Kinetics of Hydrogen Evolution during Amminborane Hydrolysis with Cobalt-Based Catalysts

Abstract

The kinetics of hydrogen evolution during the hydrolysis reaction of aqueous solutions of amminborane with cobalt-based catalysts deposited on various substrates – Co3O4/ZnO, Co/ZnO, Co3O4/zeolite, Co/zeolite, as well as Co(OH)2 powder, was studied. In each case, the reaction order, the rate constants and apparent activation energy of the reaction, and the rate of hydrogen evolution during hydrolysis in the temperature range 35–80°C were determined. In all cases, an amminborane solution with a concentration of 0.078 M was used. The amount of the active part of the catalysts was determined by the chemical method and was 7.5–10% of the total weight of the catalyst. For low-temperature Co–B and Co(OH)2 catalysts, the kinetic dependences corresponded to the zero or close to zero reaction order. When using the catalysts Co3O4/ZnO, Co/ZnO, Co3O4/zeolite, Co/zeolite, the first order of the reaction was observed. The maximum rate of hydrogen evolution at 80°C was 3125 mL H2 · (g-cat–1) · min–1 for Co/ZnO catalyst (turnover frequency TOF = 8.2 min–1) and 3750 mL H2 · (g-cat–1) · min–1 for Co–B catalyst (TOF = 11.7 min–1), respectively. The values of the apparent activation energy of the reaction of catalytic hydrolysis of amminborane were calculated for the catalysts: Co3O4/ZnO – 26.0, LT Co–B – 44.8, Co(OH)2 black – 43.4, Co(OH)2 blue – 47.4 kJ/mol, respectively.