Abstract
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 − xSrxFeyMn1 − yO3 − 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 Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ catalyst with that of an industrial potassium promoted iron (Fe–K) catalyst revealed that the Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ catalyst showed higher initial activity than the industrial Fe–K oxide catalyst. Additionally, the Ba0.4Sr0.6Fe0.6Mn0.4O3 − 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 Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ and the Fe–K catalysts in a H2O/H2 atmosphere, reduction was suppressed by the presence of H2O over the Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ catalyst while the Fe–K catalyst was reduced. In other words, Ba0.4Sr0.6Fe0.6Mn0.4O3 − 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 H2O. So the catalytic performance of Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ was superior to that of Fe–K catalyst thanks to the high redox property of the Ba0.4Sr0.6Fe0.6Mn0.4O3 − δ perovskite oxide.
Highlights
Styrene, an important monomer in petrochemistry, is used for polymeric materials such as polystyrene resin, acrylonitrile– butadiene–styrene resin and styrene–butadiene rubber
BaMnO3 − δ-BASED CATALYSTS Previous studies revealed that Mn-based and Fe/Mn-oxide catalysts showed high activity for EBDH thanks to the well-balanced rates of release and regeneration of lattice oxygen (Watanabe et al, 2009, 2011)
For EBDH, the substitution of Ba2+ for Sr2+over Ba1 − xSrxFeyMn1 − yO3 − δ (x = 0, 0.2, 0.4, 0.6, 0.8, and 1, y = 0, 0.2, 0.4, 0.6, and 0.8) catalysts enhanced the initial activity for EBDH, but activity decreased with time on stream
Summary
An important monomer in petrochemistry, is used for polymeric materials such as polystyrene resin, acrylonitrile– butadiene–styrene resin and styrene–butadiene rubber. 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). 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. The catalyst must work under low reaction temperatures and low steam conditions from the viewpoint of energy saving These severe operations might be possible thanks to high redox property of perovskite-type oxides, which could achieve a low-cost dehydrogenation process. To develop a novel La-free perovskite-type oxide catalyst, BaMnO3 − δ-based catalysts that are well known for high redox properties, were applied to EBDH with steam.
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