Highly Selectively Catalytic Hydroxylation Of Benzene

Phenol is an important chemical in industry, as an intermediate for biphenol A, phenol-aldehyde resins, nylon-6, etc. It's mainly produced by cumene peroxidation process, which requires three steps of reactions and is limited by the market requirement of equimolar byproduct acetone. Because it needs many kinds of acid and organic reagents, cumene peroxidation process brings the problems of wasting materials and environment pollution. For economical and ecological environment reasons, the one-step direct hydroxylation of benzene with cleaner and cheaper oxidants becomes one of the most exciting challenges of catalytic chemistry.In this dissertation, we studied the one-step hydroxylation of benzene to form phenol with an environmentally safer and cheaper oxidant, molecular oxygen. Several heterogeneous catalysts were designed and thus synthesized for benzene hydroxylation using molecular oxygen in presence of ascorbic acid. These catalysts performed highly catalytic activation and nearly 100% phenol selectivity was obtained in all the cases. Therefore, this catalytic process is environmentally benign, which may be a prospective chemical process in industry.Iron and vanadium substituted SBA-15 was synthesized to catalyze hydroxylation reaction of benzene. Well ordered hexagonal arrays of 1D mesoporous channels and 2D P6mm hexagonal structure was confirmed by XRD, TEM, N₂ adsorption-desorption and the existing of highly dispersive tetrahedral coordinated Fe and V species were proved by ESR and UV-vis spectrum. This material possessed highly catalytic activity for benzene hydroxylation using molecular oxygen as oxidant. The yield and the selectivity of phenol were obtained of 14.5% and 100%, respectively.The VOx/CuSBA-15 catalyst was synthesized to catalyze hydroxylation of benzene. A high yield of phenol was achieved at 27% with the selectivity of nearly 100%. The VOx/CuSBA-15 possessed two specialties: (1) it selectively catalytically activated dioxygen molecules rather than H₂O₂, (2) it selectively catalyzed benzene hydroxylation to form phenol, but phenol could hardly react under certain reaction condition. Both copper and vanadium oxide supported catalyst had a prominently catalytic performance toward the benzene hydroxylation comparing to other bi-transition metal oxides or monometallic supported catalysts, which suggested there might be a cooperation between copper and vanadium oxide on the support. It is believed that benzene hydroxylation over V0x/CuSBA-15 catalyst occured through the hydroxyl radical pathway without the participation of H₂O₂, and catalytic activation of molecular oxygen to form hydroxyl radical would be a rate determingstep.Three complex catalysts were studied for benzene hydroxylation. The benzene conversion and phenol selectivity were obtained of 18.8% and 100%, respectively, over [Fe^II(edta)] catalyst using molecular oxygen as an oxidant. VO(phen) performed very high catalytic activation toward benzene hydroxylation, over which benzene conversion and phenol selectivity were obtained of 20.8% and 99.0%, respectively. The metallophthalocyanines were the most prospective catalysts. Although the benzene conversions were not higher than 13%, the metallophthalocyanines did not dissolve in the reaction solution and the catalytic activation did not decrease after being reused 3 times.Heteropoly acid nanoparticles were successfully assembled by the novel vacuum impregnation method. High vacuum (10^-7Torr) pretreatment was applied for clearing water molecules, nitrogen and other contaminations from the pores of the SBA-15 in order to provide more capacity and to finish crystallization of heteropoly acid at relatively low temperature. Highly pure Keggin structural heteropoly acid nanoparticles with diameter around 20nm both inside and outside the pores of SBA-15 were obtained.Another novel method was developed to get heteropoly acid nanocrystals controlled directionally self-assembled in large-pore SBA-15 successfully, in which the chemical reaction of hydrolysis was used as main driving force for transportation of the guest. The utilization of the large-pore SBA-15 as a host, the method of high vacuum (10^-7Torr) and the water saturated channels of SBA-15 ensure that the number of heteropoly acid molecules incorporated in the pores would be plenty enough for the formation of nanoparticles. The selection of an appropriate extraction solvent guaranteed the higher purity of heteropoly acid nanoparticles within the channels of mesoporous silica SBA-15. Through this method, highly pure Keggin structural heteropoly acid nanoparticles with diameter around 20nm inside the channels of SBA-15 were obtained.The nano-heteropoly compounds possessed highly catalytic activation toward benzene hydroxylation using molecular oxygen as an oxidant. Phenol yield of 16.2% was obtained over nano-molybdovanadophosphoric acid, which was 3 times of that over bulk molybdovanadophosphoric acid. The MnPMo₁₀V₂/SBA-15 catalyst promoted the phenol yield to 18.1% with the selectivity of 100%. The catalytic activation was much higher than the reported heteropoly compounds.