Lattice-confined manganese promoter weakens CoO covalency in tricobalt tetraoxide for enhanced oxidation of toluene to benzaldehyde

While electronic promoters are extensively employed to boost the reactivity of host catalysts, they frequently suffer from instability due to migration and leaching. To address this, confinement within the host catalyst has emerged as an effective strategy, with the specific location of confinement being a critical determinant of the promoter's effectiveness. Herein, we demonstrated that lattice-confining atomic Mn into the Co 3 O 4 lattice could effectively weaken the Co O covalency, thereby boosting the selective oxidation of toluene to benzaldehyde. The incorporated Mn, serving as an electronic promoter, formed oxygen-bridged Co-O-Mn bonds, which directly accounted for the attenuation of Co O covalency and the enhanced catalytic oxidation reaction efficiency. Among the atomic Mn-confined spinel Co 3 O 4 samples, the synthesized 0.5Mn-Co 3 O 4 sample exhibited the most outstanding performance, achieving a 79.2% toluene conversion and a 73.9% benzaldehyde selectivity within 6 h of reaction. This eminent catalytic performance was primarily attributed to the Mn-induced weakening of Co O bond covalency, which was accompanied by an increased specific surface area, a higher oxygen vacancy concentration due to lattice expansion, and enhanced dynamic lattice oxygen cycling facilitated by the lattice-confined Mn promoter. According to quenching experiments and in-situ Fourier transform infrared (in-situ FTIR) characterizations, the possible dynamic lattice oxygen cycling reaction mechanism was proposed over the oxygen-bridged Co-O-Mn bonds. Furthermore, the synthesized 0.5Mn-Co 3 O 4 sample displayed excellent stability and recyclability for more than five consecutive cycles.