Catalysts And Catalysis Of The Direct Oxidation Of Benzene To Phenol

Phenol is an important chemical intermediates for many industrial products, such as agricultural chemicals, petrochemicals and plastics. Phenol was synthesized by the traditional process. The traditional process of phenol synthesis is cumbersome. And by-product influences environment. So the traditional process of multi-step synthesis of phenol gradually develops into single-step process. Single-step process of phenol synthesis has become one of focus between scientific point of view and the importance of phenol in the industry. In order to achieve one-step synthesis of phenol, the focus of many studies is used to search for a new type of catalyst and oxidant.This paper is divided into two parts. First, Cr/γ-Al2O3catalyst was synthesized by sol-gel method with introducing chromic nitrate under calcined. Direct hydroxylation of benzene to phenol was accomplished by Cr/γ-Al2O3catalyst. The reaction factors of direct hydroxylation of benzene to phenol were studied in detail. The best reaction conditions are picked up. Rare-earth was introduced into Cr/γ-Al2O3catalyst to form Nd-Cr/γ-Al2O3. Nd-Cr/γ-Al2O3catalyst was used for direct hydroxylation of benzene to phenol. The results show catalytic activity of Nd-Cr/γ-Al2O3catalyst is higher than Cr/γ-Al2O3catalyst. Crystalline phase, specific surface area and surface acidity of Nd-Cr/γ-Al2O3catalyst were studied by XRD, BET, TEM and NH3-TPD. The results show neodymium oxide can improve the specific surface area of supporter. Cr/γ-Al2O3and Nd-Cr/γ-Al2O3were characterized by XPS,27Al MAS NMR and DRS-UV-vis. The valence state of chromium in Cr/γ-Al2O3and Nd-Cr/γ-Al2O3were different, because the valence state of chromium was changed by neodymium metal oxide. The valence state of chromium has be changed from+6to+3by Nd. Neodymium can assist to improve the catalytic activity. Chromium is the major catalytic component in Nd-Cr/γ-Al2O3. The role of Neodymium oxide is to change the valence state of chromium in the catalyst and to assist to improve the catalytic activity.Second, γ-Al2O3was synthesized by dynamic hydrothermal synthesis method. The reaction parameters such as types of surfactant and temperature were also investigated in detail, and to determine the optimal preparation conditions. In the best preparation conditions, chromium nitrate and neodymium nitrate were loaded in the supporter, and then calcined to form Cr/γ-Al2O3and Nd-Cr/γ-Al2O3catalyst. Content of chromium and neodymium towards influencing of phenol yield was studied. The results showed catalytic activity of catalysts prepared by the sol-gel method were higher than dynamic hydrothermal synthesis method. NH3-TPD results show that the metal oxide in the catalysts can reduce the surface acidity of γ-Al2O3, the yield of phenol has obviously improved. The results indicate that the surface acidity of the carrier have a significant effect towards the oxidation of benzene to phenol, reducing the surface acidity can increase the catalytic activity. Nitrogen adsorption and desorption isotherms of the catalyst indicate specific surface area of catalyst prepared by dynamic hydrothermal synthesis method were less than the sol-gel method.