Study Of The Structure And Catalytic Effect Of Mg-modified VO_x/Al₂O₃ Catalysts For Propane Dehydrogenation

Vanadium based catalysts are promising materials for the development of the dehydrogenation of propane.Among the metal oxides that have been investigated for the dehydrogenation of propane,except CrO_x based catalysts which is already used in the industry,vanadium based catalysts have shown a higher activity and better stability even after many regeneration steps.In addition,their relatively low cost comparing to Pt and their friendly environmental character made them more commercially attractive.However,as all the catalysts developed for dehydrogenation processes,vanadium catalysts suffer from a quick deactivation which is essentially due to the coke deposition on the catalyst surface.In order to suppress this phenomenon,we have studied the promotion effect of magnesium oxide over vanadium catalyst supported on alumina.A series of VO_x/Al₂O₃ and Mg-modified VO_x/Al₂O₃ catalysts were synthesized by an incipient wetness impregnation method and the catalysts were carefully characterized by Raman spectra,UV-Vis spectra,STEM,TGA and in situ DRIFTS.We have showed that the stability of a 12V/Al₂O₃ catalyst was significantly improved upon addition of small amounts of MgO.Experimental evidences indicate that V₂O₅ nanoparticles emerge in the 12V/Al₂O₃ samples,and appropriate Mg addition helps dispersing the V₂O₅ nanoparticles into 2D VO_x species which leads to an increase of the activity.In the same time,a decreasing in the coke formation on the catalyst surface and an improving stability of the catalyst in non-oxidative dehydrogenation of propane was observed.To provide a full understanding of this work,we have set the scene by the description of propylene production and by detailed discussions about the dehydrogenation of propane in the first chapter of this thesis.In the second chapter,some of the previous investigations on supported vanadium catalysts were presented to provide an understanding on its behavior with various supports,its active sites and its deactivation process.The third and the fourth chapter were respectively about the experimental and the results/discussions of the promotion of VO_x/Al₂O₃ with MgO.