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

Host-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. Encapsulation of Pd nanoparticles inside the pores of UiO-66 and UiO-67 by chemical vapor infiltration leads to shape-selective catalysts, as shown for the hydrogenation of carbonyl compounds of different steric hindrance.