Stick-like mesoporous titania loaded Pd as highly active and cost effective catalysts for hydrodebenzylation of hexabenzylhexaazaisowurtzitane (HBIW)

Abstract

Hydrodebenzylation of hexabenzylhexaazaisowurtzitane (HBIW) is one key step for the synthesis of High Energy Density Compound CL-20 (hexanitrohexaazaisowurtzitane). Design of a “high atom economy” debenzylation catalyst to promote the industry production and massive use in the fields of aerospace and military has attracted great attentions. Herein, we designed a catalyst of stick-like mesoporous titania supported ultrafine Pd nanoparticles with low loading 2 wt.% using a hydrothermal and then deposition-precipitation method. The supports and catalysts were thoroughly characterized by N2 physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Raman, ultraviolet–visible absorption (UV–vis), in situ diffuse reflectance infrared Fourier transform (DRIFT), H2 chemisorption to determine their physical and chemical properties. The results revealed that stick-like titania (ST) treated at low temperature showed rutile crystalline structure, large interplanar spacing (3.2394 Å) and surface area (53 m2/g), small average crystallite size (63 nm) with mesoporous. The Pd can deposit into the interstices and lattice of ST and displayed ultrafine and even sub-nanometer sizes (average value 1.2 nm), and high dispersion. The Pd/ST-2 exhibited particularly high activity for hydrodebenzylation of HBIW. The product TADBIW was obtained in a high turnover number (TON) 107, which is 2 ˜ 5 times higher than those of conventional Pd/C catalysts. This work paves a promising way to develop highly efficient catalysts with low loading of Pd and high atomic utilization for cost-effective synthesis of CL-20.