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

Abstract

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 NH4B(OH)4‐B(OH)3 mixture rather than NH4BO2 reported previously. The revised main reaction is , involving the B–H, B–N, and O–H bond cleavages. Isotopic experiments using D2O instead of H2O as reactant or introducing D2 into the reaction atmosphere suggest the O–H bond cleavage being in the rate‐determining step, and an unfavorable occurrence of the chemisorbed H2O dissociation (i.e., the direct O–H bond cleavage), respectively. Different reaction pathways with indirect O–H bond cleavages are analyzed, and then 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

“Click” Dendrimer‐Stabilized Nanocatalysts for Efficient Hydrogen Release upon Ammonia‐Borane Hydrolysis

“…Another useful tool towards mechanistic investigation is the isotopic experiment using D 2 O instead of H 2 O that has already been probed in several articles . The kinetic results are shown in Figure for RhNPs and PtNPs.…”

“…Recently, non‐noble metal NPs have also been reported as catalysts, although much less efficient than their noble metal analogues . The reaction was initially shown to produce ammonium borate NH 4 + BO 2 − , but the groups of Duan and DeChen recently reported kinetic and mechanistic studies showing that the reaction in fact produces NH 4 + B(OH) 4 − …”

“…[7] The reactionw as initially shown to produce ammoniumb orate NH 4 + BO 2 À ,b ut the groups of Duan and DeChen recently reported kinetic and mechanistics tudies showing that the reaction in fact produces NH 4 + B(OH) 4 À . [8] Here we report comparative studies among late transition metal NPs including noblem etal and non-noble metal NPs [9] stabilized by "click" dendrimers [10] allowing the optimization of the choice of the metal.W ea lso examine the influence of NaOH [6b, 7f,11] on the reactione fficiency of the most efficient NP catalysts and find that this influence is positive or negative depending on the metals. Isotopic experiments using D 2 Oinstead of H 2 Oa re also disclosed with mechanistic conclusion concerning bond cleavage in the transition step.…”

Facile Synthesis of Three‐Dimensional Pt‐TiO2 Nano‐networks: A Highly Active Catalyst for the Hydrolytic Dehydrogenation of Ammonia–Borane

“…[22] (1)] is the most efficient way of releasing hydrogen from AB,which is mainly due to favorable kinetics under mild conditions.…”

Facile Synthesis of Three‐Dimensional Pt‐TiO2 Nano‐networks: A Highly Active Catalyst for the Hydrolytic Dehydrogenation of Ammonia–Borane

“…(1)] is the most efficient way of releasing hydrogen from AB,which is mainly due to favorable kinetics under mild conditions. [22] H 3 Since the reaction is required to be catalyzed at an appreciable rate at ambient temperature,developing efficient and stable catalysts for hydrogen generation from AB is ac hallenge for fuel cell applications.A lthough various supported transition metal nanoparticles have been tested for H 2 generation from the hydrolysis of ammonia-borane, [23] Pt has been shown to be the superior catalyst. [21,24] However, high price and low abundance of Pt in the Earth crust limit its catalytic application.…”