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.
Highlights
Hydrogenation of phenol is still an important process in the petrochemical industry, being used to obtain cyclohexanone, the essential feedstock for the synthesis of adipic acid and caprolactam [1,2,3].Hydrogenation products of substituted phenols are used as feedstock for synthesis of lubricants, additives to oils and fuels, surfactants, and perfumes
New organosilica hybrid catalysts based on Ru nanoparticles, encapsulated into poly(propylene dendrimers) and immobilized into silica pores, were synthesized using a sol-gel method
Both catalysts proved their efficiency in the hydrogenation of various phenols, appearing stable under two-phase conditions and not subjected to hydrolysis, which was a characteristic of earlier described Ru catalysts, based on cross-linked dendrimer networks
Summary
Hydrogenation of phenol is still an important process in the petrochemical industry, being used to obtain cyclohexanone, the essential feedstock for the synthesis of adipic acid and caprolactam [1,2,3]. Ru nanoparticles, stabilized by poly(N-vinylpyrrolidone) (PVP), supported on γ-Al2 O3 and exposed to microwave radiation in situ, appeared as good catalysts for selective hydrogenation of phenol to cyclohexanone (yield of 71% within 2 h), more active than conventional Ru/Al2 O3 [44]. It required much more severe reaction conditions (160 ◦ C, 50 MPa of H2 ) in comparison with homogeneous Ru/PVP catalyst [39]. Be obtained, in which individual complexes with metal ions and stabilize nanoparticles Such materials are excellent supports groups are covalently bonded to two or more Si atoms. Dendrimers (PPI, PAMAM) as templates for synthesis of nanoparticles and metal complex catalysts
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