Oxidative dehydrogenation of isobutane on carbon xerogel catalysts

Abstract

The oxidative dehydrogenation of isobutane was investigated with oxidized and nitrogen-doped carbon xerogel catalysts in a fixed-bed reactor at 375 ºC using a stoichiometric feed composition. The oxygen groups were selectively removed from the surface by thermal treatments performed on the oxidized samples, confirming the carbonyl-quinone groups as the active sites for the reaction, but also highlighting the negative role played by the carboxylic anhydride groups. Turnover frequencies could be calculated from correlations between the catalytic activity and the concentration of carbonyl-quinone groups. On the other hand, the results obtained with the nitrogendoped samples showed that the catalytic activity increased with the nitrogen content of the carbon xerogels.

Nanostructured mesoporous carbons: Tuning texture and surface chemistry

“…This huge variety of oxygencontaining groups can be introduced onto the carbon material surface by treatment with oxidizing agents, either in the liquid phase (e.g., nitric acid, hydrogen peroxide, ammonium persulphate) or in the gas phase (e.g., with oxygen, ozone, nitrogen oxides) [110][111][112][113][114][115][116]. For liquid phase oxidation, a diluted or concentrated solution of the oxidizing agent is boiled in the presence of the carbon material.…”

Oxidative dehydrogenation of isobutane catalyzed by an activated carbon fiber cloth exposed to supercritical fluids

“…5 and m is the catalyst mass used, 0.2 g. Scarce TOF data of metal-free carbon catalysts for this reaction have been reported. There is only one work [8], where oxidized carbon xerogels treated at different temperatures under inert atmosphere are tested, reporting an initial TOF of 3.17 × 10 −4 mol isobutene mol carbonyl-quinone −1 s −1 measured at the same conditions investigated in the present work. It must be remarked that the sample modified with HNO 3 does not appear in Fig.…”

“…This sample also contains large amounts of carboxylic acid groups, but these will be decomposed at the reaction temperature. Acidic groups tend to decrease the electron density at the active sites, thus reducing their catalytic activity [8]. The acidic character of the catalyst previously exposed to HNO 3 explains its poor ability to dehydrogenate isobutane reflected in Figs.…”

“…The oxidative dehydrogenation of isobutane is usually catalyzed by metal oxides [2][3][4][5]. However, different carbon materials, such as activated carbons (ACs) [6,7], carbon xerogels [8] or graphitic carbons [9][10][11], have emerged as alternative metal-free catalysts capable of producing isobutene.…”

“…As a result, different attempts to tailor the surface chemistry of raw carbon materials have been investigated in order to optimize the catalytic performance; doping with heteroatoms, and exposure to low-temperature oxidizing solutions (nitric acid, hydrogen peroxide) and high-temperature oxidizing (O 2 , N 2 O), reducing (H 2 ) or inert (Ar, N 2 ) gases are some of them [6][7][8][9]12].…”