Dendrimer-Stabilized Ru Nanoparticles Immobilized in Organo-Silica Materials for Hydrogenation of Phenols

Abstract

New hybrid catalysts based on Ru nanoparticles, encapsulated into poly(propylene imine dendrimers), immobilized into silica pores, were synthesized and examined for the hydrogenation of alkyl-substituted phenols. The corresponding alkyl-substituted cyclohexanols were presented as the major reaction products, while incomplete hydrogenation products appeared to be minor. A competition between the sterical factors of dendrimer-containing carriers and the electronic factors of substrate substituents influenced the hydrogenation rate of the alkyl-substituted phenols. The carrier structure was found to have a significant influence on both the physical and chemical properties of the catalysts and their hydrogenation activity. The synthesized hybrid catalysts appeared to be stable after recycling and could be re-used several times without significant loss of activity.

Selective Levulinic Acid Hydrogenation in the Presence of Hybrid Dendrimer‐Based Catalysts. Part I: Monometallic

“…Physical and chemical properties of the catalysts, used in the current work, are presented in Tables and . TEM images and XPS spectra are presented in the Supporting Information (Figures S1–S8).…”

“…As in ref. , the experimental reaction time, applied for TOF calculations, was the time at which the hydrogenation kinetic curve had a maximum slope, corresponding to 30–50 % conversions in the majority of cases. If an induction period took place, then the only time interval with maximum slope of the curve would be taken into account for TOF calculation.…”

“…Other factors, hindering the subsequent angelica lactone hydrogenation, may be attributed to local diffusion limitations, caused by dendritic ligands, as well as to the rigid and relatively bulky structure of angelica‐lactone requiring larger adsorption sites than the initial levulinic acid (of which only the carbonyl group must be adsorbed). The proceeding of the levulinic acid hydrogenation through the angelica lactone as the intermediate (not 4‐hydroxyvaleric acid) even in the absence of added water can be explained in terms of water molecules retained among polar dendrimer branches or by the silica framework or adsorbed on the surface of Ru nanoparticles …”

“…Recently, we have developed a new approach for the synthesis of dendrimer‐containing both amorphous and mesoporous organosilica materials by the sol–gel method, including cohydrolysis of Si(OEt) 4 with PPI dendrimers, modified with (3‐glycidoxy)propyltrimethoxysilane (Figure ) . Impregnated with Ru nanoparticles, these catalysts have been successfully applied for effective hydrogenation of phenols to corresponding cyclohexanols .…”

“… Structures of Ru hybrid catalysts based on PPI dendrimers, immobilized in silica pores: a) G3‐dendr‐SiO 2 ‐Ru; b) G2‐dendr‐ meso ‐SiO 2 ‐Ru …”