A Study On Noble And Non-noble Metal Catalysts For Partial Hydrogenation Of Benzene To Cyclohexene

The partial hydrogenation of benzene to cyclohexene is not only has atom economy, but also has the characteristics of environmental friendliness. When studying the partial hydrogenation of benzene to cyclohexene catalyst, both in theoretical and applied research, has a very important significance. The main thesis of study is the preparation of the ZnO-supported Mo2N/Mo2C catalyst and Zr02-supported Ru-Zn catalyst, and the catalytic activity of the partial hydrogenation of benzene to cyclohexene. The main results or conclusion of this paper are as follows,(1) The thermal treatment of zinc oxide, HMT (glucose) and ammonium molybdate mixture at650-800℃for3h is employed to synthesize the ZnO-supported Mo2N/Mo2C catalyst under N2or H2atmosphere. In contrast to SiO2and Al2O3as the carrier reported in the previous literature, we found that ZnO can be reacted with the molybdenum precursor to form a Zn-Mo compound, which significantly affect the thermal treatment products. Under N2atmosphere, if there is no ZnO, the resulting product is γ-Mo2N, when the carrier is ZnO, the resulting product is Zn2Mo3Og. When thermal treatment is conducted in H2atmosphere, a new Zn-Mo compound whose XRD pattern is quite similar to that of Fe2MoO4serves as the intermediate. At a relatively low temperature (650-700℃), the new intermediates easier conversion the β-Mo2N catalyst, resulting β-Mo2N become the main component of the catalyst. Our results also indicate that as the heat treatment temperature of the rise, there is conducive to the formation of the catalyst as a main component to β-Mo2C. So we can control the ratio of β-Mo2N to β-Mo2C by proper choice of treatment temperature. According to the characterization results by XRD and TEM, at700℃, the β-Mo2C and β-Mo2N average grain size of the ZnO-supported β-Mo2N/β-Mo2C catalyst is about8.5and13.2nm, respectively.(2) Research with ZnO-supported β-Mo2N/β-Mo2C as benzene liquid-phase hydrogenation catalyst found that the catalyst without surface pretreatment, the presence of solvent (such as water, ethanol or ionic liquid [Emim] BF4), additives (such as different amount of Cu, Ni and P) and the change of the carrier (ZrO2take the place of ZnO) can change the liquid-phase hydrogenation catalyst activity, but can’t improved the selectivity of cyclohexene (its selectivity is zero). However, after dealing with the surface oxidation catalysts (in the air or NaOH aqueous solution at room temperature), can be detected the presence of cyclohexene in the product, and in2M NaOH treatment72h at room temperature, the selectivity of cyclohexene can reach about1%.(3) On the basis of Ru catalysts preparation at home and abroad, the first research of the hydrothermal one-step synthesize ZrO2-supported Ru-Zn catalysts, and compared with conventional preparation methods. The results show that, under the same conversion, hydrothermal conditions (temperature and time), Ru load and the quality ratio of Ru-Zn has obvious effect on the catalyst selectivity. Optimization of preparation conditions is:the load of Ru is4.8%, the content of zinc is3.7%, the hydrothermal treated under the condition of200℃for10h. The results also indicate that:Under the condition of the conversion rate remain basically unchanged, the hydrothermal one-step on the selectivity of cyclohexene is superior to conventional method for the preparation of catalyst, under the condition of the same evaluation, the selectivity of cyclohexene is12-18%higher by the hydrothermal one-step.