Lanthanoid-free perovskite oxide catalyst for dehydrogenation of ethylbenzene working with redox mechanism

ORIGINAL RESEARCH ARTICLE published: 23 October 2013 doi: 10.3389/fchem.2013.00021 Lanthanoid-free perovskite oxide catalyst for dehydrogenation of ethylbenzene working with redox mechanism Ryo Watanabe 1 , Maiko Ikushima 2 , Kei Mukawa 2 , Fumitaka Sumomozawa 2 , Shuhei Ogo 2 and Yasushi Sekine 2* 1 2 Department of Materials Science and Chemical Engineering, Faculty of Engineering, Shizuoka University, Hamamatsu, Japan Department of Applied Chemistry, School of Science and Engineering, Waseda University, Tokyo, Japan Edited by: Viswanathan Balasubramanian, Indian Institute of Technology, Madras, India Reviewed by: Andrzej Kolodziej, Institute of Chemical Engineering of the Polish Academy of Sciences, Poland Zheng Ren, University of Connecticut, USA Krishnamurthy K. Ramaswamy, Indian Institute of Technology, Madras, India *Correspondence: Yasushi Sekine, Department of Applied Chemistry, School of Science and Engineering, Waseda University, 65-301A, 3-4-1, Okubo, Shinjuku, Tokyo 1698555, Japan e-mail: For the development of highly active and robust catalysts for dehydrogenation of ethylbenzene (EBDH) to produce styrene; an important monomer for polystyrene production, perovskite-type oxides were applied to the reaction. Controlling the mobility of lattice oxygen by changing the structure of Ba1 − x Srx Fey Mn1 − y O3 − δ (0 ≤ x ≤ 1, 0.2 ≤ y ≤ 0.8), perovskite catalyst showed higher activity and stability on EBDH. The optimized Ba/Sr and Fe/Mn molar ratios were 0.4/0.6 and 0.6/0.4, respectively. Comparison of the dehydrogenation activity of Ba0.4 Sr0.6 Fe0.6 Mn0.4 O3 − δ catalyst with that of an industrial potassium promoted iron (Fe–K) catalyst revealed that the Ba0.4 Sr0.6 Fe0.6 Mn0.4 O3 − δ catalyst showed higher initial activity than the industrial Fe–K oxide catalyst. Additionally, the Ba0.4 Sr0.6 Fe0.6 Mn0.4 O3 − δ catalyst showed high activity and stability under severe conditions, even at temperatures as low as 783 K, or at the low steam/EB ratio of 2, while, the Fe–K catalyst showed low activity in such conditions. Comparing reduction profiles of the Ba0.4 Sr0.6 Fe0.6 Mn0.4 O3 − δ and the Fe–K catalysts in a H2 O/H2 atmosphere, reduction was suppressed by the presence of H2 O over the Ba0.4 Sr0.6 Fe0.6 Mn0.4 O3 − δ catalyst while the Fe–K catalyst was reduced. In other words, Ba0.4 Sr0.6 Fe0.6 Mn0.4 O3 − δ catalyst had higher potential for activating the steam than the Fe–K catalyst. The lattice oxygen in perovskite-structure was consumed by H2 , subsequently the consumed lattice oxygen was regenerated by H2 O. So the catalytic performance of Ba0.4 Sr0.6 Fe0.6 Mn0.4 O3 − δ was superior to that of Fe–K catalyst thanks to the high redox property of the Ba0.4 Sr0.6 Fe0.6 Mn0.4 O3 − δ perovskite oxide. Keywords: dehydrogenation of ethylbenzene, perovskite oxide catalyst, redox mechanism, stable under severe conditions, styrene production, lattice oxygen INTRODUCTION Styrene, an important monomer in petrochemistry, is used for polymeric materials such as polystyrene resin, acrylonitrile– butadiene–styrene resin and styrene–butadiene rubber. The production volume of styrene is 30 million tons per year worldwide (Meima and Menon, 2001; Su et al., 2005; Won and Jang, 2011). Styrene is produced via catalytic dehydrogenation of ethylbenzene (EBDH) according to the following chemical equation (Equation 1) (Cavani and Trifirò, 1995). C8 H10 → C8 H8 + H2 (1) As an endothermic reaction, EBDH requires high temperatures for high conversion of ethylbenzene because of thermodynamic limitations. An iron-based catalyst promoted by potassium and many kinds: Cr2 O3 , MoO3 , CeO2 , and Pd is used as an industrial catalyst (Kearby, 1945; Eggertsen and Voge, 1947; Pitzer, 1958; Lee, 1974; O’Hara, 1975; Riesser, 1979; Hirano, 1986; Rokicki et al., 2004). In the industrial process, steam is supplied with EB for increasing the equilibrium conversion by decreasing the www.frontiersin.org partial pressure of EB. Additionally, steam has roles of heating up the reactant fluid, supplying heat for the endothermic reaction, and inhibiting coke deposition on the catalyst. A disadvantage of EBDH with steam is a large amount of energy loss because of the supply of superheated steam. Therefore, development of a catalyst that can work under low steam conditions and at low temperatures has been pursued. For energy resource conservation, oxidative dehydrogenation of ethylbenzene (ODH) has recently been emphasized and investigated widely. Because ODH is an exothermic reaction, high conversion can be achieved at lower temperatures than from nonoxidative dehydrogenation. Meso-structured CeO2 (Xu et al., 2009), V2 O5 /CeO2 /Al2 O3 (Reddy et al., 2007), and Mg(VO4 )2 MgO (Chang et al., 1995) catalysts were reported as highly active catalysts working at low temperatures of around 723 K for ODH. Onion-like carbon (Su et al., 2005, 2007, 2010) and carbon fibers (Zhao et al., 2007) have also been reported as catalysts showing high activity for ODH. However, because of the combustion of EB and styrene, ODH processes presented some problems such as the decrease of selectivity to styrene. Therefore, the selectivity October 2013 | Volume 1 | Article 21 | 1 Watanabe et al. EBDH dehydrogenation over perovskite catalyst to styrene was low in the ODH process: about 68% at the EB conversion rate of 91% (Keller et al., 2002). An application of N2 O and CO2 to ethylbenzene dehydrogenation has been conducted to attain high selectivity to styrene, N2 O, and CO2 were used instead of O2 to avoid the combustion of styrene and EB, to CO and CO2 (Sugino et al., 1995; Sakurai et al., 2000a, 2002; Shiju et al., 2005). As for using N2 O as the oxidant for ODH of ethylbenzene, high styrene yield was obtained at low temperature, however the selectivity to styrene was low due to the production of styrene oxide as well as benzene and toluene (Shiju et al., 2005). Vislovskiy et al. (2002) and Park et al. (2003) investigated EBDH in the presence of CO2 over V–Sb/Al-oxide catalyst. They stated that a redox-type mechanism proceeded on V–Sb/Al-oxide catalyst, which achieved high activity and selectivity to styrene. CO2 was considered to be a desirable oxidant for EBDH. Although high activity and stability was acquired over activated carbon-supported vanadium catalyst which was promising dehydrogenation catalyst, deactivation proceeded on the catalyst due to coke deposition. Sakurai et al. investigated the catalytic properties of V/AC catalyst for EBDH with CO2 (Sakurai et al., 2000b). The catalyst revealed high activity and selectivity to styrene, but deactivation was not prevented. From these backgrounds, development of a novel dehydrogenation catalyst which has high stability as well as high activity is considered to be required. We previously investigated the reaction mechanism of EBDH with steam over the industrial potassium promoted the iron catalyst (Fe–K) catalyst, and found for the first time that oxidative dehydrogen (...truncated)