Wen-Sheng Dong

Conversion of cellulose to lactic acid catalyzed by erbium-exchanged montmorillonite K10

Various erbium ion-exchanged montmorillonite K10 materials were prepared by an ion exchange method and were found to act as efficient solid acid catalysts. The catalytic materials synthesized in this work were characterized using a combination of X-ray fluorescence spectroscopy, N2 adsorption, powder X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy and NH3 temperature-programmed desorption, as well as by FT-IR spectra analysis following pyridine adsorption. These catalysts were also evaluated with regard to the hydrothermal conversion of cellulose to lactic acid. Lactic acid yields as high as 67.6% were obtained when reacting 0.3 g cellulose, 0.1 g catalyst and 30 mL water at 240 °C under 2 MPa N2 for 30 min. Upon recycling of the catalyst, the lactic acid yields decreased from 67.6 to 58.7 to 55.9% during the first, second and third trials. Beginning with the second trial the catalyst behaved as a true heterogeneous catalyst for the conversion of cellulose to lactic acid. The observed decreases in catalytic activity during recycling could be due to a combination of erbium ion leaching, deposition of carbon species in pores and partial structural changes in the catalyst.

Ordered mesoporous BaCO 3 /C-catalyzed synthesis of glycerol carbonate from glycerol and dimethyl carbonate

BaCO3/C composites were synthesized by a multi-component co-assembly method combined with a carbonization process using phenolic resol as carbon source, barium nitrate as barium precursor, and triblock copolymer Pluronic F127 as template. The synthesized materials were characterized by X-ray diffraction, transmission electron microscopy, N2 physical adsorption, thermogravimetric analysis, and temperature-programmed desorption of CO2. When BaCO3 contents were increased from 9.1 wt% to 44.7 wt%, pore size increased from 3.1 to 4.3 nm and the BET (Brunauer-Emmett-Teller) surface area initially increased to a maximum value of 390 m2 g−1 (at a BaCO3 content of 18.5 wt%) before subsequently decreasing. BaCO3 was well dispersed in the amorphous carbon framework, and no phase separation was observed. The mesoporous Ba-CO3/C composites exhibited high catalytic activities toward the transesterification of glycerol and dimethyl carbonate into glycerol carbonate. A glycerol conversion of 97.8% and a glycerol carbonate selectivity of 98.5% were obtained under the optimized reaction conditions.

PtAu alloy nanoparticles supported on thermally expanded graphene oxide as a catalyst for the selective oxidation of glycerol

Thermally expanded graphene oxide (TEGO) supported PtAu alloy nanoparticles with various compositions was prepared, and then characterized using a combination of atomic absorption spectroscopy, powder X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. These catalysts were evaluated for the aerobic oxidation of glycerol in base-free aqueous solution. The results showed that PtAu(7 : 1)/TEGO exhibited the optimum activity for the conversion of glycerol among all the catalysts. Glycerol conversion of 60.4% and selectivities of 53.5% glyceric acid (GLYA), 25.7% glyceraldehydes (GLYDE), 11.6% dihydroxyacetone (DHA), and 3.8% glycolic acid (GLYCA) were obtained when reacting an aqueous solution of glycerol (0.3 M, 20 mL) at 60 °C under 0.3 MPa O2 for 4 h in the presence of 0.023 g PtAu(7 : 1)/TEGO catalyst. Moreover, the reusability of PtAu(7 : 1)/TEGO was investigated, and a reaction mechanism for the oxidation of glycerol was proposed.

Oxidative esterification of ethylene glycol in methanol to form methyl glycolate over supported Au catalysts

Au/ZnO and Au/Al2O3 catalysts with various mean Au particle diameters (2.0–7.4 nm) were prepared by the deposition of pre-formed Au colloids. These catalysts were evaluated in the oxidative esterification of ethylene glycol to methyl glycolate. The results show that the catalytic activity per surface Au atom is independent of Au particle diameter in the range of 3–7.4 nm, whereas smaller Au particles (~2.0 nm) show an inferior activity. This behavior was observed on both Au/ZnO and Au/Al2O3 catalysts. This observed correlation between activity and Au particle diameter confirms the assertion that only exposed atoms are catalytically active. We prepared gold nanoparticles with a uniform mean diameter of ~3 nm loaded on various supports, i.e. ZnO, Al2O3, SiO2, TiO2 and CeO2. Among these five catalysts, Au/ZnO gave the best catalytic activity in the reaction followed by Au/Al2O3. Au/SiO2, Au/TiO2 and Au/CeO2 gave significantly lower activities. The variation in catalytic behavior of these gold catalysts on different supports originates from differences in the anchoring of the supported Au particles, the gold oxidation state, the gold–support interaction, and the acidity of the support.

Comparative Study of Iron-Based Fischer–Tropsch Synthesis Catalysts Promoted with Strontium or Potassium

The effect of strontium as a chemical promoter on iron-based Fischer–Tropsch synthesis (FTS) catalysts was investigated and compared with that of potassium. Strontium was chosen for study because of its relationship to potassium through the Diagonal relationship in the Periodic Table. The catalysts were characterized by N2 physisorption, X-ray diffraction, laser Raman spectroscopy, Mössbauer effect spectroscopy, H2/CO temperature programmed reduction and temperature programmed hydrogenation. FTS reaction was tested in a fixed-bed reactor. It was found that strontium and potassium strengthened Fe-O bonds of iron oxides species, which is not favorable for the reduction of the catalysts in H2. Both of them enhanced the reduction and carbonization of the catalysts in CO and syngas atmosphere, suppressed the hydrogenation of surface carbon species, however, strontium is less effective than potassium. Besides, strontium improved the dispersion of iron oxide. Strontium did not significantly affect the activity of FTS and water gas shift (WGS), but facilitated the oxidation of iron carbides to Fe3O4 during FTS reaction process, while potassium significantly improved the FTS and WGS activity and inhibited the oxidation of iron carbide. Both of strontium and potassium decreased the selectivity of methane while facilitated the formation of heavy hydrocarbons and olefin, whatever, strontium exhibited a weaker effect compared to potassium.Graphical Abstract

Cu–Ag/hydrotalcite catalysts for dehydrogenative cross-coupling of primary and secondary benzylic alcohols

The development of new and inexpensive heterogeneous catalysts for direct C–C cross-coupling of primary and secondary alcohols is a challenging goal and has great importance in academic and industrial sectors. In this work Cu–Ag/hydrotalcite (Cu–Ag/HT) catalysts were prepared and tested for their impact on this cross-coupling. The effect of supports, including MgO, γ-Al2O3 and HT with different Mg:Al molar ratios, was investigated. It was found that the acidic or basic properties of the supports affected product selectivity. The roles of Cu and Ag sites in the cross-coupling were also investigated with the prepared Cu–Ag/HT catalyst demonstrating high activity and selectivity for the reaction. The yield-to-target product of β-phenylpropiophenone reached 99% after 1 h under optimum reaction conditions. The stability in air and reusability studies show that Cu–Ag/HT can be stored for 6 days and can be used five times without apparent deactivation, respectively.