Direct Catalytic Oxidation Of Benzene To Phenol Over Ni-based Catalyst

The activities of a series of Ni containing catalysts were studied under mild conditions. The phase composition, reducibility and surface structure of the catalysts were investigated by using X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) techniques.Different support materials were used to prepare the catalysts, it was observed that these catalysts show different activities. When y -Al2O3 is used as support, the catalyst shows the highest activity, then molecular sieve, TiO2, activated carbon and SiO2 in a decreasing order.A series of Ni containing gamma-Al2O3 catalysts promoted by other three components were prepared and used in the direct oxidation of benzene to phenol. The results show that the catalyst with Ni loading up to 3wt% has the highest activity. Several parameters, such as the amount of catalyst used, the amount of ammonia, the amount of benzene, the amount of hydrogen peroxide and the concentration of ammonia also affect the performance of the catalyst.The additions of Ce, Ca or Pt on Ni3/gamma -Al2O3 catalyst does not enhance the catalytic performance of the samples for the target reaction, and a remarkable decrease in activity was observed. The used Ni3/ gamma -Al2O3 catalyst could be regenerated by H2 reduction.XRD, TPR and XPS characterizations indicate that the active phase for the target reaction may be originated from highly dispersed nickel oxide, while the presence of crystallites nickel oxides or nickel metal may reduce the activity. Theaddition of Ce, Ca or Pt may result in a decrease of nickel loading and the dispersion state of nickel, and then reduce the activity and stability of the catalyst. For different supports used, TPR profiles show that the catalysts with well-dispersed nickel oxide species and reducible at low temperature show high activity.L25(56) orthogonal design was used to optimize the experimental parameters for the direct hydroxylation of benzene by hydrogen peroxide over Ni3/gamma-Al2O3 catalyst. The six factors chosen for test are as the following, the reaction time, the amount of ammonia used, the amount of hydrogen peroxide used, reaction temperature, the amount of catalyst and benzene used, each with five levels. The result of the experiment carried out using the optimized conditions confirms that orthogonal design is really a perfect one for optimality catalyzed reaction conditions (reaction temperature 40,reaction time 4.5 hour, ammonia 50 ml, benzene 25 ml, H2O2 10 ml, catalyst Ig).Finally, we speculates the possible reaction mechanism as follows:...