Enhanced Water Activation via Alkali Metal-Modified Pd Clusters: A Key to Boosting HCHO and CO Oxidation

In heterogeneous catalysis, the presence of H₂O often has complex effects on the catalyst performance. It can both cause active site poisoning and play a positive role in certain reactions, such as HCHO and CO oxidation. However, H₂O activation and humidity adaptability remain significant challenges in low-temperature catalytic oxidation reactions. Herein, an ultraefficient Pd–O_x–K active site located within the silicalite-1 (S-1) zeolite (marked as K_x–Pd@S-1) was successfully constructed through an in situ encapsulation and alkali metal modification strategy. K_x–Pd@S-1 exhibits satisfactory low-temperature oxidation activity and durability in HCHO and CO removal. Experiments demonstrate that the addition of the alkali metal K significantly accelerates H₂O activation, generating abundant surface hydroxyl (−OH) species. Even under high-humidity (RH = 90%) conditions, K_0.5–Pd@S-1 exhibits remarkable H₂O resistance. Cycling tests reveal that K_0.5–Pd@S-1 has considerable repeatability and stability, with the HCHO conversion remaining at 98% even after 5 testing cycles. The enhanced activity is attributed to Pd–O_x–K sites, providing efficient adsorption and activation sites for reactants. Moreover, the reaction mechanism study confirms that reactive oxygen species (O₂^–, O₂^2–, and −OH) coaccelerate the degradation of key intermediate species. This work provides valuable insights into the design of efficient catalysts for practical applications.