Ag nanoparticles supported on wormhole HMS material as catalysts for CO oxidation: Effects of preparation methods

Ag nanoparticles supported on wormhole HMS material were prepared by in-situ reduction methods (post-assembly and in-situ incorporation methods). The catalysts were characterized by XRD, N2 adsorption–desorption, ICP-AES and TEM. It was found that the preparation methods strongly affected the structure of HMS and Ag particle size. Due to the protection of DDA in the reduction process, Ag nanoparticles with smallest size (4.5 nm) were obtained in in-situ incorporation method (TEOS was added into the mixture solution in the last procedure). Meanwhile, HCHO in the solution can react with DDA, resulting in the decrease of structural order and BET value of the sample. In post-assembly methods, the H-bonding between DDA and the inorganic Si species weakens the affinity of DDA for Ag species, resulting in the aggregation of Ag nanoparticles in the following reduction process. The catalytic activity of catalysts for low-temperature CO oxidation was studied here. Besides the size effect of Ag nanoparticles, it was believed that the structural order of the samples was also crucial for high catalytic activity.