Microemulsion Prepared By Ultra-fine Coated Catalyst And Its Catalytic Phenol Oxidative Carbonylation Reaction

The direct synthesis of diphenyl carbonate (DPC) by oxidative carbonylation of phenolwith CO and O₂ is a promising synthetic method because of its simple process, cheap raw material and no pollutants produced. In this paper, the effects of various conditions on the phase equilibrium of water-in-oil (W/O) microemulsion were systematically studied. The preparation of ultrafine embedded catalyst using W/O microemulsion as nano-reactor for synthesis of DPC was also studied. At last, the exploration of environmentally friendly solvent for oxidative carbonylation of phenol was carried out.The influences on the homogeneous region in W/O microemulsion were studied by utilizing the pseudo-triangle phase diagram. The homogeneous region in W/O microemulsion stabilized by the nonionic surfactant TX-10 is larger than that of the microemulsion stabilized by the cation surfactant, CTAB. When using TX-10 as surfactant and the weight ratio of m(S)/m(CS) equals to 1, the interface between water and oil is the most stable and can form the largest W/O microemulsion homogeneous region. As the increase of temperature, the area of W/O microemulsion region decreases evidently. The pH value of the water phase and the length of the carbon chain of the co-surfactant have a less effect on the stability of the W/O microemulsion. When the electrolyte solution was used as water phase, the area of W/O microemulsion homogeneous region decreased with the increase of its concentration.The conductivity of the W/O microemulsion increases with that of water phase at percolation threshold. It indicates that the take place of percolation is due to the connection of 'inner phase' in W/O microemulsion. However, the percolation doesn't exist at any situations. When the weight ratio of V(S+CS)/V(Oil) equals to 1, the maximum value of the conductivity is independent of the value of the water phase. It can be concluded that the connection of the 'inner phase' doesn't occur at this situation. The number of the water core in the microemulsion increases with the increase of the water content. They collide with each other and then leave away rapidly not to form the electric chain, so the percolation doesn't happen.Using PeakFit 4.12 data processing soft, the stretching vibration of hydroxyl group of water molecular in W/O microemulsion was multiple fitted to study its existing mode. There are three different kinds of water molecular and they are the trapped water, which are trapped in the long carbon chain of the surfactant; the free water, which are located in the center of the water core; the bounded water, which are bounded with the oxyethylene of TX-10 by hydrogen bond. But when the water content is low, there areonly two kinds of water molecular and the trapped water is disappear. It shows that the acting force between the trapped water is weak. The free water and bounded water have priorities to be come into being when the water is a little. Moreover, the molar fractions of the three kinds of water molecular don't change markedly with the increase of the water content in microemulsion.The size controllable mono-dispersed spherical silica particles were prepared in the W/O microemulsion composed of ammonia, cyclohexane, TX-10 and n-hexanol. The silica particles' sizes range from 50 to 90 nm and can keep stability at high temperatures. A novel method, W/O microemulsion coupling with sol-gel process, for the preparation of ordered mesoporous silica powder with large specific surface area was developed.A novel ultrafine embedded catalyst Pd-Cu-O/SiO2 was prepared using W/O microemulsion as nano reactor. XRD, TEM, SEM and XPS were used to characterize it. It shows that the active center of the catalyst is the complex oxide CuPdO2 which was wholly or partly embedded in the silica particles in nano scale. Because of the protection by silica, this catalyst has higher activity and longer service time than that of the catalyst prepared by impregnation or sol-gel process. The DPC yield can reach to 35.4% and the TOP (Turnover of frequency) on Pd atom is 20.1 mol DPC/mol Pd?h. The heterogeneous Cu( II) promoter can change the active species from PdO to CuPdO2, then change the chemical environment of Pd atom and make it easy for Pd atoms to transfer electron to Cu atoms around. The homogeneous Cu2+ can promote the change Pd(0) -? Pd( II) more effectively than the heterogeneous Cu( II) because all the Cu2+ in the system can take action. While, only the Cu( II) that enter into the crystal lattice of PdO to form the CuPdO2 can obtain electron from Pd(0).The silica embedded metal palladium catalysts Pd/SiO2 were prepared using W/O microemulsion as nano-reactor. The size of metal palladium particles can be controlled in the range of 8-30 nm. From the evaluation by the synthesis of DPC, the catalyst with small palladium particles has higher activity and selectivity because the little the palladium particles, the larger the surface area of it and it implies the more probability for the molecular of reactants to contact with the active center. The reaction mechanism of oxidative carbonylation over Pd/SiO2 catalyst is the multiple step electron transfer process. Firstly, the metal Pd is oxidized to bivalent Pd( II) by Cu2+, while Cu2+ changes into Cu+. Then Pd( II) combines with PhO- to obtain the PhO-Pd-O-, which can react with CO to form PhO-C(=O)-Pd-O-. Finally, PhO-C(=O)-Pd-O- reacts with the second PhO- to prepare the PhO-C(=O)-O-Ph (DPC) and Pd(II) is reduced to Pd(0) simultaneously to finish the catalytic cycle.