Study In Dehydrogenation Reaction Of Isobutane Over Cr Catalysts By Microwave Method

Based on the Russia's latest research on isobutane dehydrogenation fluid catalysts with preliminary studies,the aim of this paper was to introduce the microwave technology into the catalyst preparation.The effects of microwave on catalytic activity of the isobutane dehydrogenation and structural performance.As Cr-K/?-Al₂O₃ catalysts,the catalytic performance of the catalysts obtained by microwave was better than by conventional method.The results of XRD,BET,27 Al MAS NMR,and Raman indicated that the microwave method could dec rease the particle size of catalysts more evenly,and improve the degree of dispersion of active constituent on the supporter in contrast to the catalyst prepared by conventional method.Furthermore,part of metal Cr3+ species occupies sites on/in A12O3 in close vicinity of tetrahedral 27 Al,forming the stable structure-[AlO4]-Cr.And the isolated Cr6+,mono and polychromatic species,which seemed to play a key role in the isobutane dehydrogenation,were identified using Raman spectroscopy.The results sho wed that the catalyst prepared by microwave method possessed a higher number of Cr6+ species compared to the catalyst prepared by conventional method.The optimum microwave operation parameters were studied.Experimental results showed that microwave method could improve isobutane dehydrogenation activity of catalyst greatly?the isobutylene yield is from 45.8% to 54.2%?.The optimum microwave parameters were that microwave dipping condition was 175 W,3min,and microwave drying condition was 600 W,2min.The characterization results showed that the appropriate microwave conditions could improve the pore structure and degree of dispersion of active constituent,the particle size became smaller and distributed more uniformly.The effects of microwave method on Cr loadings,the content of additive K,calcinationConditions and the amount of catalyst were studied.The results showed that compared with the industrial catalyst FBD-4?12.5 wt%?,the Cr loading?7.5 wt%?of catalyst prepared by microwave method,decrease 5.0%;O n Condition that the content of additive K was 2.0 wt%,and calcination temperature was 550?,and the amount of catalyst was 3mL,the isobutane conversion and isobutylene yield exhibited the highest,respectively,69.2%,57.2%;The regeneration capability of Cr-K/Al₂O₃ catalysts prepared by microwave method was discussed as well,thus the results were: the Cr-K/Al₂O₃ catalysts had long one-way life and its isobutene yield was still maintained at 43.2% after the catalyst regenerated again.It was also found that regenerated catalyst exhibited almost the same activity and selectivity as the corresponding fresh material.