Reaction mechanism and kinetics for hydrolytic dehydrogenation of ammonia borane on a Pt/CNT catalyst

A reaction mechanism is proposed for hydrolytic dehydrogenation of ammonia borane on a Pt/CNT catalyst. A combination of thermodynamic analysis and FTIR measurement reveals that B‐containing byproducts are mainly in the form of an NH 4 B(OH) 4 ‐B(OH) 3 mixture rather than NH 4 BO 2 reported previously. The revised main reaction isNH 3BH 3 + 4 H 2 O → NH 4 + + B( OH ) 4 − + 3 H 2 ↑ , involving the B–H, B–N, and O–H bond cleavages. Isotopic experiments using D 2 O instead of H 2 O as reactant or introducing D 2 into the reaction atmosphere suggest the O–H bond cleavage being in the rate‐determining step, and an unfavorable occurrence of the chemisorbed H 2 O dissociation (i.e., the direct O–H bond cleavage), respectively. Different reaction pathways with indirect O–H bond cleavages are analyzed, and thenNH 3BH 2 * + H 2 O * → NH 3BH 2( OH ) * + H *is suggested as the rate‐determining step. Subsequently, a Langmuir–Hinshelwood kinetic model is developed, which fits well with the experimental data. © 2016 American Institute of Chemical Engineers AIChE J , 63: 60–65, 2017