Catalytic Conversion Of Carbon Dioxide To Several Chemicals

In recent years, the concentration of carbon dioxide(CO2) in the atmosphere is sharply rising with the consumption of traditional sources. In fact, CO2 is not only the main greenhouse effect but also the most abundant and broadest carborn resource distributied in the world. CO2 can be converted to useful chemicals, which is consistent with the requirement of green chemistry in terms of utilization and environmental protection. In this work, N, N’-dibutylurea(DBU), methyl N-phenyl carbamate(MPC) and diphenyl carbonate(DPC) were synthesized by using CO2 as carbon resource.The synthesis of DBU from CO2 and butylamine in the presence of caesium hydroxide(CsOH) was investigated first. The yield of DBU was quantitatively determined by gas chromatograph(GC), and the objective product was further characterized by infrared spectroscopy(IR), mass spectrometer(MS) and1hydrogen-nuclear magnetic resonance(1H-NMR). The effect of catalyst, solvent,reaction time, reaction temperature and pressure on the synthesis of DBU was also investigated. Yield of 91.8% and selectivity of 98.0% towards DBU were obtained at170 oC and 8 MPa for 10 h with a 0.1 molar ratio of CsOH to butylamine using acetonitrile as solvent. The products in the reaction mixture were identified by gas chromatograph mass spectrometer(GC-MS) and a possible mechanism for the synthesis of DBU from CO2 was proposed.The synthesis of MPC from CO2, aniline and CH3 OH in the presence of cerium dioxide(CeO2) was also studied. The results showed that the catalytic performance of CeO2 was significantly improved by the addition of n-butyllithium(BuLi). 9.4% yield of MPC was obtained at 170 oC and 12 h under 5 MPa of CO2 initial pressure with0.3:1:1.5:225 molar ratio of CeO2, BuLi, aniline and CH3 OH. Several possible pathways for the synthesis of MPC from CO2, aniline and CH3 OH were futher investigated based on the previous researches. The reaction mixtures were qulitatively analyzed by GC-MS, and the formation of phenyl isocyanate(PI) and MPC were identified. PI was suggested to be the possible intermediate, and a possible mechanism for the synthesis of MPC from CO2, aniline and CH3 OH was proposed.Fe3O4@SiO2-ZnBr2 was prepared by supported ZnBr2 on the composite oxide support of Fe3O4@SiO2 which was obtained from Fe3O4 nanoparticles and tetraethyl orthosilicate, The supported catalyst was further characterized by IR, X-ray diffraction(XRD), X-ray photoelectron spectrometer(XPS) and BET method. Andthe loading of Zn was determined by atomic absorption spectrometry(AAS). The results of IR and XPS indicated that there were a large number of accessible hydroxyl groups(-OHs) on the surface of Fe3O4@SiO2-ZnBr2. The XPS characterization also revealed that there was a synergistic effect between ZnBr2 and –OHs, giving a complex which may contribute to the excellent catalytic performance of Fe3O4@SiO2-ZnBr2. The catalytic performance of Fe3O4@SiO2-ZnBr2 for the synthesis of DPC from CO2, phenol and carbon tetrachloride(CCl4) was studied.28.1% yield of DPC was obtained at 130 oC and 8 MPa for 4 h with 0.1:1 molar ratio of ZnBr2 to phenol in the presence of 15.1 wt% Zn loading. Fe3O4@SiO2-ZnBr2 was recovered and its recyclable catalytic performance was investigated, The results showed that the catalytic actively of Fe3O4@Si O2-ZnBr2 almost remained constant during the first four cycles. In addition, the products in the reaction mixture were identified by GC-MS analysis which confirmed that the synthesis of DPC is accompanied by the formation of phenyl salicylate, a possible mechanism was then proposed.