| Lignin mainly exists in the complex phenolic compounds of the woody parts of plants,and is the only renewable resource in nature that can directly provide aromatic rings.molybdenum based supported catalysts have been extensively studied by researchers due to their excellent fracture selectivity for C-O bonds in lignin structures and unique hydrodeoxidation ability for lignin depolymerized intermediates.however,due to improper carrier selection,the molybdenum-based catalyst produced a large amount of carburizing and sintering during the reaction,which greatly reduced the catalytic activity of the molybdenum-based catalyst.The selection and design of catalysts is an important factor to promote the solution of lignin in supercritical system.This study selected molybdenum(Mo)as the active component of the supported catalyst.using natural mineral sepiolite as the supported system to prepare molybdenum/sepiolite(Mo/SEP)catalyst,the effect of molybdenum-based sepiolite catalyst on lignin catalytic depolymerization was investigated in supercritical ethanol medium.by exploring the temperature,time,Mo metal loading and doping modification of nonmetallic elements,the optimal performance heterogeneous molybdenum-based catalyst and the optimal catalytic depolymerization lignin process conditions were obtained.Mo/SEP catalysts(10%molybdenum content)were prepared by wet impregnation using acidified modified sepiolite as heterogeneous catalyst support.The results showed that the optimum conditions for catalytic depolymerization of lignin.were temperature 290? and 4 h,At this time,the liquefaction rate of lignin was 63.5%,and the yield of soluble products of petroleum ether reached 47.6%.XRD?FTIR results show that mo species in the mo/sep exist in the form of MoO3,and the surface species undergo obvious crystalline phase transition during depolymerization.xps results show that the reaction temperature has a significant effect on Mo5+ active components.when the reaction temperature reaches the optimum temperature(290?),the Mo5+ species content reaches the maximum.at this point,lignin-catalyzed depolymerization Mo/SEP the transformation path from Mo6+ to Mo5+ in the catalyst is the main transformation process.Mo/SEP catalysts with different mo contents(5%,10%,20%,40%,60%)were prepared by wet impregnation to explore the effect of loading on the surface structure,active sites and acid site content of the catalysts.The surface structure and active sites of the catalyst were analyzed by XRD?FTIR?XPS,and the changes of acidic sites on the surface of the catalyst were analyzed by infrared adsorption of NH3-TPD?Pyridine.XRD?XPS results show that the catalyst surface species gradually change from the Mo4O11?Mo9O26 of transition state to the ?-MoO3 of stable state with the increase of loading amount,and the formation of Mo4O11?Mo9O26 two unsaturated transition states is caused by the interaction of mo species and elements on the support surface.ftir results show that the catalyst contains three types of Mo-O bonds(Mo=o?Mo-O-Mo?3Mo-O),and the amount of terminal oxygen(Mo=O?Mo-O-Mo?3Mo-O)and intralayer bridging oxygen(Mo-O-Mo(2))on the catalyst surface increases with the increase of the amount of mo loading.furthermore,compared to pure moo3,mo/sep catalysts,there is a higher content of terminal oxygen and intra-layer bridging oxygen.By contrast experiment,it was found that 40%Mo/SEP catalyst had the highest reactivity,among which the liquefaction rate reached 97.6%and the soluble yield of petroleum ether reached 75.1%.Finally,the catalyst was separated and collected after the reaction,and the characterization methods such as XRD?FTIR and XPS were used to characterize the catalyst after the reaction.the surface active sites,oxygen defects and other factors of the catalyst after the reaction were explored,and the structure and stability changes of the catalyst during the catalytic process were studied.in addition,the catalyst was reduced by calcination in a calciner to explore the regeneration of the catalyst. |
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