Performance of Fe─Mo Catalysts with Li/Na/K Promoters for Methanol Oxidation to Formaldehyde

Abstract Fe─Mo catalysts are widely employed in the commercial oxidation of methanol to formaldehyde. This study investigates the influence of alkali metal promoters (Li, Na, and K) on the morphology, structure, surface properties, and catalytic performance of Fe─Mo catalysts. A comprehensive array of characterization techniques, including SEM‐EDS, XRD, FTIR, Raman, XPS, NH 3 ‐TPD, and BET, was utilized to gain insights into these effects. The incorporation of alkali metal promoters was found to significantly modify the chemical composition and surface characteristics of the catalysts. Sodium and potassium promoters enhanced the formation of lamellar morphologies, promoted the segregation of molybdenum oxide crystals on the catalyst surface, and reduced the specific surface area. Additionally, they decreased the electron density around molybdenum atoms, lowered lattice oxygen content, and reduced catalytic activity. In contrast, lithium promoters suppressed lamellar morphology, facilitated the formation of a homogeneous cluster structure, and increased the concentration of bulk‐phase molybdenum oxide, thereby improving catalyst selectivity. Surface acidity analysis revealed that dimethyl ether, a by‐product, was predominantly formed on acidic sites. Optimization of lithium content further demonstrated that the catalyst achieved maximum formaldehyde selectivity at a Li/Mo molar ratio of 5%. These findings shed light on the role of alkali metal promoters in tailoring the properties of Fe─Mo catalysts and offer valuable guidance for the design and optimization of advanced catalysts for methanol oxidation.