The Studies Of Surface Properties On Carbide And Phosphide Catalysts For Hydrodesulfurization

Transition metal carbides and phosphides have shown superior activities in deep hydrodesulfurization(HDS)of transportation fuels.Catalytic activity is closely related to surface characters.However,there are only a few researches on surface properties of these catalysts supported on mesoporous molecular sieves(MMSs).So,the studies of surface properties on MMSs-supported catalysts are of great significance in the recognization of the sites available on these catalysts for the HDS process.In this thesis,the supported tungsten carbide,nickel and tungsten bimetallic carbide,nickel phosphide,nickel and cobalt bimetallic phosphide catalysts were prepared using MCM-41,MCM-48,SBA- 15 and SBA- 16 as supports.The structure of the samples was characterized by XRD,BET, NH₃-TPD and FTIR.All catalysts were evaluated by thiophene HDS.Finally, the adsorption of CO probe molecule was studied on both carbide and phosphide catalysts supported on MMSs by in situ diffuse reflectance FTIR spectroscopy(DRIFTS)analysis. For all tungsten monometallic carbide catalysts,W_xC_SBA-16 has the best HDS catalytic activity.The catalytic activity for thiophene HDS improved obviously after Ni addition,and the catalyst with Ni/W=0.75 has the best activity.The physical adsorption of CO on OH groups of catalyst surface was the strongest when Ni/W =0.75,suggesting that the more OH groups on catalyst surface,the better the HDS catalytic activity.In nickel phosphide catalysts,the nickel phosphide species was Ni₂P,and all samples still maintained well mesoporous structure.The conversion of thiophene HDS enhanced with the increase of reaction temperature as well as Ni or Co contents.The adsorption of CO on nickel phosphide catalysts observed at 2080-2075 cm^-1was attributed to CO terminally bonded to cus Ni^δ+(0＜δ＜1)sites.The intensity of this adsorption increased with Ni or Co contents increasing.The results indicated that Ni^δ+(0＜6＜1)sites were the effective active sites in HDS reaction.