DESIGN, CHARACTERIZATION AND APPLICATION OF HETEROGENEOUS SILICA SUPPORTED CATALYSTS, BASED ON PD NANOPARTICLES AND METAL SINGLE SITES (RH, CU)

The immobilization of metal NPs and metal single sites on silica support materials offers an interesting approach to heterogeneized catalysts for a multitude of different reactions. Selective hydrogenation reactions of prochiral substrates, such as (hetero-)aromatics, can be catalyzed by heterogeneized “hybrid catalysts” of the type RhI-Pd0/SiO2, consisting of silica-supported PdNPs and chiral Rh(I) phosphine single sites. These new “hybrid catalysts” were reported in the recent years, revealing the synergetic effect between Pd and Rh. Regarding the hydrogenation of benzene/toluene, it could be shown that RhI-Pd0/SiO2 are 4 times more active than Pd0/SiO2. In particular, the scope of this work was the extension of the “hybrid catalysts” by the use of chiral phosphine ligands. PdNPs were immobilized onto various mesoporous silica supports, having an ordered (e.g. MCM-41, SBA-15) or a non-ordered (e.g. Davisil B, Davison 62) structure, both in powdery form and as monoliths. Different immobilization methods were tested (impregnation, ionic exchange, CVD), whereupon CVD proved to be a promising procedure, giving high Pd loadings up to 1.95 wt % (expected: 2 wt %). Moreover, this method was suitable for both powdery silica materials and silica monoliths. Silica-supported chiral Cu(I) complexes of the type [CuI(PC-L*)]CF3SO3/SiO2 can be applied in the asymmetric cyclopropanation of -methyl styrene with ethyl diazoacetate (EDA). Regarding the different mesoporous ordered- and non-ordered silica supports (MCM-41, SBA-15, Davisil B, Aerosil, basic silica), SBA-15 turned out to be the most-suitable one, giving excellent Cu loadings up to 1.79 wt %. The application of the [CuI(PC-L*)]CF3SO3/SiO2 catalysts gave the cyclopropanes in high yields (83 %). In this context, the recyclability of [CuI(PC-L*)]CF3SO3/SiO2 could be proven. Silica monoliths are very advantageous and thus gladly used as support material: Besides their easy handling, they allow to work in flow conditions without packing a reactor. Within this work, silica monoliths were grafted and subsequently applied in the dehydration of fructose to 5-hydroxymethylfurfural (HMF). It was shown that the reaction works in batch as well as in flow, both homogeneously (using the sole unsupported grafting agent) and heterogeneously (using blank or grafted silica monoliths).