Pd@UiO‐66‐Type MOFs Prepared by Chemical Vapor Infiltration as Shape‐Selective Hydrogenation Catalysts

Abstract

AbstractHost‐guest inclusion properties of UiO‐66 and UiO‐67 metal‐organic frameworks have been studied using ferrocene (FeCp2) as probe molecule. According to variable‐temperature solid‐state 1H and 13C CP‐MAS‐NMR, two different environments exist for adsorbed FeCp2 inside UiO‐66 and UiO‐67, which have been assigned to octahedral and tetrahedral cavities. At room temperature, a rapid exchange between these two adsorption sites occurs in UiO‐67, while at –80 °C the intracrystalline traffic of FeCp2 through the triangular windows is largely hindered. In UiO‐66, FeCp2 diffusion is already impeded at room temperature, in agreement with the smaller pore windows. Palladium nanoparticles (Pd NPs) encapsulated inside UiO‐66 and UiO‐67 have been prepared by chemical vapor infiltration of (allyl)Pd(Cp) followed by UV light irradiation. Infiltration must be carried out at low temperature (–10 °C) to avoid uncontrolled decomposition of the organometallic precursor and formation of Pd NPs at the external surface of the MOF. The resulting Pd‐MOFs are shape selective catalysts, as shown for the hydrogenation of carbonyl compounds with different steric hindrance.