Huizhen Liu

Selective Phenol Hydrogenation to Cyclohexanone Over a Dual Supported Pd–Lewis Acid Catalyst

Cooperative Reduction Selective redox transformation remains a general challenge in chemical synthesis. All too often, the most readily available precursor to a compound must be over-reduced (or over-oxidized) and then carefully coaxed back to a desired intermediate state. Such is the case with the synthesis of cyclohexanone, which is mass-produced for use in the preparation of nylon: Access by direct reduction of phenol is plagued by the rapid addition of too many hydrogen atoms to the substrate, producing an alcohol (cyclohexanol) in place of the ketone. Liu et al. (p. 1250) have discovered that the unexpected cooperation of supported palladium and a Lewis acid such as aluminum trichloride—two catalysts widely used alone but rarely in concert—facilitates highly selective conversion of phenol to cyclohexanone near room temperature. The key appears to be inhibition of the undesired ketone-to-alcohol reduction step by the Lewis acid. The cooperation of two common catalysts unexpectedly facilitates selective synthesis of a commodity chemical compound. Cyclohexanone is an industrially important intermediate in the synthesis of materials such as nylon, but preparing it efficiently through direct hydrogenation of phenol is hindered by over-reduction to cyclohexanol. Here we report that a previously unappreciated combination of two common commercial catalysts―nanoparticulate palladium (supported on carbon, alumina, or NaY zeolite) and a Lewis acid such as AlCl3―synergistically promotes this reaction. Conversion exceeding 99.9% was achieved with >99.9% selectivity within 7 hours at 1.0-megapascal hydrogen pressure and 50°C. The reaction was accelerated at higher temperature or in a compressed CO2 solvent medium. Preliminary kinetic and spectroscopic studies suggest that the Lewis acid sequentially enhances the hydrogenation of phenol to cyclohexanone and then inhibits further hydrogenation of the ketone.

Cycloaddition of CO2 to epoxides catalyzed by imidazolium-based polymeric ionic liquids

A series of cross-linked ionic polymers based on styrene-functionalized imidazolium salts with chloride, hexafluorophosphate, or tetrafluoroborate counter anions have been prepared and characterized using a range of analytical and spectroscopic techniques and electron microscopy. The polymer with the chloride anion is an efficient catalyst for the cycloaddition of carbon dioxide with epoxides to afford cyclic carbonates. The cross-linked polymer is insoluble in organic solvents and is highly stable and therefore can be easily recycled and reused.

Hydrogenolysis of glycerol catalyzed by Ru-Cu bimetallic catalysts supported on clay with the aid of ionic liquids

Glycerol is a well-known renewable chemical, and its effective transformation to valuable chemicals accords well with the principles of green chemistry. In this work, a series of Ru-Cu bimetallic catalysts were prepared using cheap and abundant clay, bentonite, as the support. Bentonite was modified with a functional ionic liquid 1,1,3,3-tetramethylguanidinium lactate (TMGL) in an attempt to develop highly efficient catalysts. Hydrogenolysis of aqueous solution of glycerol was performed with the immobilized Ru-Cu catalyst under temperatures of 190–240 °C and pressures of 2.5–10 MPa. The bimetallic catalysts were very efficient for promoting the hydrogenolysis of glycerol. 100% of glycerol conversion and 85% yield of 1,2-propanediol could be achieved at 230 °C and 8 MPa. The conversion of glycerol and the selectivity to 1,2-propanediol did not decrease after the catalyst was used 5 times. TMGL played a crucial role in fabricating the new catalysts. The catalysts were characterized by FT-IR, XPS, SEM and TEM, and the reasons for the excellent performances of the catalyst were also discussed.

One-pot conversion of CO2 and glycerol to value-added products using propylene oxide as the coupling agent

The effective conversion of carbon dioxide (CO2) and glycerol is an interesting topic in green chemistry. In this work, we studied the simultaneous transformation of CO2 and glycerol to value-added products using propylene oxide (PO) as coupling agent catalyzed by alkali metal halides. The effects of reaction temperature, CO2 pressure, reaction time, amount of catalyst, and PO to glycerol molar ratio on the reaction were investigated. It was discovered that the coupled catalytic reaction could produce glycerol carbonate (GC), propylene glycol (PG) and propylene carbonate (PC) very effectively using KI, an abundant and cheap salt, as the catalyst. The main reasons are that glycerol and PG are not only the reactant and product, respectively, but also act as the effective co-catalysts to promote the key step of the coupled reaction, and the reaction is thermodynamically favorable. This effective and atom economic route to convert glycerol and CO2 simultaneously has great potential application.

