Catalytic mechanism of the dehydrogenation of ethylbenzene over Fe–Co/Mg(Al)O derived from hydrotalcites

Abstract

Catalytic mechanism of ethylbenzene dehydrogenation over Fe-Co/Mg(Al)O derived from hydrotalcites has been studied based on the XAFS and XPS catalyst characterization and the FTIR measurements of adsorbed species. Fe-Co/Mg(Al)O showed synergy, whereas Fe-Ni/Mg(Al)O showed no synergy, in the dehydrogenation of ethylbenzene. Ni species were stably incorporated as Ni 2+ in the regular sites in periclase and spinel structure in the Fe-Ni/Mg(Al)O. Contrarily, Co species exists as a mixture of Co 3+ /Co 2+ in the Fe-Co/Mg(Al)O and was partially isolated from the regular sites in the structures with increasing the Co content. Co addition enhanced Lewis acidity of Fe 3+ active sites by forming Fe 3+-O-Co 3+/2+ (1/1) bond, resulting in an increase in the activity. FTIR of ethylbenzene adsorbed on the Fe-Co/Mg(Al)O clearly showed formations of CO bond and π-adsorbed aromatic ring. This suggests that ethylbenzene was strongly adsorbed on the Fe 3+ acid sites via π-bonding and the dehydrogenation was initiated by α-H + abstraction from ethyl group on Mg 2+-O 2basic sites, followed by CO -Mg bond formation. The α-H + abstraction by O 2-(-Mg 2+) was likely followed by β-H abstraction, leading to the formations of styrene and H 2. Such catalytic mechanism by the Fe 3+ acid-O 2-(-Mg 2+) base couple and the Fe 3+ /Fe 2+ reduction-oxidation cycle was further assisted by Co 3+ /Co 2+ , leading to a good catalytic activity for the dehydrogenation of ethylbenzene.

Ethylbenzene dehydrogenation with CO2 over Fe-doped MgAl2O4 spinel catalysts: Synergy effect between Fe2+ and Fe3+

“…In EB dehydrogenation over iron-based oxides catalysts, Miura et al [30] considered the formation of -adsorbed intermediate on Fe 3+ acid centers, which dissociates the ␣-hydrogen reversibly as a proton on a basic site, based on H-D exchange study. A similar mechanism was also reported by Tope et al [31]: H + abstracted on Mg 2+ -O 2− basic sites, followed by further dehydrogenation to styrene via the reduction of Fe 3+ to Fe 2+ . Styrene and H 2 were simultaneously desorbed with the reoxidation of Fe 2+ to Fe 3+ .…”

Lattice Oxygen Regulation of Perovskites for Chemical Looping Oxidative Dehydrogenation of Ethylbenzene to Styrene

“…The previous studies have reported the ethylbenzene dehydrogenation mechanism. , In this case, we proposed a CL-ODH reaction pathway for ethylbenzene conversion (Scheme ). First, ethylbenzene was adsorbed to the Mn 4+ active site by hemolytic cleavage.…”

Sustainable production of styrene from catalytic recycling of polystyrene over potassium promoted Fe–Al2O3 catalyst

“…16 Iron and iron oxide (Fe 3+ ) species in the catalyst are used to stabilise the side chain double bond and aromatic ring due to Lewis acidic behaviour to prevent further chemical reaction of the depolymerised styrene molecule. 28 Additionally, iron facilitates the dehydrogenation of ethylbenzene and stabilises potassium. 29 Furthermore, considering the data observed in Table S2, † it is pretty easy to say that the involvement of radicals in the thermal process results in a more gaseous product containing methane.…”