The condensation reaction between methyl N-phenylcarbamate (MPC) and HCHO to form methylene diphenyl-4,4′-dicarbamate (MDC) over different solid acid catalyst was studied. The results showed that the catalysts with surface Lewis acid sites having higher acid strength favored MDC synthesis. Among the solid acid catalysts, Hβ exhibited good catalytic activity for MPC condensation. Solvents also had an effect on the catalytic activity; protic solvents, methanol, or H2O, were detrimental, while dimethyl carbonate (DMC) was found to be the most appropriate reaction medium. The optimal reaction conditions consist of a reaction temperature of 160 °C, a reaction time of 3 h, n(DMC)/n(MPC)/n(HCHO)of 50:1:0.25 and 0.6 g/30 mL DMC catalyst amounts. Under these conditions, the MPC conversion is 37.2%, and the MDC yield (based on HCHO) is 76.4%. The Hβ catalyst could be easily regenerated by calcination, and no significant loss in catalytic activity was observed after five repeat uses.

Zn(OAc)2 is known to exhibit excellent catalytic activity for aromatic carbamate synthesis by the reaction of aromatic amine and dimethyl carbonate (DMC). It is determined that an induction period exists during the synthesis of dimethyl-4,4′-methylenediphenyl dicarbamate (MDC) and methyl N-phenyl carbamate (MPC), although this period is more evident in the case of MDC. Zn(OAc)2 is able to catalyze the reaction of amine and DMC, but also react with DMC to form Zn4O(OAc)6, which also shows excellent catalytic activity for carbamate synthesis. As for MDC synthesis, Zn4O(OAc)6 plays the important role. However, Zn(OAc)2 plays the leading role in MPC synthesis. The deactivation of Zn4O(OAc)6 was also investigated. Zn4O(OAc)6 was initially transformed into Zn5(OH)8(OAc)2·2H2O (LHZA) and then into ZnO.

SO3H-functionalized imidazole ionic liquids [HSO3-bmim]CF3SO3, [HSO3-bmim]-HSO4, [HSO3-bmim]CH3SO3 and [HSO3-bmim]p-CH3(C6H4)SO3H were used as catalysts for the hydration of cyclohexene to cyclohexanol. It was found that the catalytic activity of the ionic liquids increased with increasing acid strength, and [HSO3-bmim]HSO4 simultaneously showed high activity and high cyclohexanol selectivity. Under the optimized conditions, cyclohexene conversion was 10.1 % with 98.7 % cyclohexanol selectivity. When [HSO3bmim]HSO4 was separated and reused for the fifth time, cyclohexene conversion was still 10.2 % with 99.0 % cyclohexanol selectivity. The good stability may be attributed to the little effect of the side-products with high-boiling points on the ionic liquid.

•Zn(OAc)2/SiO2 was prepared by incipient impregnation.•Zn(OAc)2/SiO2 shows the similar catalytic performance as Zn(OAc)2.•The stability of Zn(OAc)2/SiO2 improves considerably, but Zn(OAc)2 cannot be reused.•The cause for the improved stability of Zn(OAc)2/SiO2 was investigated.Zn(OAc)2 was found to give excellent catalytic performance for methyl N-phenyl carbamate (MPC) synthesis from aniline and dimethyl carbonate (DMC). However, after being used for only once it tended to lose activity because of the formation of ZnO by the reaction of Zn(OAc)2 and methanol. Zn(OAc)2/SiO2 was prepared by incipient impregnation and it gave excellent catalytic performance in MPC synthesis, on which aniline conversion and MPC yield were 98.1% and 93.8%, respectively. And Zn(OAc)2/SiO2 was found to be more stable than Zn(OAc)2 during the reaction. When Zn(OAc)2/SiO2 was used for the fifth time, aniline conversion and MPC yield were found to be 64.3% and 38.1%, respectively. The Zn(OAc)2/SiO2 catalyst was characterized by TG-DTA, ICP, FTIR, XRD and XPS. The characterization results suggested that the deactivation of Zn(OAc)2/SiO2 was also due to the formation of ZnO and there were two reasons for the improved stability of Zn(OAc)2/SiO2 catalyst. One was the formation of the Si–O–Zn bonds in Zn(OAc)2/SiO2 catalyst, which increased the steric hindrance of Zn and consequently retarded the reaction between Zn(OAc)2 and methanol. The other cause was the dehydration between methanol and the hydroxyl group on the SiO2 surface, which reduced the chance of a reaction between methanol and Zn(OAc)2.Download high-res image (71KB)Download full-size image

Ru–Zn/SiO2 catalysts were prepared in a water-in-oil microemulsion for partial hydrogenation of benzene. Hydrazine hydrate was added during the preparation to obtain Ru particles with controllable size. The results indicated that, the addition of hydrazine hydrate led to Ru particles with larger size, and the amount of hydrazine hydrate did not show obvious influence on the size of Ru particles. However, the catalytic activity changed significantly with addition of hydrazine hydrate, even if the Ru particle size, obtained by Scherrer equation, remained constant. This is attributed to the formation of a highly dispersed Ru species and crystalline Ru simultaneously. The former favored benzene conversion, and the latter was beneficial for increasing cyclohexene selectivity by contrast.