Molybdenum–Bismuth Bimetallic Chalcogenide Nanosheets for Highly Efficient Electrocatalytic Reduction of Carbon Dioxide to Methanol

Methanol is a very useful platform molecule and liquid fuel. Electrocatalytic reduction of CO2 to methanol is a promising route, which currently suffers from low efficiency and poor selectivity. Herein we report the first work to use a Mo-Bi bimetallic chalcogenide (BMC) as an electrocatalyst for CO2 reduction. By using the Mo-Bi BMC on carbon paper as the electrode and 1-butyl-3-methylimidazolium tetrafluoroborate in MeCN as the electrolyte, the Faradaic efficiency of methanol could reach 71.2 % with a current density of 12.1 mA cm(-2) , which is much higher than the best result reported to date. The superior performance of the electrode resulted from the excellent synergistic effect of Mo and Bi for producing methanol. The reaction mechanism was proposed and the reason for the synergistic effect of Mo and Bi was discussed on the basis of some control experiments. This work opens a way to produce methanol efficiently by electrochemical reduction of CO2 .

Ru–Zn supported on hydroxyapatite as an effective catalyst for partial hydrogenation of benzene

Design and preparation of efficient and greener catalytic systems for partial hydrogenation of benzene to cyclohexene is an interesting topic in green chemistry. In this work, Ru and Ru–Zn catalysts supported on hydroxyapatite (HAP), which is nontoxic and abundant in nature, were prepared via the simple ion-exchange method. The catalysts were characterized by powder X-ray diffraction (XRD), transmission electron spectroscopy (TEM), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption–desorption methods. The influences of Ru/Zn molar ratio, reaction temperature, pressure, reaction time, and amount of modifier NaOH on the partial hydrogenation of benzene were studied in detail. It was demonstrated that metallic nanoparticles of less than 2 nm were dispersed uniformly on the surface of the HAP, and the bimetallic Ru–Zn/HAP catalysts showed high activity and selectivity. The yield of cyclohexene could reach 33% over Ru–Zn/HAP at the optimized conditions, and the catalyst could be reused at least four times without obvious loss of the activity and selectivity.

Efficient Reduction of CO2 into Formic Acid on a Lead or Tin Electrode using an Ionic Liquid Catholyte Mixture

Highly efficient electrochemical reduction of CO2 into value-added chemicals using cheap and easily prepared electrodes is environmentally and economically compelling. The first work on the electrocatalytic reduction of CO2 in ternary electrolytes containing ionic liquid, organic solvent, and H2 O is described. Addition of a small amount of H2 O to an ionic liquid/acetonitrile electrolyte mixture significantly enhanced the efficiency of the electrochemical reduction of CO2 into formic acid (HCOOH) on a Pb or Sn electrode, and the efficiency was extremely high using an ionic liquid/acetonitrile/H2 O ternary mixture. The partial current density for HCOOH reached 37.6 mA cm(-2) at a Faradaic efficiency of 91.6 %, which is much higher than all values reported to date for this reaction, including those using homogeneous and noble metal electrocatalysts. The reasons for such high efficiency were investigated using controlled experiments.

Biomass-derived γ-valerolactone as an efficient solvent and catalyst for the transformation of CO2 to formamides

Efficient conversion of carbon dioxide (CO2) into valuable chemicals is a very attractive topic. Herein, we conducted the first work on the utilization of biomass-derived γ-valerolactone (GVL) as the solvent and catalyst for transformation of CO2 with various primary and secondary amines in the presence of phenylsilane (PhSiH3), and the corresponding desired formamides were produced with high yields without any additional catalyst. Systematic studies indicated that the lactone structure of GVL played a key role in the formation of the active silyl formates and the activation of N–H bonds in amines, thus leading to the excellent performance of GVL for the catalytic reactions.

Highly selective benzene hydrogenation to cyclohexene over supported Ru catalyst without additives

The Ru/ZnO–ZrOx(OH)y catalyst is very efficient for the selective hydrogenation of benzene to cyclohexene, and the yield of cyclohexene can reach 56% without using any additive. This work provides a highly efficient, cheap and clean method to produce cyclohexene.

Copper-catalyzed N-formylation of amines with CO2 under ambient conditions

We carried out work on N-formylation of amines with CO2 and PhSiH3 to produce formamides catalyzed by a copper complex. It was found that the Cu(OAc)2–bis(diphenylphosphino)ethane (dppe) catalytic system was very efficient for these kind of reactions at room temperature and 1 atm CO2 with only 0.1 mol% catalyst loading.