A Cr/SBA-16 catalyst was prepared using Cr（NO3）3 as a precursor and mesoporous silica SBA-16 as a support via a simple impregnation method. The catalyst was characterized using wide-angle X-ray diffraction （XRD）, ...A Cr/SBA-16 catalyst was prepared using Cr（NO3）3 as a precursor and mesoporous silica SBA-16 as a support via a simple impregnation method. The catalyst was characterized using wide-angle X-ray diffraction （XRD）, low-angle XRD, N2 adsorption-desorption, transmission electron microscopy, and ultraviolet-visible spectroscopy. The catalyst activity was investigated in the direct bydroxylation of benzene to phenol using H2O2 as the oxidant. Various operating variables, namely reaction temperature, reaction time, amount of H2O2, and catalyst dosage, were optimized using central composite design combined with response surface methodology （RSM）. The results showed that the correla- tion between the independent parameters and phenol yield was represented by a second-order polynomial model. The high correlation coefficient （R2）, i.e., 0.985, showed that the data predicted using RSM were in good agreement with the experimental results. The optimization results also showed that high selectivity for phenol was achieved at the optimized values of the operating variables： reaction temperature 324 K, reaction time 8 h, H2O2 content 3.28 mL, and catalyst dosage 0.09 g. This study showed that RSM was a reliable method for optimizing process variables for benzene hydroxylation to phenol.展开更多
The main cause to the deactivation of ZSM-5 catalyst, used for oxidation of benzene to phenol (BTOP) by nitrous oxide, is that the carbon deposition on the catalyst surface blocks the mouth of pores of the catalyst.In...The main cause to the deactivation of ZSM-5 catalyst, used for oxidation of benzene to phenol (BTOP) by nitrous oxide, is that the carbon deposition on the catalyst surface blocks the mouth of pores of the catalyst.In the experiments, ZSM-5 catalyst was modified by chemical surface deposition of silicon, and then the effect of modification condition on the catalyst activation was studied. The catalyst samples were characterized by XRF,EPS, XRD, TEM, N2 adsorption at low temperature, pyridine adsorption-infrared technique and etc. All the above results show that the uniform SiO2 membrane can be formed on ZSM-5 crystal surface. The SiO2 membrane covers the acid centers on ZSM-5 surface to inhibit surface coking, to avoid or decrease the possibility of ZSM-5 pore blockage so that the catalyst activity and stability can be improved efficiently. The optimum siliconiting conditions determined by the experiments are as follows: 4% load of silanizing agent, volume (ml)/mass (g) ratio of hexane/ZSM-5=15/1, and 16 h of modification time. Compared with the samples without siliconiting treatment,the samples treated under the above optimum condition can increase the productivity of phenol by 14% for 3 h reaction time and by 41% for 6 h reaction time respectively.展开更多
基金the University of Tehran for financial support of this work
文摘A Cr/SBA-16 catalyst was prepared using Cr（NO3）3 as a precursor and mesoporous silica SBA-16 as a support via a simple impregnation method. The catalyst was characterized using wide-angle X-ray diffraction （XRD）, low-angle XRD, N2 adsorption-desorption, transmission electron microscopy, and ultraviolet-visible spectroscopy. The catalyst activity was investigated in the direct bydroxylation of benzene to phenol using H2O2 as the oxidant. Various operating variables, namely reaction temperature, reaction time, amount of H2O2, and catalyst dosage, were optimized using central composite design combined with response surface methodology （RSM）. The results showed that the correla- tion between the independent parameters and phenol yield was represented by a second-order polynomial model. The high correlation coefficient （R2）, i.e., 0.985, showed that the data predicted using RSM were in good agreement with the experimental results. The optimization results also showed that high selectivity for phenol was achieved at the optimized values of the operating variables： reaction temperature 324 K, reaction time 8 h, H2O2 content 3.28 mL, and catalyst dosage 0.09 g. This study showed that RSM was a reliable method for optimizing process variables for benzene hydroxylation to phenol.
文摘The main cause to the deactivation of ZSM-5 catalyst, used for oxidation of benzene to phenol (BTOP) by nitrous oxide, is that the carbon deposition on the catalyst surface blocks the mouth of pores of the catalyst.In the experiments, ZSM-5 catalyst was modified by chemical surface deposition of silicon, and then the effect of modification condition on the catalyst activation was studied. The catalyst samples were characterized by XRF,EPS, XRD, TEM, N2 adsorption at low temperature, pyridine adsorption-infrared technique and etc. All the above results show that the uniform SiO2 membrane can be formed on ZSM-5 crystal surface. The SiO2 membrane covers the acid centers on ZSM-5 surface to inhibit surface coking, to avoid or decrease the possibility of ZSM-5 pore blockage so that the catalyst activity and stability can be improved efficiently. The optimum siliconiting conditions determined by the experiments are as follows: 4% load of silanizing agent, volume (ml)/mass (g) ratio of hexane/ZSM-5=15/1, and 16 h of modification time. Compared with the samples without siliconiting treatment,the samples treated under the above optimum condition can increase the productivity of phenol by 14% for 3 h reaction time and by 41% for 6 h reaction time respectively.
