The advantage of ceria loading over V2O5/Al2O3 catalyst for vapor phase oxidative dehydrogenation of ethylbenzene to styrene using CO2 as a soft oxidant

Abstract

The present work highlights the influence of ceria over vanadia/alumina for the oxidative dehydrogenation of ethylbenzene to styrene with CO 2 as a soft oxidant. Various weight loadings (0, 3, 5, and 7 %) of ceria were incorporated into 10wt % V 2 O 5 /Al 2 O 3 catalyst by wet impregnation process. Structural and textural characterizations of the catalysts were performed by means of powder X-ray diffraction, temperature-programmed reduction, temperature-programmed desorption of CO 2 , N 2 adsorption-desorption analysis. Over 10 % V 2 O 5 /Al 2 O 3 , ethylbenzene conversion decreases from 62 to 49 % in a spam of 12 h. Ceria-incorporated catalyst (3 % CeO 2 /10 % V 2 O 5 /Al 2 O 3 ) showed steady ethylbenzene conversion of nearly 65 % with a styrene selectivity of 96 % for a period of 12 h time. Improved catalytic activity observed on this catalyst can be attributed to the increase in the number of redox/active VO x species after incorporation of ceria. The redox properties of 3 % CeO 2 /10 % V 2 O 5 /Al 2 O 3 and 10wt % V 2 O 5 /Al 2 O 3 were examined by reaction of CO 2 in pulses on to the partially reduced catalysts. The spent catalysts were characterized using XRD & TPR analysis to assess the reason for the deactivation of catalysts.

Comparison of single-bed oxidative dehydrogenation of ethylbenzene with double-bed using CO2

“…Styrene (ST) is one of the platform chemicals for plastic and petrochemical industries, utilized primarily for the synthesis of polystyrene and ST copolymers such as acrylonitrile-butadiene-styrene (ABS), styrene acrylonitrile (SAN), styrene-butadiene rubber (SBR), fibers, ABA resin etc. [1][2][3][4][5][6]. At present, there are two main processes for the manufacture of ST.…”

“…In the first one, ST is produced as a sideproduct in the epoxidation of propene with ethylbenzene (EB) hydroperoxide with Mo complex based catalysts. The second one and also the most important manufacturing route to ST is by the direct dehydrogenation of EB on iron oxide catalysts at 873-973 K, just below the decomposition temperature of the reactant [2,[6][7][8][9]. Because the reaction is highly endothermic and volume-increasing, a large amount of superheated steam is used to supply heat, decline the partial pressure of the reactants to shift the equilibrium to ST, and inhibit the buildup of coke or of coke precursors on catalyst surface to prolong the catalyst activity, and eventually keep the iron oxide in an appropriate oxidation state [8,[10][11][12].…”

“…Because the reaction is highly endothermic and volume-increasing, a large amount of superheated steam is used to supply heat, decline the partial pressure of the reactants to shift the equilibrium to ST, and inhibit the buildup of coke or of coke precursors on catalyst surface to prolong the catalyst activity, and eventually keep the iron oxide in an appropriate oxidation state [8,[10][11][12]. However, the use of steam has a number of defects including waste of a large amount of latent heat of condensation during subsequent separation in the conventional process instead of being recovered, catalyst deactivation, and depletion of EB and ST by steam reforming [2,8,9,[13][14][15].…”

“…To overcome the mentioned flaws in the commercial process with steam many efforts have been put forward to improve the process by making it steam-free and applying lower temperatures. Therefore, other oxidants have been examined in oxidative dehydrogenation (ODH) of EB including dry air, O 2 , CO 2 , N 2 O, and SO 2 [2,5,6,16]. Dehydrogenation in the presence of O 2 , however, requires less energy, it leads to burning a significant amount of valuable hydrocarbon [5,17].…”

“…As a consequence, ODH of ethylbenzene with CO 2 as a soft oxidant has attracted a considerable attention [5,13,17,19,[21][22][23][24]. ODH of EB (3) in the presence of CO 2 proceeds via two reactions [1,2]: first EB is dehydrogenated to ST and H 2 (Eq. 1), subsequently CO 2 employed in this reaction reacts with H 2 produced in the EB dehydrogenation reaction to yield CO and H 2 O via RWGS (Eq.…”