PREPARATION AND CHARACTERIZATION OF MONTMORILLONITE-SUPPORTED PALLADIUM HYDROGENATION CATALYSTS POSSESSING MOLECULAR-SIEVING PROPERTIES

Highly dispersed palladium metal has been deposited in the interlayer space of montmorillonite clay by the reduction of intercalated palladium complexes. The use of the highly electrophilic Pd(Il) precursor complexes [Pd(PPh3)(NCMe)3]2+ and [PdL4]2+ (L = NCMe, (CH3)2CO) is shown to facilitate the reduction step under very mild conditions (0°C; MeOH as reaction medium). TEM analysis of reduced [Pd(PPh3)(NCMe)3]2+/clay and [Pd(NCMe)4]2+/clay samples reveals that the palladium is present largely in the interlamellar regions of the clay, in the latter case as particles of platelet morphology. A procedure for depositing palladium metal exclusively in the interlamellar region of the clay particles is also described. Transmission electron micrographs of the resulting material (containing 1 wt% Pd) reveal a very narrow size distribution for the palladium crystallites formed, the median particle diameter being ca. 8 Å. Consistent with this is an observed basal spacing of 8-10 Å for the intercalated regions of the clay. Molecular sieving effects are observed when this material is used as a catalyst for the hydrogenation of cyclic and monosubstituted alkenes of varying critical dimension. In contrast, catalysts prepared by simple reduction of Pd(II) complexes homogeneously dispersed in montmorillonite show significantly less shape selectivity towards olefinic reactants. © 1993 Academic Press, Inc.