Active coke: Carbonaceous materials as catalysts for alkane dehydrogenation

Abstract

The catalytic dehydrogenation (DH) and oxidative dehydrogenation (ODH) of light alkanes are of significant industrial importance. In this work both carbonaceous material deposited on VOx/Al2O3 catalysts during reaction and unsupported carbon nanofibres (CNFs) are shown to be active for the dehydrogenation of butane in the absence of gas-phase oxygen. Their activity in these reactions is shown to be dependent upon their structure, with different reaction temperatures yielding structurally different coke deposits. Terahertz time-domain spectroscopy (THz-TDS), among other techniques, has been applied to the characterisation of these deposits -the first time this technique has been employed in coke studies. TEM and other techniques show that coke encapsulates the catalyst, preventing access to VOx sites, without a loss of activity. Studies on CNFs confirm that carbonaceous materials act as catalysts in this reaction. Carbon-based catalysts represent an important new class of potential catalysts for DH and ODH reactions.

Carbon-catalysed reductive hydrogen atom transfer reactions

“…A prolonged reaction time of 36 h was required to produce a high yield of the desired product when p-isopropylbenzyl alcohol was used as the substrate (entry 9). The C-1 catalyst also exhibits promise for direct coupling of aniline with simple electron-poor heteroaromatic alcohols under similar conditions in moderate yields (entries [10][11][13][14]. p-Methylthiobenzyl alcohol was converted to the respective secondary amine in high yield.…”

“…The catalytic reduction of cyclic ketones, such as cyclohexanone and cyclooctanone, was also achieved in 91-99% yields (entries 11-13). In addition, linear ketones with different alkyl chain lengths could be used as starting materials, and these compounds afforded the desired products in 98% yields (entries [14][15]. Therefore, our carbon catalyst system can be employed with ketone derivatives with versatile structures.…”

“…Carbon materials, including amorphous carbon, ordered mesoporous carbon, graphite/graphene (oxide) and carbon nanotubes, are widely applied in many catalytic transformations in modern organic chemistry [9][10][11] , and good performance has been obtained in the oxidation of an alkane [12][13][14][15] , alcohol [16][17][18] , amine 19 , thiol and sulphide 20,21 . These reactions encompass the oxidative hydrogen atom transfer reactions.…”

Structural changes in FeOx/γ-Al2O3 catalysts during ethylbenzene dehydrogenation

“…3 The structural changes that catalysts undergo during reaction can, however, also lead to the formation of catalytically-active phases. 4,6,7 The formation of different oxides and carbides is well known for iron catalysts, particularly in Fischer-Tropsch synthesis, 7,8 during which iron-based materials undergo complex phase changes, 9 with the identification of the active phase still disputed. 10 Carbide phases formed in situ also play a catalytic role in, e.g.…”

“…dehydrogenation and isomerisation over molybdenum oxycarbides 7 and dehydrogenation over PdC x species. 6 The dehydrogenation of ethylbenzene is a further example of a reaction where Fe based catalysts undergo structural and phase changes as a function of time on stream. Ethylbenzene dehydrogenation is the main route commercially employed in the production of styrene (Scheme 1).…”