), catalyst and temperature. The catalytic activity was found to increase with an increasing number of incorporated metals, and the order of reactivity was as follows: Gly-Cu/Ag/MnO2 > Gly-Cu/Ag > Gly-Cu. For Gly-Cu/Ag/MnO2, the values of activation parameters (Ea = 56 kJ/mol, ∆H# = 53 kJ/mol, ∆S# = − 68 J/K/mol) were determined with the Arrhenius and Eyring equations, which show higher catalytic efficiency than that of Gly-Cu/Ag (Ea = 69 kJ/mol, ∆H# = 66 kJ/mol, ∆S# = − 25 J/K/mol) due to the synergistic effect and strong interactions between the three metals. The catalytic stability and recyclability were excellent for five consecutive cycles, but the stability and recyclability decreased due to the higher reactivity of MnO2 NPs.
•Glycine capped Cu, Cu/Ag and Cu/Ag/MnO2 prepared using complex and metal displacement reaction.•Hydrogen generation from formic acid decomposition depends on the nature of the catalyst.•Catalytic activity enhanced significantly with incorporating the silver and MnO2.•Glycine-Cu/Ag/MnO2 exhibits higher catalytic efficiency due to the synergistic effect.