Preparation And Hydrogenation Performance Of Layered Presulfur-free Catalysts

Current concerns about environmental conservation are imposing increasingly stricter legislation on the quality of petroleum-derived fuels.Hydrotreating processes are considered as some of the most cost-effective routes to remove sulfur and aromatics from diesel.Utilization of more active catalysts,because of their much lower investment costs,may be the most attractive solution for petroleum refiners.Prior to using,catalysts must be sulfided with a sulfurizing agent under high temperature and pressure to convert inactive oxides into sulfides.Unfortunately,the complete sulfidation of metal oxides is-hard to be achieved under the industry acceptable sulfidation temperature,leading to the less active sites and hence poor hydrotreating activity in deep hydrodesulfurization(HDS)of refractory dibenzothiophenes(DBTs)in diesel.Therefore,by virtue of the anion exchange ability of LDHs,thiomolybdate can be introduced into the interlayer of NiAl LDHs,which could be further calcined to prepare pre-sulfided hydrotreating catalysts.It may combine the advantages of LDHs and thiomolybdate,for instance,one-step synthesis of NiMo pre-sulfided catalysts without subsequent impregnation of molybdenum and nickel as well as activation in each step,highly dispersed active metals on catalysts.The effects of activation atmosphere and temperature,Ni/Mo ratios on the structure and properties of the pre-sulfided catalysts were studied.Then the pre-sulfided catalysts were used to evaluate dibenzothiophene(DBT)HDS activity and tetralin(THN)hydrodearomatization(HDA)activity.The results were listed as follows.1.Thiomolybdate was successfully intercalated into the interlayer of NiAl LDHs by the ion exchange method.The detailed investigations of preparative parameters such as reaction temperature,ion exchange time and starting solution pH on the crystallinity and purity of ion exchange products were studied.It is found that prepared at the ambient temperature,exchange time 24 h and pH 8.0 could obtain well crystallized and fully exchan ged thiomolybdate intercalated NiAl LDHs.2.Thiomolybdate intercalated NiAl LDH was calcined under N2 at different temperatures as pre-sulfided hydrotreating catalysts.Their properties and activity are governed by the calcination temperature.After calcination at 300?,poorly crystallized MoS2 and NiS2 are formed.It causes more CUS and better nickel promotion effects,resulting in higher DBT HDS activity.However,the further increasing calcination temperature leads to the transformation from NiS2 to NiS and Ni3S2 as well as the conversion from MoS2 to MoO2,resulting in the poorer HDS activity.The HDS activity and efficiency of the pre-sulfided catalyst calcined at 300? are higher than those of an oxidic catalyst derived from a molybdate intercalated NiAl LDH.Moreover,the THN hydrogenation activity of this pre-sulfided catalyst is 2.3 times higher than that of the oxidic catalyst,probably owing to CUS and non-stoichiometric sulfur species bonded on the catalyst surface.3.The HDS and HDA activity is related to the Ni/Mo molar ratios.Decreasing the Ni concentration leads to a significant generation of more active hydrogenation active sites resulting in an increase of the HDS activity of DBT and HDA activity of THN.With the increase of Ni/Mo ratio,the amount of NiS2 is increased,thus resulting in less promoting effect.Compared with the unsupported pre-sulfided catalyst,catalyst prepared by thiomolybdate intercalated NiAl LDH has the advantage of simple preparation and more hydrogenation activity center.