Investigation of the reaction mechanism and conditions in ammonia borane alcoholysis with different alcohols (CH3OH, CH3CH2OH, and (CH2OH)2)

Abstract

In the study, ammonia borane alcoholysis with different types of alcohols (CH₃OH, CH₃CH₂OH, and (CH₂OH)₂) for hydrogen production is investigated, and the effects of different pressures and temperatures on the adsorption properties are also investigated using DFT calculations and experimental methods. In ammonia borane alcoholysis, NH₃BH₃ molecules and alcohol molecules (R–OH) are first adsorbed onto the active metal surface, where the hydroxyl groups in the R–OH molecules are activated and the O–H bonds are broken to produce the intermediates H* and *O–R. Furthermore, a strong interaction between the B in NH₃BH₃ and the O in *O–R occurs and the B–N bond is broken, forming the intermediate products *NH₃, *BH₂–O–R and another H*; the H₂ molecule is released during B–O bonding with one of the H originating from the hydroxyl group and the other originating from the *HB in the NH₃BH₃ molecule. The energy barriers for the ammonia borane alcoholysis with CH₃OH, CH₃CH₂OH and (CH₂OH)₂ are 28.23 kcal mol⁻¹, 37.5 kcal mol⁻¹ and 42.32 kcal mol⁻¹, respectively, which result in a different alcoholysis rate of ammonia borane AB/CH₃OH > AB/CH₃CH₂OH > AB/(CH₂OH)₂ at the macroscopic level. The high pressure enhances the adsorption properties of ammonia borane and alcohol molecules, while the high temperature decreases the adsorption properties. The adsorption capacities of ammonia borane and alcohols on the active metal Ru (101) are CH₃OH (0.32 mmol g⁻¹) < NH₃BH₃ (1.03 mmol g⁻¹) < CH₃CH₂OH (1.05 mmol g⁻¹) < (CH₂OH)₂ (1.31 mmol g⁻¹) specifically. The results of this study provide a theoretical basis for the regulation of hydrogen production from ammonia borane alcoholysis.