| In this work, several transition-metal nanocatalysts have been prepared. They were applied in catalytic hydrogenation reactions and showed satisfactory results. The highly water-soluble palladium nanoparticles (NPs) were synthesized by using the amphiphilic poly(ethylene glycol)-functionalized dicationic imidazolium-based ionic liquid ([C12Im-PEG]Cl2) as a stabilizing agent. The aqueous dispersed palladium NPs in the range of1.9±0.3nm were observed by transmission electron microscopy (TEM). The physicochemical properties of [C12Im-PEG]Cl2in aqueous phase have been characterized by surface tension and Dynamic Light Scattering (DLS) measurements. It was demonstrated that the amphiphilic ionic liquid could form micelles above its critical micelle concentration (CMC) in aqueous solution and the micelles played a crucial role in stabilizing palladium NPs and thus promoted the catalytic hydrogenation. Furthermore, the dicationic ionic liquid can act also as a Gemini surfactant and generated emulsion between hydrophobic substrates and catalytic aqueous phase during the reaction. The aqueous dispersed palladium NPs showed efficient activity for the catalytic hydrogenation of various substrates under very mild conditions and the stabilizing Pd(0) nanoparticles (NPs) could be reused at least eight times with a complete conservation of activity.The use of transition metal nanoparticles/ionic liquid (IL) as a thermoregulated and recyclable catalytic system for hydrogenation has been investigated under mild condition. The functionalized ionic liquid was composed of poly(ethylene glycol)-functionalized alkylimidazolium as cation and tris-meta-sulfonato-phenylphosphine (P(C6H4-m-SO3-)3) as anion ([C12Im-PEG]1.5[tppt]). Simultaneously, ethyl acetate was chosen as the thermomorphic solvent to overcome the drawbacks like usage of toxic organic solvents in this contribution. Due to the cooperative effect regulated both cation and anion of ionic liquid, the nano-catalysts revealed distinguished temperature-dependent phase behavior and excellent catalytic properties, such as catalytic stability, activity and selectivity. For the hydrogenation of α,β-unsaturated aldehydes, palladium and rhodium nanopartciles stabilized by ionic liquid exhibited higher selectivity for the hydrogenation of the C=C bonds than the commercial catalyst (Pd/C and Rh/C). We believed that the anion of the ionic liquid, P(C6H4-m-SO3-)3, played a role in modification of the metal nanopaticles through the coordination capacity, changing the surrounding electronic characteristics of nanoparticles, while the poly(ethylene glycol)-functionalized alkylimidazolium cation provided the thermomorphic properties for the nano-catalysts in ethyl acetate. The present catalytic systems can be employed for the hydrogenation of a wide range of the substrates with different functional groups. The catalysts could be easily separated from products by phase separation and efficiently recycled ten times without significant changes in the catalytic activity.Sulfonic acid-functionalized silica-supported ruthenium catalyst (Ru/SiO2-SO3H) was employed for the hydrogenolysis of cellulose in a one-pot in neutral water medium. Ru/SiO2-SO3H was a bifunctional catalyst containing both Br(?)nsted acidic site and metal site (Ru). Compared with the mechanical mixture of silica-supported Br(?)nsted acid (SiO2-SO3H) and silica-supported Ru catalyst (Ru/SiO2), the bifunctional catalyst showed much higher yield to sorbitol, which can reach up to61.2%when the reaction was performed for10h at150℃. Through the characterizations of XPS and pyridine-adsorbed FT-IR, it was observed the existence of the interaction between sulfonic groups and Ru nanoparticles in Ru/SiO2-SO3H catalyst. The sulfonic acid groups and metal sites in the adjacent position were important for enhancing the yield of sorbitol. In addition, the present catalyst can be reused five times with only a slight decrease in yield of sorbitol in the consecutive recycles. |
PDF Full Text Request