Study On The Direct Catalytic Benzene To Phenol

Recently, people have cared more about the environment and resource,especially,with the rapid development of Green Chemistry, people concern more and moreabout how to improve the atomic efficiency, and how to use catalyst to replace thetraditional reagent in chemical synthesis, in an attempt to eliminate environmentalpollution and to save resource.The direct catalytic hydroxylation of benzene tophenol using benzene as the raw material, needs only one step from benzene to thefinal product. This accords with the view point of Green Chemistry. This reaction isdirectly connected to the activation of C-H bond on aromatic ring. This is one ofthe most important subjects that deserve detailed investigation. In addition, it isalso one of the most difficult problems in synthetic chemistry. In order to realizethis goal, the design and preparation of effective catalysts are fatally important. Inthis thesis, the direct catalytic hydroxylation of benzene to phenol was studied. Twokinds of catalysts were prepared and characterized. The catalytic activity wasinvestigated and the reaction conditions were optimized. Two kinds ofheteropolyacids (HPAs) including vanadium-substituted silicomolybdenic andvanadium-substituted silicotungstic heteropolyacids were prepared using multi-stepmethod. The HPAs were characterized by elementary analysis, thermal gravimetricanalysis, infrared spectroscopy, UV-vis spectroscopy and X-ray powder diffractiontechniques. The results showed that the as-prepared compounds were HPAs withKeggin structure. The as-prepared HPAs were used as catalysts for the directhydroxylation of benzene in glacial acetic acid solvent with hydrogen peroxide asoxidant. The experiment showed that the two vanadium-containing HPAs had catalytic activity. This indicates that vanadium species in HPAs is the active phasefor the direct hydroxylation. Mo-containing HPA has higher catalytic activity ascompared with the W-containing HPA. In the present work, the turnover number ofmono-vanadium substituted silicomolybdenic catalyst was 26 mol phenol/molcatalyst with a yield of 17.2 % and a selectivity of 90.3 % to phenol. And a yield of4.3% and a selectivity of 87.4% for vanadium-substituted silicotungstic.The mono-vanadium substituted silicomolybdenic was supported onγ-Al₂O₃,NaX-zeolite, TiO₂, SiO₂ and coconut shell actived carbons. It is shown that all thesupported heteropolyacid catalysts are catalytically active in the directhydroxylation of benzene to phenol. The catalytic activity is closely related to thekinds of the supports, over one support, the more HPAs are supported, the higherthe catalytic activity. The amount of heteropolyacid supported is related to thesupporting procedure. The content supported obtained by reflux-adsorption isnearly two times higher than that obtained by inpregnation. Under the optimalexperimental conditions, the coconut shell actived carbons was found to possessthe best catalytic activity with a content of HPAs of 16.3 % supported and a yieldof 7.4 % to phenol.The activity the of catalysts keeps stable when repeatedly usedfar than 5 times.