Research On The Synergistic Effect Of Bimetallic Catalysts In Co-Hydrogenation Processing Of Coal And Oil

As a new type of composite catalyst,the bimetallic catalyst has been confirmed to have a synergistic effect in the co-hydrogenation processing of coal and oil.but its synergistic mechanism is not clear.To further improve the conversion depth and product quality of the coal/heavy oil co-hydrogenation reaction,it is necessary to conduct more in-depth research on the synergistic effect between the metals of the bimetallic catalyst.In this study,the catalytic hydrogenation activity of a variety of single metal and bimetal composite catalysts was first investigated in the coal/heavy oil hydrogenation co-refining reaction system,Furthermore,the universality of the carrier coal modification method for different coal types has been studied.The CHSN elemental analysis,FTIR,¹³C-NMR,SEM,and other analytical methods are used to study the effect of catalyst modification on the composition and structure of the reaction products;Additionally,density functional theory（DFT）calculations were conducted to study the key roles of Fe-Ni catalyst in the reaction process,and to probe the catalytic mechanisms of the adsorption and dissociation process of hydrogen molecules;finally,the catalytic turnover frequency（TOF）of the reaction catalyst and the adsorption strength of active hydrogen is correlated to further clarifies the synergistic effect of the bimetallic catalyst.Research shows that compared with the monometallic Fe and monometallic Ni catalysts of the same amount,the bimetallic Fe-Ni composite catalyst has an obvious synergistic effect in the co-hydrogenation processing of coal and oil.A carbonaceous solid conversion efficiency above 95%was reached and the oil yield exceeded 71.5 wt%with the equimolar ratio of Fe-Ni composite catalyst（Fe₁-Ni₁）.and the ratio of coke formation is greatly reduced after the co-hydrogenation processing reaction.The calculation results of DFT show that the initial adsorption states of hydrogen molecules on the surface of Fe S（001）、Ni₃S₂（110）and Fe_4.5Ni_4.5S₈（111）catalysts are all For physical adsorption,the adsorption structure does not affect the activation of hydrogen.The smaller the dissociation activation energy of hydrogen molecules,the easier the dissociation reaction is,which indirectly reflects the catalytic hydrogenation activity of the catalyst.The study on the dissociation process of hydrogen molecules found that compared to the dissociation of hydrogen molecules on the surface of Fe S（001）and Ni₃S₂（110）,the hydrogen molecules on the surface of Fe₁-Ni₁ bimetallic composite catalyst Fe_4.5Ni_4.5S₈（111）is easier to dissociate,and the corresponding active hydrogen would be generated only by crossing the reaction energy barrier of 0.37 e V.Therefore,the bimetallic Fe-Ni composite catalyst exhibits strong intrinsic activity.Due to the lattice strain effect and the ligand effect,the adsorption strength of the catalyst for active hydrogen shows a significant difference.When the ratio of Fe:Ni in the bimetallic iron-nickel composite catalyst is 1:1,the adsorption energy of active hydrogen on the Fe_4.5Ni_4.5S₈（111）surface is-0.63e V,which corresponds to the maximum TOF in the catalytic volcano curve.Compared with the coal/heavy oil hydrogenation co-refining reaction under the monometallic iron and monometallic nickel catalyst system,the reaction system corresponding to the Fe₁-Ni₁ bimetallic catalyst has a higher catalytic hydrogenation reaction rate,which is manifested as a catalytic synergistic effect between the bimetallic Fe-Ni.