Preparation,characterization,and Catalytic Performances Of Cobalt Catalysts Supported On KIT-6 Silicas In Catalytic Oxidative Desulfurization

Sulfur-containing compounds in oils are harmful to the ecosystem whose cost-effective removal is still a challenge.Oxidative desulfurization?ODS?for oils has been paid close attention recently due to its moderate reaction conditions and low costs.Besides,ODS could effectively remove thiophenes and its derivatives.In this study,in order to produce ultra-low sulfur oils,dibenzothiophene?DBT?,as the most typical sulfur compound,was removed via oxidation-extraction desulfurization system.In this paper,novel heterogeneous catalysts of cobalt supported on KIT-6 mesoporous silicas were prepared and evaluated for oxidative desulfurization?ODS?under ambient conditions using cyclohexanone peroxide?CYHPO?as the oxidant.The model oil was obtained via dissolving DBT in the n-octane.The conventional wet impregnation method was applied for the preparation of the catalysts,and cobalt nitrate was used as the precursor.The catalysts were characterized by?X-ray diffraction?XRD,N₂-physisorption,?Fourier transform infrared?FT-IR,?Thermogravimetric Analysis?TGA,?Scanning Electron Microscopy?SEM/?transmission Electron Microscope?TEM and?X-ray Photoelectron spectroscopy?XPS.The data showed that the KIT-6 mesoporous silicas had a spherical matrix with smooth surface.And the cobalt metal has been successfully load in the carrier.The results help better explain the satisfactory catalytic performance.The catalytic activities of Co/KIT-6 catalyst in total oxidation of dibenzothiophene?DBT?were evaluated at various conditions.Co/KIT-6 catalysts showed high ODS activity due to Ia3d mesoporous structure resulting in better cobalt dispersion,higher activity of Co,and faster diffusion of reactant and products.In order to optimize catalytic oxidation desulfurization conditions,the effect of different variable parameters on the desulfurization efficiency,including reaction temperature,the concentration of CYHPO,the weight of catalyst Co/KIT-6 and the molar ratio of CYHPO/DBT were investigated.DBT conversion by this heterogeneous ODS system could reach 98.68%.The inhibitory effect of quinoline on ODS was higher than carbazole and indole,adding quinoline into model oil under same conditions led to a decrease of the conversion of DBT from 98.68%to 65.67%when the concentration of quinoline increased from 160 ppm to 4845 ppm.The higher the initial sulfur concentration in model oil,the higher the residual sulfur concentration,the more difficult for deep desulphurization.The Box-Behnken design was utilized to evaluate the effects of the main operating parameters,including oxidation temperature?40^?C¹30^?C?,catalyst amount?0.02⁰.25 g?and O/S?1.0⁸.0?on DBT removal.The optimum values were found to be 93^?C,0.16 g and 5.7,respectively.Removal rate of DBT maximized 99.36%.Statistical results also showed the degree of importance was:O/S>catalyst amount>oxidation temperature.Kinetics data correlated well with the pseudo-first-order equation.The apparent rate constants of 50 ppm sulfur,150 ppm sulfur and 400 ppm sulfur were 0.1959 min^-1,0.1407 min^-1,and 0.1096 min^-1.The activity of the desulfurization system was above 97.5%after regenerating for 7 times.These data showed that this novel Co/KIT-6 catalysis system has the potential to be applied in ODS from oils.