Pd Nanoparticles Encapsulated in FER Zeolite through a Layer Reassembling Strategy as Shape-selective Hydrogenation Catalyst

Noble metal nanoparticles (NPs) encapsulated in zeolites bearing distinct shape-selective properties at molecular level expand their new applications in catalysis. Here we report a synthesis strategy for the encapsulation of Pd NPs inside FER zeolite via a layer reassembling process. Pd precursors were introduced by swelling FER layers in RUB-36 through the surfactant cetyltrimethylammonium cations (CTA(+)) and then an ion-exchange process at ambient temperature. Pd@FER was formed with a uniform diameter distribution of Pd NPs at about 1.4 nm during the topotactic transformation from layered zeolite precursors to 3-dimensional zeolites followed by calcination. The as-prepared Pd@FER catalyst exhibits distinct shape-selective properties in hydrogenation reactions. It has relatively lower activity for 1-hexene and almost no activity for 1-phenyl-1-cyclohexene compared with Pd/RUB-37 catalyst prepared via wet impregnation due to the restrictions of channels in the FER zeolite. On the contrary, Pd@FER shows very high hydrogenation activity for benzaldehyde and very low activity for diphenylmethanone hydrogenation, while Pd/RUB-37 exhibits high hydrogenation activity for both benzaldehyde and diphenylmethanone. This synthesis strategy may be extended to other noble metals or two-dimensional layered zeolite systems for size-selective hydrogenation reactions.