A Nickel-tungsten Hydrogenation Catalyst Was Prepared Using Composite Oxide As A Carrier

Integration of high active metal dispersion and weak metal-support interaction is the most effective way to enhance the activity of transition metal HDS catalysts.The ZrO2-Al2O3 composite oxide support can weaken the W(Mo)-support interaction,but the active metal oxide tends to agglomerate into large crystallites by the impregnation(IM)method,which is hard to achieve high WO3 loading and high W dispersion.Our reasearch group had developed a microwave hydrothermal(MWH)method to achieve high WO3 loading and high W dispersion on Al2O3,which combined the rapid heating of microwave treatment and the dispersing capacity of hydrothermal conditions.The MWH method was attempted to deposit WO3 onto ZrO2-Al2O3 to prepare the HDS catalysts with high dispersion in the paper.Firstly,the ZrO2-Al2O3 support with various ZrO2 contents were synthesized by different methods and the effect of synthesis method on physicochemical properties of supports were investigated.Secondly,the WO3/ZrO2-Al2O3 catalysts were prepared by MWH method,and the reference catalysts with the same WO3 and ZrO2 contents were prepared by the conventional IM method,the influence of catalyst preparation methods and ZrO2 contents on the property and activity of catalysts were studied.Finally,the NiO-WO3/ZrO2-Al2O3 were prepared by MWH and IM methods,the influence of Ni on the property and activity of catalysts were studied.The results are given as below.1.The ZrO2-Al2O3 support were synthesized by impregnation(Imp),precipitation(Pre)and Sol-Gel(SG)methods.The support synthesized by Pre method showed higher thermostability and specific surface area and the ZrO2 was amorphous,because the crystallization was delayed by Al2O3.2.High WO3 dispersion was achieved in the WO3/ZrO2-AlO3 catalysts prepared by MWH method with 10-50 wt%ZrO2,which had not led to the formation of bulk WO3.The incorporation of ZrO2 could weaken the W(Mo)-support interaction,increase octahedrally coordinated W species and promote sulfuration of WO3,formation of shorter WS2 slabs and thus enhance the HDS activity,the catalyst with 30 wt%ZrO2 content had the highest activity.3.The bulk WO3 were formed in IM-prepared WO3/ZrO2-Al2O3 with the same WO3 and ZrO2 contents,which inreresed with increasing ZrO2 content.The poor dispersion and reducibility of bulk WO3 led to the formation of longer WS2 slabs and poor sulfidation.The IM-prepared WO3/ZrO2-Al2O3 with 10wt%ZrO2 showed slightly higher activity,the further increased ZrO2 remarkably decreases the activity.All the IM-prepared WO3/ZrO2-Al2O3 showed lower HDS activity than that of WO3/ZrO2-Al2O3 prepared by MWH method.4.MWH method could disperse more active matal on the support than IM,the actual monolayer capacity accounts for 93.1%of the theoretical threshold for MWH and 45.5%for IM.5.The introduction of Ni into WO3/ZrO2-Al2O3 is favorable to enhance the reducibility,formation of NiO-WO3 with better reducibility,improve the sulfidation of WO3 and favor forming more Ni-W-S.Compared to WO3/ZrO2-Al2O3,NiO-WO3/ZrO2-Al2O3 show extremely higher activity.