Synthesis Over Rare Earth Modified Cr/Al₂O₃ Catalysts And Kinetics Studies Of The Direct Hydroxylation Of Benzene To Phenol

Phenol is an important chemical raw materials, it has a high application value. More than 92% phenol has been produced by the cumene process. However, this process consists of multi-step reaction, having many by-product and environment pollution. Since the 20th century, with the shortage of resources and the development of green chemistry, people want to conserve resources and reduce environmental pollution. So in recent years, one-step oxidation of benzene to phenol is a hot topic. To achieve this goal, the most critical factor is the selection and preparation of the catalyst.M/Al2O3 catalyst was synthesized with aluminum isopropoxide as aluminum source, glucose as template, under acidic conditions of use the in situ sol-gel method. The prepared catalysts were characterized by XRD, BET, TQand TEM. The results show that the loaded transition metals of the framework of mesoporous aluminum oxide of more stable structure and a narrow pore sizes distribution than the pure aluminum oxide. The reaction parameters include time, temperature, solvent, molar ratio of recatants and catalyst amount were also investigated in detail. The results show that C6H6/H2O2(molar ratio)=1:3, reaction media is acetonitrile, temperature 60℃, reaction time 4h, catalyst amount 0.05g. The results showed that M/Al2O3 catalytic materials with the good catalytic activity, but also showed that the catalytic activity center is the transition metals of the mesporous materials.Six transition metals were introduced into the framework of mesoporous aluminum oxide was to perparaed of M/Al2O3 catalyst. Through the compared the activity, Cr/Al2O3 was chosen as the best active catalysts. And nine kind of rare-earth metals(La,Pr,Nd,Eu,Er,Sm,Gd,Yb,Ce)were introduced into the modified Cr/Al2O3 catalysts.The results showed that the activity of catalysts are enhanced when rare-earth metals introduced into the catalyst. And the Nd-Cr/Al2O3 revealed the best catalytic activity. Thus the kinetics of the direct hydroxylation of benzene to phenol using neodymium doped Cr/Al2O3 as catalyst and H2O2 as oxidant was invetigated by means of ultraviolet spectroscop. It was found that the hydroxylation rate of benzene to phenol indicated first-order dependence with respect to the substrate, to the catalyst and to the oxidant, respectively. The activation energy of the reaction was evaluated to be 24.41kJ/mol. The process and corresponding mathematic model for the kinetics of the reaction were proposed.