Influence of support and kind of VOx species on isobutene selectivity and coke deposition in non-oxidative dehydrogenation of isobutane

• VOx on SiO2, Al2O3, and SiO2-Al2O3 were tested in dehydrogenation of isobutane.
• VOx on Al2O3 showed much higher selectivity than VOx on SiO2 or SiO2–Al2O3.
• Selectivity is determined by activity for isobutene isomerization to n-butenes.
• Isomerization is catalyzed by acidic sites of support and by VOx bound to silica.
• Coke can be formed via isobutene or via n-butene–butadiene.

Non-oxidative dehydrogenation of isobutane was investigated over VOx/MCM-41, VOx/Al2O3 and VOx/SiO2–Al2O3 (1–70 wt.% SiO2). The highest selectivity to isobutene of around 85% at isobutane conversion of 50% was achieved over VOx/Al2O3, while all other catalysts were significantly less selective and performed similarly to each other. The lower selectivity obtained on VOx/MCM-41 and VOx/SiO2–Al2O3 is related to their higher activity for isomerization of isobutene to n-butenes as concluded from the results of separate tests with these olefins used as feed components. Our characterization studies suggest that the above isomerization reaction is catalyzed by both, Lewis acidic sites of support and VOx species. Skeletal isomerization activity of the latter depends on their polymerization degree and indirectly affects coke formation because, in addition to isobutene, butadiene formed from n-butenes opens an additional pathway to carbon deposits.

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