Non-oxidative Dehydrogenation Of Isobutane Research Articles

Non-oxidative dehydrogenation of isobutane over supported vanadium oxide: nature of the active sites and coke formation

We combine Raman spectroscopy, EPR, XPS, temperature programmed reduction, XRD, 51V MAS ssNMR, TEM and N2-physisorption to unravel structure–activity relationships during the non-oxidative dehydrogenation of isobutane over a V based catalyst.

Study of coke deposited on a VOx-K2O/γ-Al2O3 catalyst in the non-oxidative dehydrogenation of isobutane

Coke deposition is commonly identified as the main cause of deactivation for dehydrogenation (DH) catalysts. The VOx-K2O/γ-Al2O3 catalysts for non-oxidative DH of isobutane were studied to better understand the formation and nature of coke. Coke deposition influenced VOx species and acid sites, leading to a deterioration of DH performances. The coke was identified as aliphatic and polyaromatic species. As the DH reaction proceeding, the deposited carbonaceous species progressively transformed from aliphatic into aromatic species, with aromaticity increasing. They continuously shift between metallic VOx species and acid sites. Of note is that the aromatic species eventually condense onto the support resulting in polyaromatic and graphitic carbon mixtures. A possible coke generation process was proposed, which contained consecutive reactions such as cracking, oligomerization, and aromatization. The establishment of the coke formation mechanisms and study of the nature of the deposited coke provide guidance for future DH catalyst optimization while reducing coke formation.

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

Non-oxidative dehydrogenation of isobutane was investigated over VOx/MCM-41, VOx/Al2O3 and VOx/SiO2–Al2O3 (1–70wt.% 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.

Selective and stable iso-butene production over highly dispersed VOx species on SiO2 supports via combining oxidative and non-oxidative iso-butane dehydrogenation

For the first time, we demonstrated that combining oxidative and non-oxidative dehydrogenation of iso-butane in one reactor system is an attractive approach for iso-butene and hydrogen production. Iso-butene yields above 40% at iso-butene selectivity above 80% and CO(x) selectivity below 2% were achieved over SiO(2)-supported highly-dispersed VO(x) species during at least 20 h on-stream at 833 K.

Bimetallic PtSn/C catalysts promoted by ceria: Application in the nonoxidative dehydrogenation of isobutane

A series of bimetallic platinum–tin catalysts supported on CeO 2/C were prepared and tested in the nonoxidative catalytic dehydrogenation of isobutane. Pt–Sn/CeO 2/C catalysts with varying Sn content (Sn/Pt = 0, 0.25, 0.5, and 0.75) were prepared using a co-impregnation method and chlorinated metal precursors. They were characterized by XPS and by CO and ethylene adsorption microcalorimetry at room temperature after in situ reduction treatments. It was found that the presence of cerium in bimetallic catalysts inhibited reduction of tin species, whereas tin facilitated reduction of cerium(IV) to cerium(III). Reduction at 773 K caused a strong decrease in CO saturation coverage for all catalysts studied. For the bimetallic catalysts, a strong interaction between tin and platinum produced significant changes in the initial heat of CO adsorption. The presence of cerium caused a strong decrease in the heat of ethylene adsorption on platinum in catalysts reduced at high temperature. The monometallic Pt catalyst undergoes a fast deactivation with time on stream in the isobutane dehydrogenation reaction. The addition of tin strongly suppresses the deactivation process. It was found that cerium-containing catalysts showed higher isobutene yields compared with their corresponding cerium-free counterparts. The bimetallic catalyst with Sn/Pt = 0.5 showed the best isobutene yield, and it was studied further. This optimized catalyst demonstrated good deactivation behaviour (comparable with the best catalysts reported in the literature). Furthermore, oxidation treatment at a mild temperature (573 K) allowed recovery of nearly all of its catalytic properties.