Liguo Wang

Magnesium oxide nanosheets as effective catalysts for the synthesis of diethyl carbonate from ethyl carbamate and ethanol

A series of MgO catalysts were prepared by thermal decomposition and precipitation methods. Their catalytic performance was evaluated in the synthesis of diethyl carbonate (DEC) from ethyl carbamate (EC) and ethanol. Among them, MgO prepared using sodium carbonate as the precipitant and calcined at 450 °C (MgO-SC-450) exhibited much higher catalytic activity. An excellent DEC yield of 58.0% with a high DEC selectivity of 92.1% could be achieved over the MgO-SC-450 catalyst under optimized reaction conditions: 210 °C, ethanol/EC molar ratio of 10, and 3 h. Moreover, the catalytic activity could be essentially retained during recycling experiments. The structure and surface basicity of the MgO catalysts were characterized by X-ray diffraction (XRD), Mastersizer 2000, N2 adsorption, field-emission scanning electron microscopy (FE-SEM), and temperature-programmed desorption of CO2 (CO2-TPD). It was found that MgO-SC-450 possessed nanosheet morphology. Furthermore, a larger amount of appropriate medium basic β sites of MgO-SC-450 with the peak located between 225 °C and 275 °C was favourable for obtaining much superior catalytic activity. Quasi in situ FT-IR experiments were carried out to elucidate the adsorption behaviours of reactants. It was found that EC could be effectively activated and ethanol could be dissociated to a strong nucleophilic ethoxy group by MgO. In addition, theoretical calculation proved the co-adsorption of EC and ethanol on the MgO surface. Based on the results of quasi in situ FT-IR experiments and theoretical calculation, a plausible reaction mechanism has been proposed for the catalytic reaction.

Influence of support on the performance of copper catalysts for the effective hydrogenation of ethylene carbonate to synthesize ethylene glycol and methanol

Hydrogenation of ethylene carbonate (EC) is an attractive and promising approach for indirect hydrogenation of CO2 to co-produce ethylene glycol (EG) and methanol (MeOH). In this work, thermodynamics of EC hydrogenation was firstly calculated, and the results disclosed that EC hydrogenation is exothermic (ΔrHθm = −71.59 kJ mol−1) and thermodynamically favorable (ΔrGθm = −25.62 kJ mol−1). The mesoporous silica supported copper catalysts were successfully prepared by facile ammonia evaporation method using KIT-6, MCM-41 and SBA-15 as support materials. The as-prepared Cu/KIT-6, Cu/MCM-41 and Cu/SBA-15 were thoroughly characterized by N2 physisorption, ICP-AES, N2O titration, FT-IR, XRD, H2-TPR, TEM, XPS and XAES. It was found that copper nanoparticles were well dispersed on these supports. Interestingly, a larger metallic Cu surface area with higher dispersion was obtained on SBA-15 when compared with KIT-6 and MCM-41. Furthermore, Cu0 and Cu+ species in various ratios were verified to co-exist on the surfaces of the three catalysts, which originated from CuO and copper phyllosilicate, respectively. The catalytic performances showed that Cu/SBA-15 exhibited a superior catalytic activity with a TON of 22.0 and 11.4 (mol mol−1) towards EG and MeOH, respectively. Importantly, 100% of EC conversion, 94.7% of EG yield and 62.3% of MeOH yield were achieved within a short reaction time of 4 h over Cu/SBA-15 under optimized conditions. The synergetic effect between Cu0 and Cu+ species, in which it was proposed that Cu0 species dissociated H2, while Cu+ species absorbed the carbonyl group of EC, was responsible for the higher catalytic activity of Cu/SBA-15.

Green and Practical Synthesis of Carbamates from Ureas and Organic Carbonates

Abstract A practical method for the synthesis of carbamates from ureas and organic carbonates was developed with 100% atom economy using La2O3/SiO2 as catalyst without any additional solvent. The scope of the protocol is demonstrated in the synthesis of 14 carbamates with various functional groups in excellent yields (76–95%).

