Regulation of precipitation order on the physical–chemical properties of MgCo2Oz catalyst for AP thermal decomposition: catalytic performance and mechanism

Herein, two different precipitation sequences were proposed to fabricate layered Co/Mg hydroxide catalyst (Denoted as MgCo 2 O z ) in order to regulate the catalytic performance for ammonium perchlorate (AP) thermal decomposition. The results demonstrated that the change of precipitation sequence markedly altered the morphology, crystallinity, pore structure, and surface chemical states of the as-fabricated layered Co/Mg hydroxide catalysts. Compared with the as-synthesized MC-NH 3 ·H 2 O catalyst by dropping metal precursor solution into precipitating agent, MC-NH 3 ·H 2 O* synthesized by the opposite titration sequence produced greater reductions in the high-temperature decomposition temperature and apparent activation energy of AP, reaching 156.4 °C and 32.4 kJ mol −1 , respectively. And MC-NH 3 ·H 2 O* exhibited a microflower-like morphology, higher crystallinity, more abundant interlayer ionic species, and a higher average oxidation state of surface Co than MC-NH 3 ·H 2 O. Furthermore, the formed MgCo 2 O 4 -related or other Co/Mg mixed-oxide species from Co/Mg hydroxide precursor during heating up also played important role on AP catalytic thermal decomposition. Kinetic analysis indicated that AP/MC-NH 3 ·H 2 O and AP/MC-NH 3 ·H 2 O* composites generally exhibited nucleation-and-growth characteristics, with the dominant mechanism evolving from an L2-like random-fragmentation mode at low conversion to F2- and F3-like reaction-order modes at high conversion, respectively. DFT calculations showed that MgCo 2 O 4 (311) surface provided energetically favorable adsorption and activation sites for NH 3 and HClO 4 , while the synergistic effects of Co, Mg, and adjacent O sites facilitated intermediate conversion, alleviated the reaction stagnation between the LTD and HTD stages, and promoted the earlier onset and partial merging of HTD and LTD stages.