Investigationon Preparation And Properties Of CoMo/TiO₂-Al₂O₃ Hydrodesulfurization Catalyst

Since January 1,2019,Chinese Government promulgated the National ? Fuel Standard,which indicated that the quality of fuel should be comprehensively improved forreducing the pollutant emissions.Hydrodesulfurization?HDS?is widely used in the world as the mainstream oil refining process,and the preparation of catalyst is its core technology.The main purpose of this paper is to develop the HDS catalyst for FCC gasoline.This kind of catalyst is more efficient,environmentally friendly and cost-cutting than the traditional industrial catalysts.In this paper,based on the characterization results from the low temperature N₂adsorption-desorption,XRD,SEM,H₂-TPR,etc.,the effects of different preparation methods on the desulfurization performance of the catalyst were investigated by using Co-Mo as active component,TiO₂-Al₂O₃ as composite carrier and thiophene as model compound.Furthermore,the parameters of pre-sulfurization process and HDS process were optimized in a pressurized fixed bed reactor.The results indicated that the catalyst prepared by one-pot method possessed the best HDS performance.In addition,the decomposition and dispersion of precursors of active components and the decomposition of pseudo-boehmite occurred simultaneously during calcination,which had a certain effect on the formation of structural phases.Not only did it improve the pore structure property and make the active component disperse well,but also it improved the vulcanization degree and generated more active centers.It was found that the catalyst was most thoroughly vulcanized after 1.5h of pre-vulcanization by mixed vulcanization at 300?and 3.5MPa.Under the conditions of reaction temperature280?,reaction pressure 3.5MPa,liquid space-time velocity 2h^-1 and volume ratio of hydrogen to oil 700,the catalytic efficiency could be maximized,the energy consumption could be saved and the cost could be reduced within the effective range.Secondly,the effects of different complexing agents on the catalytic performance of one-pot catalysts were investigated.Taking citric acid?CA?as an example,the effects of CA introduction mode and addition amount on its catalytic performance were explored.The experimental results indicated that the addition of complexing agent could improve the interaction between metal and carrier to a certain extent,improve the dispersion of active components,promote the sulfur reduction of catalyst,so the activity was improved.However,different complexing agents had different effects on their activity.The catalyst prepared by impregnating CA with post-treatment method had the strongest removal ability of thiophene,and the optimum addition was CA/Co=1.5.CA modification could delay the sulfuration of Co,inhibit the formation of tetrahedral Mo species and promote the formation of octahedral Mo species,thus facilitating the stacking of MoS₂ sheets and the formation of more Co-Mo-S???active phases.In order to further improve the HDS efficiency of one-pot catalysts,the related metal additives were modified,and the effects of different metal additives on the desulfurization performance were explored.Taking Ce as an example,the effect of adding order and amount of Ce on desulfurization activity were investigated in detail.The results indicated that Ce modified catalyst had higher activity than Fe and K.The removal efficiency of thiophene could reach more than 98%by adding Ce and then CoMo in the order of adding metal,containing 1.5%Ce.Ce could modify the carrier to form more pore structure,which was conducive to the attachment of active metals and the exchange of substances in the reaction.Besides it could weaken the interaction between active metals and composite carriers to a certain extent,and promote the sulfur reduction of CoMo active metals.