First-principles methods for unraveling the structure–catalytic activity relationship and mechanism of δ-MnO2-supported metal cluster catalysts in ambient temperature benzene to CO2 degradation†

Benzene, a volatile cyclic aromatic hydrocarbon, is frequently discharged into the environment and poses serious threats to human health. However, the effective degradation of benzene at low temperatures remains a formidable challenge in the field of environmental remediation. In this study, a series of 49 catalyst samples, spanning from single atoms to trimers and tetramers, supported on δ-MnO₂ were meticulously constructed by employing the density functional theory (DFT) method. This approach facilitates an in-depth exploration of the structure–function relationship and enables the identification of prospective catalysts capable of degrading benzene into CO₂ and H₂O, thereby providing valuable insights for the development of efficient benzene degradation strategies at low temperatures. The obtained results unequivocally demonstrate that the separation between reaction products and reactants is substantially augmented with an increment in the number of active sites. Notably, the Ag₄ tetramer exhibits a remarkable enhancement in this regard. Further in-depth analyses reveal that the superior catalytic activity of Ag₄ relative to Pt₄ and Pd₄ tetramers can be ascribed to the closer energy alignment between the highest occupied molecular orbital (HOMO of Ag₄) and the lowest unoccupied molecular orbital (LUMO of benzene), which facilitates electron transfer and reaction initiation. To assess the practical catalytic effectiveness, a detailed analysis of the reaction pathways for benzene degradation was carried out. Remarkably, the energy barrier of the rate-determining step was determined to be merely 0.71 eV at room temperature, comparable to those achieved under photocatalytic and high-temperature conditions. This finding is of great significance as it represents the first successful degradation of benzene by precisely controlling the size of metal clusters. Overall, this study not only provides valuable theoretical insights for benzene abatement but also paves the way for remediating related pollutants, heralding a new approach in the pursuit of sustainable environmental protection strategies.