Wenwen Zhu

Efficient hydrogenolysis of cellulose into sorbitol catalyzed by a bifunctional catalyst

A sulfonic acid-functionalized silica-supported ruthenium catalyst (Ru/SiO2–SO3H) was employed for the hydrogenolysis of cellulose in one pot in neutral water medium. Ru/SiO2–SO3H is a bifunctional catalyst containing both a Bronsted acidic site and a metal site (Ru). Compared with the mechanical mixture of a silica-supported Bronsted acid (SiO2–SO3H) and a silica-supported Ru catalyst (Ru/SiO2), the bifunctional catalyst showed much higher yield of sorbitol, which could reach up to 61.2% when the reaction was performed for 10 h at 150 °C. Through the characterization by XPS and pyridine-adsorbed FT-IR, the existence of the interaction between sulfonic groups and Ru nanoparticles in the Ru/SiO2–SO3H catalyst was observed. 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.

Gas phase dehydration of glycerol to acrolein catalyzed by zirconium phosphate

Abstract Zirconium phosphates were prepared by precipitation, hydrothermal synthesis, and impregnation methods and were characterized by X-ray diffraction, thermogravimetric analysis, nitrogen adsorption, Fourier transform infrared spectroscopy, and Hammett indicators. The different preparation methods have crucial effects on the texture and surface acidity of the zirconium phosphates. The zirconium phosphates were employed as catalysts for the gas phase dehydration of glycerol under mild reaction conditions. The zirconium phosphates from the precipitation method afforded the highest activity with the complete conversion of glycerol, 81% selectivity to acrolein, and no obvious deactivation over 24 h. Surface acidic sites played an important role in the activity, selectivity to acrolein, and life of catalysts.

Cooperative effects in catalytic hydrogenation regulated by both the cation and anion of an ionic liquid.

The use of transition-metal nanoparticles/ionic liquid (IL) as a thermoregulated and recyclable catalytic system for hydrogenation has been investigated under mild conditions. The functionalized ionic liquid was composed of poly(ethylene glycol)-functionalized alkylimidazolium as the cation and tris(meta-sulfonatophenyl)phosphine ([P(C(6)H(4)-m-SO(3))(3)](3-)) as the anion. Ethyl acetate was chosen as the thermomorphic solvent to avoid the use of toxic organic solvents. Due to a cooperative effect regulated by both the cation and anion of the ionic liquid, the nanocatalysts displayed distinguished temperature-dependent phase behavior and excellent catalytic activity and selectivity, coupled with high stability. In the hydrogenation of α,β-unsaturated aldehydes, the ionic-liquid-stabilized palladium and rhodium nanoparticles exhibited higher selectivity for the hydrogenation of the C=C bonds than commercially available catalysts (Pd/C and Rh/C). We believe that the anion of the ionic liquid, [P(C(6)H(4)-m-SO(3))(3)](3-), plays a role in changing the surrounding electronic characteristics of the nanoparticles through its coordination capacity, whereas the poly(ethylene glycol)-functionalized alkylimidazolium cation is responsible for the thermomorphic properties of the nanocatalyst in ethyl acetate. The present catalytic systems can be employed for the hydrogenation of a wide range of substrates bearing different functional groups. The catalysts could be easily separated from the products by thermoregulated phase separation and efficiently recycled ten times without significant changes in their catalytic activity.

The Role of Inorganic Oxide Supports in Synthesis of Cyclic Carbonates from Carbon Dioxide and Epoxides

Abstract An inorganic oxide support coupled with a quaternary ammonium salt is an efficient catalyst for the cycloaddition of CO2 and epoxide to produce cyclic carbonates under relatively mild reaction conditions (90 °C, 4 MPa). When tetrabutylammonium bromide (TBAB) was used alone, the activity of the cycloaddition reaction between carbon dioxide and epoxide was only moderate. When an inorganic oxide, especially one that has abundant surface hydroxyl groups was also employed, the reaction was accelerated significantly. This demonstrated that the inorganic oxide and TBAB had a strong synergetic effect for the cycloaddition reaction. Silica was chosen as a model oxide to study the role of surface hydroxyl groups in the reaction. When the surface of silica was silylated with trimethylchlorosilane or dimethyldichlorosilane, the catalytic activity decreased sharply due to surface silylation, which indicated clearly that the surface hydroxyl groups on the silica played a decisive role in influencing the catalytic activity.

Fluorescence sensing of iodide and bromide in aqueous solution: anion ligand exchanging and metal ion removing

A new rhodamine-based fluorescent probe RSP was facilely synthesized. Interestingly, the RSP-Hg-ClO4 ensemble can serve as a selective fluorescent probe for iodide and bromide based on metal ion removal and anion ligand exchanging, which is a novel rhodamine-based fluorescence sensing mechanism. Moreover, RSP can recognise Hg2+ selectively in 99% aqueous solution.

