Insights into the structure–property–activity relationship in molybdenum-doped octahedral molecular sieve manganese oxides for catalytic oxidation

Abstract

Hexavalent molybdenum ions substituted into the mixed-valent framework of octahedral molecular sieve manganese oxides (1–10 mol% Mo–K-OMS-2) were systematically prepared via a single-step refluxing method. The structure, composition, morphology, thermal stability, and textural and redox properties of the Mo–K-OMS-2 materials were characterized by various experimental techniques. Density functional theory (DFT) calculations were performed to study the electronic properties of K-OMS-2 materials, including the influence of molybdenum on such properties. The catalytic activity of K-OMS-2 towards CO oxidation dramatically increased with Mo dopant concentration, until an optimum incorporation of 5 mol% was reached, giving full CO conversion at 120 °C (1 vol% CO, 1 vol% O₂). More importantly, the activity of the 5% Mo–K-OMS-2 catalyst was (reversibly) inhibited by water vapour (3%) in the feed only at low temperatures and exhibited better tolerance and stability during long-run experiments (28 h) as compared to undoped K-OMS-2. The superior performance of Mo–K-OMS-2 catalyst for CO oxidation can be attributed to the following factors: (1) morphological evolution from nanofibers to nanospheres, as well as the slightly distorted structure, generated a sharp increase in the specific surface area up to 258 m² g⁻¹, hence, increased the number of surface active sites; (2) improved mobility of reactive oxygen species at the surface and enhanced redox properties; and (3) tailored electronic properties promoted more active sites for oxidation reactions, which is supported by DFT calculations.