Enhanced CO oxidation over Pd/MIL catalysts promoted by co-impregnated alkali and alkaline earth metals

The catalytic oxidation of carbon monoxide (CO) is a key process in environmental remediation and energy applications. Although metal oxides are commonly employed as supports, metal–organic frameworks (MOFs) offer superior surface area, porosity, and structural tunability, making them excellent platforms for exploring structure–activity relationships in heterogeneous catalysis. However, the role of alkali and alkaline earth metal (M) promoters on MOF-supported catalysts remains poorly understood. In this work, a series of PdM/MIL-101(Cr) catalysts were synthesized via co-impregnation using M = Mg, Ca, Ba, K, and Cs. Systematic characterization and catalytic testing revealed that even trace amounts of M metals can significantly enhance catalytic activity by improving Pd dispersion and strengthening Pd–support interaction during synthesis. Among all the prepared catalysts, PdMg/MIL demonstrated the highest CO oxidation performance, achieving complete CO conversion at a low temperature. A comparison with sequentially impregnated catalysts (Pd/M/MIL and M/Pd/MIL) confirmed that simultaneous co-impregnation is essential for guiding Pd to high-affinity sites within the MOF, thereby optimizing the properties of the active site. This study presents a novel approach to enhance Pd catalytic activity via co-impregnation with low-cost M promoters in MOF-supported systems. These insights provide new design strategies for advanced low-temperature oxidation catalysts.