A Ti-substituted polyoxometalate as a heterogeneous catalyst for olefin epoxidation with aqueous hydrogen peroxide

The Ti-substituted polyoxometalates ([C12mim]5PTiW11O40, [CTA]5PTiW11O40 and [TBA]5PTiW11O40) were prepared and characterized by FT-IR, NMR, UV-vis and ICP-AES. Then the polyoxometalates (POM) were used as catalysts for the epoxidation of various olefins. It was found that the organic countercations had a considerable effect on the catalytic performance. In addition, UV-vis and the FT-IR spectroscopy indicated that the peroxo structure regarded as the active site for oxygen transfer was present even after the reaction, which led to the increasing reaction rate in the second run due to the disappearance of the induction period, as compared with that in the first run. A heterogeneous reaction mechanism has been suggested in olefin epoxidation catalyzed by a Ti-substituted polyoxometalate ([C12mim]5PTiW11O40) with aqueous hydrogen peroxide in ethyl acetate. The heterogeneous POM catalyst can be easily separated and recycled eight times without decreasing the catalytic activities.

Ionic liquid-Pluronic P123 mixed micelle stabilized water-soluble Ni nanoparticles for catalytic hydrogenation.

Ionic liquid (1-butyl-2,3-dimethylimidazolium acetate, [BMMIm]OAc)-Pluronic P123 mixed micelle stabilized water-soluble Ni nanoparticles were characterized by UV-vis, XRD, XPS and TEM and then employed for catalytic hydrogenation. It was demonstrated that the mixed-micelle stabilized Ni NPs showed excellent catalytic performance for the selective hydrogenation of CC and nitro compounds in the aqueous phase under very mild reaction conditions, and also the Ni NPs catalysts can be recycled at least for eight times without significant decrease in catalytic activity. The results of characterization revealed that the mixed micelle-stabilized Ni NPs catalysts were highly dispersed in aqueous phases even after five catalytic recycles. In addition, adding ionic liquid ([BMMIm]OAc) can affect the micelle structure of P123 solutions and thus afford an additional steric protection from aggregation of Ni NPs, resulting in enhancing stability and catalytic activity of Ni NPs.

Nanostructured Maghemite-Supported Silver Catalysts for Styrene Epoxidation

The supported silver catalyst Ag/KOH-γ-Fe2O3 was prepared by simple impregnation and liquid reduction and then structurally characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The supported silver catalysts were highly efficient for the epoxidation of styrene using tert-butyl hydroperoxide as the oxidant and ethyl acetate as the reaction medium. The addition of KOH was found to increase the catalytic activity and selectivity significantly. Additionally, the magnetically recoverable γ-Fe2O3, as a support, allowed for an easy separation and recycling of the catalyst after the reaction.

Immobilization of polyoxometalate-based ionic liquid on carboxymethyl cellulose for epoxidation of olefins

A novel ionic liquid consisting of a PEG-functionalized ammonium cation and a lacunary-type phosphotungstate anion was synthesized and characterized structurally. The ionic liquid was then immobilized onto environmentally benign polymer-carboxymethyl cellulose by two different routes: the impregnation method and the co-precipitation method. The immobilized ionic liquid can be used as a catalyst for olefin epoxidation with aqueous hydrogen peroxide in ethyl acetate. It was found that both of the immobilized ionic liquid catalysts showed better catalytic activities and stability than the homogeneous analogue in consecutive runs. In particular, the ionic liquid catalyst immobilized by the co-precipitation method afforded a higher catalytic stability than the catalyst immobilized by the impregnation method. It is suggested that the crucial factor influencing the catalytic performance is the difference in the interactions between the heteropoly anions and the polymer supports.

Ionic Liquid–Catalyzed Internal Redox Esterification Reaction

Abstract The internal redox esterification of α,β-unsaturated aldehydes and alcohols was carried out using different ionic liquids (ILs) as catalysts and reaction solvents. The basic ionic liquid, 1-butyl-3-methylimidazolium acetate ([bmim]OAc), exhibited the best activity for this reaction. The influences of the amount of ionic liquid catalyst and reaction time on yield of saturated ester have been investigated. The results showed that ionic liquid anions have a crucial effect on the redox esterification of α,β-unsaturated aldehydes and alcohols. The nucleophilic carbenes generated in situ from the ionic liquid cation were believed to be actual active species for this reactions. GRAPHICAL ABSTRACT