Rong-Zhen Yang

Catalytic dehydration of fructose to 5-hydroxymethylfurfural over Nb2O5 catalyst in organic solvent

The catalytic dehydration of fructose to 5-hydroxymethylfurfural (HMF) in DMSO was performed over Nb2O5 derived from calcination of niobic acid at various temperatures (300-700 °C). The catalysts were characterized by powder X-ray diffraction, N2 physical adsorption, temperature-programed desorption of NH3, n-butylamine titration using Hammett indicators, infrared spectroscopy of adsorbed pyridine, and X-ray photoelectron spectroscopy. It was found that both catalytic activity and surface acid sites decrease with increasing calcination temperatures. The Nb2O5 derived from calcination of niobic acid at 400 °C reveals the maximum yield of HMF among all the catalysts, although the amount of acid sites on the catalyst is lower than that on the sample calcined at 300 °C. The results suggest that the presence of larger amounts of strong acid sites on the surface of the Nb2O5 calcined at 300 °C may promote side reactions. The Nb2O5 prepared at 400 °C shows 100% fructose conversion with 86.2% HMF yield in DMSO at 120 °C after 2 h. The activity of the catalyst decreases gradually during recycle because of coke deposition; however, it can be fully recovered by calcination at 400 °C for 2 h, suggesting that this catalyst is of significance for practical applications.

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.

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.

An efficient catalytic system for the synthesis of glycerol carbonate by oxidative carbonylation of glycerol

Glycerol carbonate was synthesized by the oxidative carbonylation of glycerol catalyzed by the commercial Pd/C with the aid of NaI. High conversion of glycerol (82.2%), selectivity to glycerol carbonate (>99%), and TOF (900 h−1) were obtained under the conditions of 5 MPa (pCO:pO2 = 2:1), 140 °C, 2 h. The highly active palladium species were generated in situ by dissolution from the carbon support and stabilized by re-deposition onto the support surface after the reaction was finished. Palladium dissolution and re-deposition were crucial and inherent parts of the catalytic cycle, which involved heterogeneous reactions. This Pd/C catalyst could be recycled and efficiently reused for four times with a gradual decrease in activity. Moreover, the influences of various parameters, e.g., types of catalysts, solvents, additives, reaction temperature, pressure, and time on the conversion of glycerol were investigated. A reaction mechanism was proposed for oxidative carbonylation of glycerol to glycerol carbonate.