Preparation Of Co-Mo Catalyst Loaded Over Complex-support Using Urea Controlling Process And The Reaction Kinetics Study

The sulfur in diesel converts into SOX while burning, which is harmful to human being healthy and natural environment. The increasingly strict non-sulfur diesel regulations being implemented by the developed countries bring great challenge to refinery technology. A lot of industrial practice and researches showed that the improvement of catalyst is still the most efficient way to reach deep desulfurization. Nowadays, most industrial catalysts are prepared using traditional method, which is difficult to produce low sulfur diesel and the weak poison resistance shortened the catalyst lifetime while processing high sulfur content feed.The expensive price, difficulty in shaping and weak strength hindered the industrialization scale up of TiO2 supported hydrodesulfurization catalyst or the bulk catalysts.In this work, our aim is to promote the hydrodesulfurization (HDS) catalyst activity from two aspects. Firstly, new Urea Matrix Combustion (UMxC) method and Urea Chelating Agent method (UCA) were used to optimize the active phase dispersion exploiting the controllable function of urea during the preparation. Secondly, the catalyst support is modified by adding TiO2 or MgO using the novel method. The surface properties and morphology were characterized using XRD, LRS, HRTEM, XPS,N2 physorption, FT-IR and TPR technologies.The HDS catalytic activity was tested in a stainless fixed-bed reactor(600mm long,Φ40mm×10mm).The xylene solution of B, BT and (or) DBT was used as the model compound, the 3% CS2 cyclohexane was used as the presulfur agent. Effects of preparation method, support component and reaction conditions on HDS catalytic activity were discussed corresponding to the HDS mechanism. The HDS reaction kinetics of BT and DBT were studied.It showed that the UMxC method had the characters of saving time, simple steps and avoiding the damage of catalyst crystal morphology. The catalyst presented uniform pores, higher pore volume and better dispersion, especially without forming nonactiveβ-CoMoO4 and twins crystal structure compared with that of co-impregnaition method.The HDS activity of Co-Mo/Al2O3 catalyst prepared using UMxC method was about 10% higher than that of prepared using sequential impregnation (SI) and co-impregnaition (CI) methods.Compared with Co-Mo/Al2O3 catalyst, the addition of TiO2 changed the electronic states of catalyst surface and the Lc/La of multi-layer crystal increased, benefited forming more high active Co-Mo-S andMoS2 phase. Proper addition of TiO2 favors improving catalytic activity, especially increasing the removal of DBT.The HDS tests showed that the reaction temperature, LHSV and catalytic component notably affected the removal of DBT. The Co-Mo/Al2O3-TiO2 (UMxC) catalyst with 20% TiO2 addition content and 0.3～0.5 Co/Mo(mole ratio) presented the best removal ratio of the three sulfur compounds at:300-360℃,3～6 h-1 LHSV.Co-Mo/Al2O3-TiO2 catalysts prepared using UCA method had the character of smaller average pore diameter, mono-layer and multi-layer crystal morphology, bigger layer space which may be beneficial to the connection of big molecular DBT with active component. The addition sequence and content of urea resulted in different crystal and pore morphology. The activity of Co-Mo/Al2O3-TiO2 catalyst prepared using UCA method was lower than that of UMxC method, although the catalysts prepared using the two methods both presented high catalytic activity.The results of Co-Mo/Al2O3-MgO catalyst prepared using UCA method showed that MgO greatly affected the morphology of catalyst compared with Al2O3 mono-support. With the rising of MgO content, the reduction temperature of Mo-oxide increased, Co-O-Mo cluster raising, more metal component existed as small clusters on the surface of catalyst forming more unsaturated sites, thus benefited forming more and higher active Co-Mo-S phase after sulfurization. The decrease of residual carbon peak meant the trend of lower accumulation of carbon. The HDS reaction results showed that Co-Mo/Al2O3-MgO catalyst presented higher activity at low H2/HC ratio (300) compared with Co-Mo/Al2O3-TiO2 catalyst.The addition amount and sequence of urea affected the catalyst morphology significantly during the preparation. The control function of urea on catalyst textural properties and crystal morphology was expected. The Co-Mo/Al2O3-TiO2 (UMxC) catalyst presented higher average pore diameter, uniform dispersion and multi-layer crystal morphology and high HDS activity. The HDS reaction kinetics data of 40～60 mesh Co-Mo/Al2O3-TiO2 (UMxC) catalyst gained by the elimination of inner-diffusion, the direct HDS reaction of BT and DBT hyperbolic type kinetics models were:The parameters in the above kinetics models were as following: k2...