Catalytic Aspects in the Synthesis of a Promising Energetic Material

Synthesis of a promising energetic material CL-20 requires the two-step catalytic re-functionalization of N-bonded benzyl groups (CH2-C6H5) of hexabenzylhexaazaisowurtzitane (HBIW) into acetyl (-CO-CH3) or formyl groups (-CHO) over Pd/C catalyst before its direct nitrolysis into final CL-20 product. Utilization of an expensive palladium-based catalyst deactivated fast during reaction contributes substantially to a high CL-20 cost being a significant hurdle limiting wide application of CL-20 in a propellant formulation. In this work a careful systematic study was performed to improve efficiency, resistance to deactivation, and life-time of Pd/C catalysts as well as to elucidate the optimal hydrodebenzylation reaction conditions. The catalyst activity decrease for Pd/C was found to be caused mainly by agglomeration of metal nanoparticles, Pd re-deposition on inaccessible inner areas of the carbon support, and blocking of the metallic palladium with by-products of intermediates destruction. Different ways to enhance Pd/C catalytic activity through an improvement of Pd dispersion and resistance of Pd particles to agglomeration and re-oxidation as well as through an increase of Pd accessibility for large HBIW molecules were proposed. The two-step HBIW debenzylation with a separately repeated use of the catalyst in each catalytic stage was considered as a promising way to increase catalyst productivity and to diminish CL-20 production costs.