Construction of Pd@K-Silicalite-1 via in situ encapsulation and alkali metal modification for catalytic elimination of formaldehyde at room temperature.

[Display omitted] • Pd@K-Silicalite-1 is prepared by the encapsulation strategy with K modification. • Pd@K-Silicalite-1 can completely remove HCHO at room temperature. • The addition of K induces the formation of Si-O-K-Pd and increases alkali sites. • Pd@K-Silicalite-1 possesses high dispersion and small size of Pd nanoparticles. • Pd@K-Silicalite-1 exhibits strong HCHO adsorption capacity. The Silicalite-1-encapsulated Pd catalyst with alkali metal K modification (Pd@K-Silicalite-1) was prepared via the hydrothermal method with ethylenediamine as ligand and KOH as precursor of K promoter. The introduction of K partially replaced H of silanol in Silicalite-1 and induced the formation of Si-O-K-Pd species, which were beneficial for the improvement of Pd dispersion. The Pd nanoparticles with a size of ca. 1.9 nm were uniformly encapsulated in the matrix of Silicalite-1 zeolite. The catalytic activity of Pd@K-Silicalite-1 was much better than those of Pd/Silicalite-1 and Pd@Silicalite-1 for HCHO oxidation, HCHO conversion could reach 100 % over Pd@K-Silicalite-1 (Pd content = 0.15 wt%) at room temperature under space velocity (SV) of 120,000 mL/(g × h) and relative humidity (RH) of 35 %. Based on the results of various characterization techniques, one can conclude that the improvement in catalytic activity of Pd@K-Silicalite-1 was attributable to high dispersion and small size of Pd NPs and enhanced HCHO adsorption capacities. In addition, we investigated the reaction mechanism of HCHO oxidation over the Pd@K-Silicalite-1 catalyst by in situ DRIFTS spectra. This work provides some guidance on developing high-performance catalysts for HCHO elimination via in situ encapsulation and alkali metal modification. [ABSTRACT FROM AUTHOR]