Regulation Of Acidic Sites On CoMoS Catalyst For Hydrodeoxygenation Reaction

Using renewable energy biomass to replace fossil fuels as a transportation fuel is of great significance for environmental protection and sustainable development.However,converting lignin-derived phenols to aromatics is a long-term challenge during the hydrorefining process of biomass oil.CoMoS catalysts have a wide range of applications in the hydrodeoxygenation of phenolic compounds because of their high catalytic performance and reduced costs and hydrogen consumption.However,due to the high potential barrier of breaking the C_ar-O bond,the activity of CoMoS catalysts is usually not enough to escape the harsh reaction conditions.In order to further enhance the intrinsic activity of CoMoS catalysts,acid modification of CoMoS catalysts was carried out to improve the efficiency of C-O bond cleavage in this paper.By using the hydrodeoxygenation reaction of 4-methylphenol as a model,the regulation of acid sites on the surface for promoting the HDO reaction catalyzed by CoMoS was deeply studied.The active structure of the catalyst surface and the relationship between the active structure with the catalytic performance were also studied.The details are as follows:1.A series of Co-doped MoS_2-x catalysts were prepared by using the H₂O₂ etching method.During the etching process,the surface S vacancy of MoS₂ can be adjusted by adjusting the ratio of H₂O₂/MoS₂ to anchor the Cospecies.The optimized Co-MoS₂-2catalyst has the relatively highest HDO reaction rate,and its activity is 3.4 times higher than that of the Co-MoS₂-0 sample.Interestingly,it was also found that the catalytic activity of the Co-MoS_2-x catalyst was not closely related to the Cocontent,but was closely related to the surface acidity（Br（?）nsted and Lewis acid sites）.Based on this,we believe that the excellent activity of Co-MoS₂-2 was attributed to the surface acid sites generated during the H₂O₂ etching process.2.The role of acidic sites and their effects on activity were further studied.A simple physical mixed solid acid NbOPO₄（NbP）with Co-MoS₂in different proportions was used to assemble composite catalysts.Among them,the optimized CoMoS/NbP-4composite catalyst showed the highest activity in the hydrodeoxygenation reaction of4-methylphenol to toluene,and its reaction rate was about 3 times that of CoMoS/SiO₂（neutral）.Other Br（?）nsted solid acids,such as heteropolyacids,were further used to replace NbOPO₄ and showed similar promoting effects.It can be seen that the Br（?）nsted acid site can accelerate the activation of the C_ar-O bond when complexed with the CoMoS catalyst.Combined with the experimental results,it shows that there is a synergistic effect between the Br（?）nsted acid sites and the active phase in CoMoS,which can promote the cleavage of the C_ar-O bond and improve the catalytic activity of the hydrodeoxygenation reaction.This provides a new strategy for us to design and prepare catalysts for hydrodeoxygenation reactions in the future.