Catalytic hydrolysis of ammonia borane: Intrinsic parameter estimation and validation

摘要

Ammonia borane (AB) hydrolysis is a potential process for on-board hydrogen generation. This paper presents isothermal hydrogen release rate measurements of dilute AB (1 wt%) hydrolysis in the presence of carbon supported ruthenium catalyst (Ru/C). The ranges of investigated catalyst particle sizes and temperature were 20-181 μm and 26-56℃, respectively. The obtained rate data included both kinetic and diffusion-controlled regimes, where the latter was evaluated using the catalyst effectiveness approach. A Langmuir-Hinshelwood kinetic model was adopted to interpret the data, with intrinsic kinetic and diffusion parameters determined by a nonlinear fitting algorithm. The AB hydrolysis was found to have an activation energy 60.4 kJ mol~(-1), pre-exponential factor 1.36×10~(10)mol(kg-cat)~(-1) s~(-1), adsorption energy -32.5 kJ mol~(-1), and effective mass diffusion coefficient 2 ×10~(-10) m~2 s~(-1). These parameters, obtained under dilute AB conditions, were validated by comparing measurements with simulations of AB consumption rates during the hydrolysis of concentrated AB solutions (5-20 wt%), and also with the axial temperature distribution in a 0.5 kW continuous-flow packed-bed reactor.