Encapsulation of Supported Metal Nanoparticles with an Ultra-Thin Porous Shell for Size-Selective Reactions

Heterogeneous catalysts are widely used. However, heterogeneous catalysts cannot selectively convert specific molecules in the reactant mixture to catalyze only desired reactions. Size-selective catalysts with a metal core and porous oxide shell have a promising structure that can increase the reaction selectivity through reactant molecular discrimination. This paper describes a general method to create porous metal oxide films with well-defined porous structures and precisely controlled thickness down to several angstroms from dense organic/inorganic hybrid metal alkoxide films grown by molecular layer deposition (MLD). A novel nanostructured catalyst with an ultra-thin porous shell obtained from the thermal decomposition of an aluminum alkoxide film deposited by MLD for size-selective reactions was developed. The molecular sieving capability of the porous metal oxide films was verified by examining the liquid-phase hydrogenation of n-hexene versus cis-cyclooctene. The success of making these materials by MLD opens up a new method for preparing size-selective catalysts.