Environmentally benign and effective syntheses of N-substituted carbamates via alcoholysis of disubstituted ureas over TiO2/SiO2 catalyst

Catalytic syntheses of cyclohexyl carbamates via alcoholysis of dicyclohexyl urea (DCU), which can be synthesized from CO2 and amines, were first investigated with low-molecular-weight alcohols, i.e., methanol, ethanol, butan-1-ol. TiO2/SiO2 catalyst was prepared by wet impregnation method using tetrabutyl titanate as titanium source. The catalyst was characterized by inductively coupled plasma/atomic emission spectroscopy (ICP/AES), N2 adsorption, X-ray diffraction (XRD), field emission/scanning electron microscopy (FE/SEM), transmission electron microscopy TEM), and NH3/temperature-programmed desorption (TPD) in detail. TiO2/SiO2 with 5 wt % loadings and calcination at 600 °C exhibited better catalytic activity, and excellent yields of >95 % with 98 % selectivities for desired carbamates were achieved. Accordingly, the strong acidity was considered to be responsible for its superior activity. Moreover, the catalytic activity can essentially be preserved during the recycling tests. The scope was also expanded to synthesize other alkyl or aryl carbamates via alcoholysis of the corresponding disubstituted ureas, and 94 % yields with 96 % selectivities can be achieved. It provided a good candidate for the organic carbamates syntheses via a phosgene/halogen-free and effective route.

Synthesis of hexamethylene-1,6-dicarbamate by methoxycarbonylation of 1,6-hexamethylene diamine with dimethyl carbonate over bulk and hybrid heteropoly acid catalyst

Synthesis of HDC by methoxycarbonylation of HDA with DMC was carried out over the bulk and hybrid heteropoly acid (HPA) catalyst. The catalysts were systematically characterized by XRD, FTIR, SEM and NH3-TPD techniques. The by-products produced in the reaction were identified and a possible reaction pathway was proposed based on the by-products analysis. The performances of bulk and hybrid HPA catalysts were evaluated. The H4[SiW12O40] catalyst revealed high performance compared with other catalysts and its high performance was attributed to its acidic properties. Effects of reaction parameters and reusability of the H4[SiW12O40] catalyst were also investigated. Under the optimized reaction conditions, HDA conversion reached 93.2% with 64.8% HDC selectivity and only 3.8% by-product selectivity. Moreover, a possible reaction mechanism was proposed for the synthesis of HDC over H4[SiW12O40] catalyst.

Facile Fabrication of Ultrasmall Copper Species Confined in Mesoporous Silica for Chemo‐Selective and Stable Hydrogenation Ethylene Carbonate Derived from CO2

The hydrogenation of ethylene carbonate to co‐produce commodity methanol and ethylene glycol has attracted growing interests due to the potential chemical utilization of CO2 in large scale. In this work, we report a novel and facile protocol for the preparation of mesoporous Cu@SiO2 catalysts and successfully applied the as‐synthesized catalysts in the hydrogenation of ethylene carbonate. The catalysts were characterized in detail by means of N2 physisorption, N2O titration, XRD, FT‐IR, H2‐TPR, TEM and XPS (XAES). This strategy is an effective method for fabricating the unique flower‐like mesoporous Cu@SiO2 with sub‐2.0 nm ultrasmall Cu particles. The results revealed that the involvement of β‐cyclodextrin improved the Cu dispersion and facilitated exposing more copper active sites, which also indicated that the confined catalyst inhibiting the sintering of copper particles. Meanwhile, the stability of the attained catalyst was superior with the modification of carbon. Importantly, among the catalysts tested in the hydrogenation of ethylene carbonate, 25Cu@SiO2‐β‐P with appropriate copper loading as well as moderate Cu+ ratio exhibited superior catalytic performance. Accordingly, the synergistic effect between the Cu+ and metallic Cu0 species was crucial for obtaining better catalytic activity.