Study on catalytic activity and mechanism of tetrazole-based energetic metal-organic frameworks for thermal decomposition of ammonium perchlorate

In order to comprehensively improve the energy performance and combustion properties of the propellants, four energetic metal–organic frameworks (EMOFs) constructed from transition-metal ions (Ag⁺, Cd²⁺, Pb²⁺) and tetrazole-based energetic ligands (5-methyl tetrazole (HMtta), N,N-bis(1H-tetrazole-5-yl)-amine (H₂bta), 3-(1H-tetrazol-5-yl)-1H-triazole (H₂tztr)) were prepared by hydrothermal synthesis. The crystal phase and structure of the as-prepared samples were analyzed by XRD and IR characterization. Their catalytic activity on thermal decomposition of ammonium perchlorate (AP) was evaluated by DSC. The results show that as-prepared EMOFs can significantly reduce the thermal decomposition temperature of AP and increase its heat release. Under the optimal condition that the addition amount is 10 wt%, the high-temperature decomposition peak temperatures of [AgMtta]_n/AP, [Cd₅(Mtta)₉]_n/AP, [Pb₃(bta)₂(O)₂(H₂O)]_n/AP, and [Pb(Htztr)₂(H₂O)]_n/AP are decreased by 107.2°C, 94.2°C, 54.6°C, and 91.1°C compared to the case of pure AP, while the heat releases of them are increased by 1243.9 J∙g⁻¹, 1226.2 J∙g⁻¹, 1332.2 J∙g⁻¹, 1444.4 J∙g⁻¹, respectively. In addition, compared with the reported catalysts such as [Pb(BTF)(H₂O)₂]_n, CuFe₂O₄, [Cu₂(en)₂(HBTI)₂]₂, and [Cu₂(en)(HBTI)₂]₂en, the EMOFs prepared in this study show equal or even higher catalytic activity and heat release. Moreover, the catalytic mechanism of EMOFs on thermal decomposition of AP is also analyzed based on the electron transfer theory. With the excellent energy properties and catalytic performances, the prepared EMOFs may become promising energetic additives for composite solid propellant applications.