| Abstrakt: |
We investigate the kinetics of hydrogen evolution during the hydrolysis reaction of aqueous solutions of ammonia borane with cobalt-based catalysts deposited onto various substrates (Co3O4/ZnO, Co/ZnO, Co3O4/zeolite, and Co/zeolite) and in the form of Co(OH)2 powder. In each case, we determine the reaction order, rate constants, the apparent activation energy of the reaction, and the rate of hydrogen evolution during hydrolysis in the temperature range of 35–80°С. A solution of ammonia borane with a concentration of 0.078 M is used in all cases. The amount of the active part of the catalysts is determined by the chemical method; it is 7.5–10% of the total catalyst weight. For the low-temperature Co–B catalyst and Co(OH)2, the kinetic dependences correspond to the zero or close-to-zero order of the reaction. The Co3O4/ZnO, Co/ZnO, Co3O4/zeolite, and Co/zeolite catalysts ensure the first order of the reaction. The maximum rate of hydrogen evolution at 80°С is 3125 mL H2 (g cat)–1 min–1 for Co/ZnO (turnover frequency is TOF = 8.2 min–1) and 3750 mL H2 (g cat)–1 min–1 (TOF = 11.7 min–1), respectively. The apparent activation energy of the reaction of the catalytic hydrolysis of ammonia borane is calculated as 26.0 kJ/mol for Co3O4/ZnO, 44.8 kJ/mol for Co–B, 43.4 kJ/mol for black Co(OH)2, and 47.4 kJ/mol for blue Co(OH)2. [ABSTRACT FROM AUTHOR] |
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