Rapid release of 1.5 equivalents of hydrogen from CO2-treated ammonia borane

Abstract

This work addresses the accelerated dehydrogenation of ammonia borane (AB, NH3BH3) in two separate processes of CO2 pre-treatment of AB and dehydrogenation of the treated AB. Decouphng these two processes can still keep the dehydrogenation activity of CO2-treated AB and eliminate the purification step of H-2 from gas phase. When AB is exposed to 1.38 MPa of carbon dioxide (CO2) at 70 degrees C, it shows the most favorable and controllable operating condition for the CO2 pre-treatment. The pre-treatment enhances not only the rate but also the amount of hydrogen release at the dehydrogenation step; 1.5 mol H-2 per mol of AB rapidly desorbs at 85 degrees C in 1 h, corresponding to 10.1 wt.% of hydrogen with regard to pristine AB. Also, our observations show that the fast dehydrogenation resulted from the CO2 pre-treatment is preserved for more than four days of storage. The degree of dehydrogenation is further confirmed by ATR-FTIR spectroscopic and elemental analyses of the solid product. The spectra display the N-H stretching mode involving pi-bonded nitrogen (sp(2) N) at ca. 3434 cm(-1),while the atom ratio of H:B is found to be 2.84:1. Based on the hydrogen release measurements, spectroscopic observations and elemental analyses, we deduce that the predominant solid product of dehydrogenation of CO2-treated AB at 85 degrees C is a polymer with an empirical formula of (NBH3)(n). It corresponds to the solid product after 1.5 equivalent hydrogen release of AB. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.