Applicability of protolytic mechanism to steady-state heterogeneous dehydrogenation of ethane revisited

This article revisits the applicability of the traditional protolytic mechanism in heterogeneous activation of ethane on the basis of new evidences achieved through various molecular sieves, and gives an overview of the progress in catalytic dehydrogenation of ethane to ethylene in the presence or absence of an oxidant. The results of acidic and alkali metal ion catalysts have been compared to those on chromium and iron oxides. The mechanism of activation over acidic sites has been explored by preventing the interference of oxidant. All of the acidic catalysts played a negative role in ethane dehydrogenation. Even oxygen as a strong reactive agent could not alter the prevailing mechanism. The new experimental data proved that a Brønsted acid–Lewis base mechanism of activation is not effective in this event. A Lewis acid–hydride ion mechanism was alternatively realized as the favored pathway from ethane to ethylene. The effect of the presence of alumina sites in a silica framework in activation of ethane is also dissected.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The structures investigated were LTA, MFI, Y, SAPO, and MCM. ► Acidic sites and alkali metal ions were not effective in activation of ethane. ► Ethane activation prerequisites are different from those of higher alkanes. ► A Lewis acid–hydride ion mechanism is the favored pathway from ethane to ethylene. ► The electron configuration and reducibility of the catalyst are very important.