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 (O-2(-), O-2(2-), and -OH) coaccelerate the degradation of key intermediate species. This work provides valuable insights into the design of efficient catalysts for practical applications.