Interfacial synergism of surface oxygen and cation redox chemistry in Co3O4–Mn3O4 heterostructures for low-temperature catalytic oxidation (LTCO) of benzene: stable humid-state activity after initial water inhibition

Introduction Low-temperature catalytic oxidation (LTCO) is a promising route to mitigate hazardous aromatic volatile organic compounds (VOCs) such as benzene, yet catalyst activity and water inhibition remain significant challenges. Objectives This study aims to develop dual-phase Co 3 O 4 –Mn 3 O 4 heterostructures (CM-x; x = Co/Mn molar ratio of 0.3–3) for the LTCO of dilute benzene and to elucidate how phase distribution, surface oxygen speciation, reducibility, and water adsorption govern performance under humid conditions (RH = 0–100%). Methods CM-x heterostructures were synthesized by coprecipitation and evaluated in a fixed-bed reactor for the oxidation of 10 ppm benzene at 50–550 °C under varying relative humidity (RH = 0–100%). Results Under dry-feed conditions, CM-1 exhibits the highest benzene oxidation activity, with T 50 = 227 °C and T 90 = 317 °C, and the most favorable balance between deep oxidative mineralization and CO 2 formation. At 250 °C, its mass-normalized benzene oxidation rate (5.06 × 10 −5 mol·gcat −1 ·h −1 ) exceeds those of CM-3, CM-0.3, Co 3 O 4 , and Mn 3 O 4 by factors of 1.1, 1.6, 7.8, and 20.3, respectively. Although the steady-state activity of CM-1 declines by ≈ 49% at 50% RH relative to the dry phase, a stable activity plateau is reached as humidity increases from 50 to 100% RH. These trends are consistent with redox synergy between Co 3+ /Co 2+ and Mn 4+ /Mn 3+ /Mn 2+ , coupled with changes in lattice and surface oxygen species, which together promote benzene activation and the subsequent deep oxidative mineralization of oxygenated intermediates to CO 2 . Conclusion The Co/Mn ratio in Co 3 O 4 –Mn 3 O 4 heterostructures thus governs benzene oxidation through coupled changes in phase distribution, surface oxygen speciation, reducibility, and water adsorption, underscoring the potential of these dual-phase oxides for the low-temperature thermocatalytic abatement of aromatic VOCs.