Ti Substitution-Induced Inter-Site Distance Effect (ISDE) in Hierarchical Porous Cobalt Titanium Oxide Promoting Selective NH ₃ Oxidation for Enhanced Energy Release

The combustion efficiency and energy release capacity of solid rocket propellants (SRPs) are predominantly determined by the thermal decomposition behavior of ammonium perchlorate (AP), the core oxidizer. Developing high-efficiency catalysts and deciphering their intrinsic catalytic mechanisms remain a critical challenge. In this work, Ti 4+ substitution modulates the distance between Co–Co active sites, triggering a unique intersite distance effect (ISDE) in hierarchical porous Co 2 TiO 4 nanoflower catalysts. Their catalytic performance and intrinsic mechanism for AP thermal decomposition were systematically investigated. The shorter Co–Co active site distance enhances the electronic synergistic effect by enabling a stable “bridged adsorption” dual-site mechanism, potentially breaking the scaling relations between intermediate adsorption energies, and thus significantly improving catalytic performance. This ISDE synergizes with the hierarchical porous structure, optimizing the electronic structure of Co sites (the d-band center shifts 0.3 eV toward the Fermi level), enhancing the adsorption and activation capacity of reaction intermediates, and regulating the NH 3 oxidation pathway, increasing the selectivity of NO 2 to 48.4%, accompanied by an accelerated decomposition rate and more concentrated exothermic behavior. Density functional theory (DFT) calculations further verify that Ti substitution adjusts the surface electrostatic potential and adsorption energy of reactants, facilitating the cleavage of N–H and Cl–O bonds in NH 3 and HClO 4, respectively. This work clarifies the critical role of ISDE in mediating catalytic activity and provides a new theoretical paradigm for the rational design of high-performance bimetallic oxide catalysts for energetic material applications, particularly in SRPs.