UV Raman spectroscopic studies of V/θ-Al2O3 catalysts in butane dehydrogenation

To explore the coke formation mechanism and catalyst structure under alkane dehydrogenation (DH) conditions, the DH of butane on V/θ-Al2O3 was explored by in situ UV Raman spectroscopy and reactivity tests. Studies of butane DH on V/θ-Al2O3 catalysts with various distributions of surface VOx species identify a structure–coke relationship. The deactivation of the catalysts in butane DH is due mainly to the formation of coke species. Both the nature and amount of coke formed are related to the structure of VOx species. Monovanadates make chain-like polyaromatics, whereas polyvanadates produce mainly sheet-like (two-dimensional) polyaromatics that are detrimental to catalytic activity. The amount of coke formed from butane DH follows this sequence: polymeric VOx > monomeric VOx > V2O5, Al2O3. Raman spectroscopy studies of butane, 1-butene, cis/trans-2-butenes, and 1,3-butadiene reactions on V/θ-Al2O3 catalysts enable the formulation of a coke formation pathway for butane DH, in which polystyrene is found to be a key intermediate. Although the surface of V/θ-Al2O3 is partially reduced under butane DH conditions, the structure of VOx species can be fully regenerated by oxidation of the coke species at temperatures up to 873 K.