Dehydrogenation of Ethylbenzene with Carbon Dioxide as Oxidant over Mg-modified Alumina-supported V–Sb Oxide Catalysts

Abstract

Modification of alumina support with an appropriate amount of magnesia (Mg/Al ¼ 0:1) leads to the stable activity of the supported vanadium-antimony oxide catalyst for the dehydrogenation of ethylbenzene into styrene in the presence of carbon dioxide as oxidant. Correlation between catalytic performance and surface acidity has been found.Catalytic dehydrogenation of ethylbenzene in the presence of carbon dioxide (CO 2 -EBDH) has recently been attempted to explore a new technology for producing styrene selectively because it could provide us with an energy-saving and environmentally friendly process to utilize CO 2 , a greenhouse gas, as a mild oxidant.1-3 Several families of the catalysts, mainly based on supported or mixed oxides of Fe, V, or Cr were found to be active and selective in the CO 2 -EBDH.2-14 However, most of the catalysts have usually shown strong deactivation for this reaction during even a few hours on stream. As a typical example, over Mg-Al-V mixed oxides, the initial styrene yield, 64% after 1 h on stream, decreased to 40% after 7 h. 7 The similar deactivation rate was observed also for VO x /MgO catalyst. 3 We have proposed a very active and selective catalyst, V 0:43 Sb 0:57 O x / Al 2 O 3 (VSb/Al), but its deactivation was also significant mainly owing to coke formation although the deactivation rate was less than other reported catalysts. 12,13 Since the coke precursors are easily formed through the oligomerization of olefins, facilitation of olefins desorption from a catalyst surface could minimize the carbon accumulation. Taking into consideration a basic character of electron-rich olefins including styrene, lower surface acidity of the catalyst appears to induce easier desorption of olefins from the catalyst surface. VO x catalysts loaded on MgAl oxide support exhibited a decreased adsorption and rapid desorption of propylene as compared with those on alumina.14,15 Based on these considerations, an attempt has been made to stabilize the activity of VSb/ Al catalyst in the CO 2 -EBDH by the modification of the alumina support with a basic MgO component.MgO-modified alumina (Mg n Al) supports were obtained by impregnation of an activated alumina with aqueous solutions containing a certain amount of Mg(NO 3 ) 2 . 6H 2 O (Mg n Al; n is an atomic ratio of Mg/Al ¼ 0:1, 0.3, or 0.5) followed by calcination at 670 C. Alumina (Al)-or Mg n Al-supported vanadiumantimony oxide catalysts were prepared by impregnation with the solutions of NH 4 VO 3 and SbCl 3 followed by calcination at 650 C. The loading of the supported V 0:43 Sb 0:57 O x component (20 wt %) was the same for all samples. The catalyst supports and supported catalysts were characterized by BET specific surface area (S BET ) measurements (Micrometrics model ASAP 2400), X-ray diffraction (XRD) (Rigaku D/MAX-3B diffractometer) and the NH 3 -temperature-programmed-desorption method (NH 3 -TPD) (Micrometrics, TPD/TPR 027 Option). The catalytic tests were performed with 1 g of catalyst at 595 C under atmospheric pressure in an isothermal ...

An Overview on the Dehydrogenation of Alkylbenzenes with Carbon Dioxide over Supported Vanadium–Antimony Oxide Catalysts

“…Like V-Sb/Al, the V-Sb/Mg n Al catalysts are also highly selective for styrene production, S ST > 95% [35]. As shown in Fig.…”

“…In the propane oxidative dehydrogenation, a decrease in the adsorption of propene is observed on the VO x catalysts loaded on MgO-modified alumina compared to the un-modified one [39,40]. Hence, we have chosen a basic magnesium oxide to neutralize an excessive surface acidity of the alumina support [35].…”

“…We have proposed very active and selective alumina-supported vanadium oxide catalysts in the CO 2 -EBDH [31]; their deactivation, however, is also significant although it is less than that for the reported catalysts. Therefore, the main practical aims of our recent studies [31][32][33][34][35][36][37] described and compiled in this account were to design better catalyst with more stable activity and to understand important features of the CO 2 -EBDH reaction.…”

Production of Nanostructured Vanadium Oxide Thin Films on the Surface of Metal Oxide Carriers by Thermal Decomposition of Vanadylic Organometallic Complexes (С5н5)2v=о•(тнf)5 With Cyclopentadienyl Ligands

“…Presently in industry isobutylene is produced by dehydrogenation of isobutane over chromia-alumina catalyst [4]. At the beginning of 2005 total production of isobutylene by this technology [5] made up more than 3 million tonnes. It should be noted that oxidizing dehydrogenation of isobutane attracts practitioners as a potential alternative way of producing isobutylene.…”

Effect of Mg in Alumina-Supported Sb–V–O Catalysts for the Ammoxidation of Propane into Acrylonitrile

“…Addition of an appropriate amount of magnesia (Mg/Al = 0.1) to alumina support enhances the stability of Sb-V-O catalysts for the dehydrogenation reaction of ethylbenzene into styrene [33]. This is attributed to the rapid desorption of styrene from MgAl oxide support compared to that of alumina, facilitating desorption of olefins from the catalyst surface which could minimize the carbon accumulation [34,35] and coke formation.…”