Synthesis Of Vanadium Phosphorus Oxide Catalysts Promoted By Deep Eutectic Solvents For N-butane Selective Oxidation

Selective oxidation of light alkanes(C1-C5)to valuable functionalized chemicals has been widely studied due to their economy and environmental friendliness.Up to now,the most successful example is the partial selective oxidation of n-butane to maleic anhydride(MA)by vanadium phosphorus oxide(VPO)catalysts in industry.However,there are many problems of VPO catalysts,like impurity phase,poor crystallization,poor active sites etc.,which result in the low conversion of n-butane and poor selectivity of MA.In this thesis,we intend to these problems with the purpose of improving the yield of MA,some functionalized deep eutectic solvents(DES)were designed and synthesized.The process of nucleation and growth of precursors was adjusted by DES,resulting in the higher catalytic performance of VPO.Meanwhile,the effect on physicochemical properties(crystal structure,microstructure,surface chemical state,redox characteristic and acid-base property)of DES was investigated in detail.The combination of characterizations with the performance was considered to understand the essential effects of DES.In addition,reaction parameters were optimized in the research.The main results are summarized in below:(1)The oxalic acid-base DES(ChCl/OA DES)was synthesized to solve the problem of poor crystallization and impurity phase of VPO catalysts.ChCI/OA DES can interact with V2O5 and form a new vanadium complex,which affects the process of nuclei formation of precursors by acting like a "buffer agent" in this process and obtained a single-crystal structure on the surface of precursor,correspondingly,topological transformation to the single-crystal active phase under the activation conditions accompany the decomposition of DES.What's more,ChCl/OA DES as crystal induced agent and structural modifier could induce the growth of(020)plane,reduce the average valence state of V and reduction activation energy.Catalytic performance showed that the ChCl/OA DES improved the yield of MA about 18%;(2)Based on the above work,the glucose-based DES(ChCl/GLU DES)was synthesized as structure direct agent and template agent to solve the problem of poor crystallization and poor active sites of VPO catalysts.The active crystal plane was induced by ChCl/GLU DES,which result from the-OH group can selectively adsorb to certain faces to decrease their surface energy and further the growth rate of these faces.After activation,polyporous and high crystallinity VPO catalysts were obtained with the decomposed of ChCl/GLU DES.Meanwhile,the surface acidity of VPO was reduced,which avoid the deep oxidation of MA.Catalytic performance showed that the ChCl/OA DES improved the yield of MA about 12%;(3)The reaction conditions were optimized in the tube fixed-bed reactor,mainly contain the reaction temperature and the gas hourly space velocity(GHSV).The tendency between reaction parameters and catalytic performance was summarized.