Abstract
In the present work we studied the effect of cobalt halides (CoF 2, CoCl 2, CoBr 2 and CoI 2; also denoted CoX 2) on the thermal decomposition of ammonia borane NH 3BH 3 (AB) over the range 25–220 °C. The reaction was followed by thermogravimetric analysis and differential scanning calorimetry. The gaseous products analyzed by gas chromatography and mass spectrometry, and the solid by-products identified by elemental analysis: powder X-ray diffraction, infrared and X-ray photoelectron spectroscopies. Compared to pristine AB, the presence of CoCl 2 and CoBr 2 reduces both the induction period of the AB decomposition and the content of unwanted borazine in the H 2 stream, whereas the presence of CoI 2 or CoF 2 has little or no effect, respectively. We propose that the positive effect of CoX 2 comes from their electronic and steric effects, and that CoCl 2 is the compound which shows the best properties relative to these effects. Herein, the roles of Co and X are discussed and a revised mechanism of the AB dehydrocoupling initiation is proposed.
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