Ammonia borane-based reactive mixture for trapping and converting carbon dioxide

Abstract

Ammonia borane (NH₃BH₃) is a reducing agent, able to trap and convert carbon dioxide. In the present work, we used a reactive solid consisting of a mixture of 90 wt.% of NH₃BH₃ and 10 wt.% of palladium chloride, because the mixture reacts in a fast and exothermic way while releasing H₂ and generating catalytic Pd⁰. We took advantage of such reactivity to trap and convert CO₂ (7 bar), knowing besides that Pd⁰ is a CO₂ hydrogenation catalyst. The operation (i.e. stage 1) was effective: BNH polymers, and B—O, C=O, C—O, and C—H bonds (like in BOCH₃ and BOOCH groups) were identified. We then (in stage 2) pyrolyzed the as-obtained solid at 1250 °C and washed it with water. In doing so, we isolated cyclotriboric acid H₃B₃O₆ (stemming from B₂O₃ formed at 1250 °C), hexagonal boron nitride, and graphitic carbon. In conclusion, the stage 1 showed that CO₂ can be ‘trapped’ and converted, resulting in the formation of BOCH₃ and BOOCH groups (possible sources of methanol and formic acid), and the stage 2 showed that CO₂ transforms into graphitic carbon.