Enhanced role of graphitic-N on nitrogen-doped porous carbon ball for direct dehydrogenation of ethylbenzene

Abstract

Nitrogen doping is an efficient strategy to improve the catalytic activity of carbocatalysts in direct dehydrogenation reactions. The interpretation of enhanced activity is now mainly attributed to the strengthened basicity. On the other side of doping, electronic properties that differed in various nitrogen doping configurations, however, were barely considered. Herein, to elucidate the role of graphitic N, pyridinic N and pyrrolic N, N-doped porous carbon balls with tunable contents of these nitrogen species were used as moulded carbocatalysts for steam-free direct dehydrogenation of ethylbenzene to styrene. Along with CO groups that were commonly certified as active sites on carbocatalysts, graphitic N contributes to the styrene yield. The former serves as active site that directly activates and dissociates C–H bond, while the latter one provides additional electrons into the delocalized π-system and leads to improved chemical reactivity of CO. The loss of CO active sites is not only attributed to the carbon deposition as illustrated by the elevated area ratio of D3 to G band in Raman spectra, but also its failed regeneration from intermediate hydroxyl groups (C–OH), which was proved by the tiny thermal decomposed products of CO and H2O as detected by the on-line mass spectrometry and gas chromatography.