Enhanced moisture tolerance and toluene oxidation activity of δ-MnO₂ catalysts by Sn doping: Phase transition and surface protection

Effective and durable catalysts for removing volatile organic compounds (VOCs) like toluene are essential for reducing air pollution and protecting the environment. Manganese oxide-based catalysts have attracted significant attention for toluene oxidation due to their excellent catalytic performance and favourable physicochemical properties. However, the durability of MnO₂-based catalysts in humid atmospheres remains a challenge, as water vapor usually has a significant negative effect on their performance. To address this issue, we have synthesized a series of Sn-doped δ-MnO₂ catalysts that exhibit both water stability and high activity in the catalytic oxidation of toluene. An optimal amount of Sn doping induces a phase transformation in MnO₂, leading to the coexistence of a dual-phase structure. At the same time, Sn provides surface protection for MnO₂. After a thorough investigation of the acidic sites and the process of water adsorption/desorption, we found that the incorporation of Sn effectively regulates the acidity of the surface and influences the water adsorption/desorption behaviour of the MnO₂ surface. Consequently, a remarkable improvement in the conversion rate and water resistance associated with the catalytic oxidation of toluene was achieved by simply doping with Sn. This study presents a rational design strategy for developing MnO₂-based catalysts with enhanced efficiency and durability in humid environments, advancing catalytic solutions for toluene pollution control.