Dehydrogenation characteristics of ammonia borane via boron-based catalysts (Co–B, Ni–B, Cu–B) under different hydrolysis conditions

Abstract

In the present study, dehydrogenation characteristics of ammonia borane (NH3BH3) catalyzed via boron-based catalysts under different hydrolysis conditions were investigated. A series of boron-based catalysts (Co1−x–Bx, Ni1−x–Bx, and Cu1−x–Bx, x: 0.25, 0.50, 0.75) were prepared by sol–gel method. Gels were calcinated at different temperatures (250 °C, 350 °C, and 450 °C) in order to obtain the boron-based catalysts. XRD characterizations revealed that Co–B, Ni–B, and Cu–B crystalline structures were formed during calcination at 450 °C. Hydrogen generation measurements were performed in order to determine the optimum composition of the boron-based catalyst. The maximum hydrogen generation rates were 7607 ml min−1 gcat−1, 3869 ml min−1 gcat−1 and 1178 ml min−1 gcat−1 for Co0.75B0.25, Ni0.75B0.25 and Cu0.75B0.25, respectively. Furthermore, the hydrolysis of NH3BH3 was performed at 20 °C, 40 °C, 60 °C and 80 °C under magnetic stirring (750 rpm), ultrasonic irradiation and non-stirring in order to determine how these parameters effect hydrolysis. Activation energies (Ea) were calculated by evaluation of the kinetic data. Under ultrasonic irradiation, the Ea in the presence of Co0.75B0.25, Ni0.75B0.25 and Cu0.75B0.25 were 40.85 kJ mol−1, 43.19 kJ mol−1 and 48.74 kJ mol−1, respectively, which compares favorably with results reported in the literature. Thus, the catalytic activities of the boron-based catalysts were found to be Cu < Ni < Co and the best reaction condition for the catalytic hydrolysis of NH3BH3 was determined to be non-stirring < magnetic stirring < ultrasonic irradiation.