Catalytic hydrolysis of ammonia borane: Intrinsic parameter estimation and validation

Abstract

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 °C, 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.