(560eg) Core-Shell Structured Mixed Metal Oxides for Oxidative Dehydrogenation of Ethylbenzene Under a Cyclic Redox Scheme
Catalytic dehydrogenation (DH) of ethylbenzene is a mature technology, accounting for 90% of the styrene produced worldwide. This technology relies on co-feeding superheated steam with ethylbenzene in the presence of a promoted, iron oxide based catalyst. The high reaction endothermicity and steam requirements lead to significant energy consumption and CO2 emissions. In addition, styrene yield is limited by thermodynamic equilibrium. To address these limitations, we propose an autothermal redox oxidative dehydrogenation (RODH) scheme, which has the potential to both reduce the energy consumption and eliminate equilibrium limitation for ethylbenzene DH reactions. In RODH, the lattice oxygen from a mixed metal oxide redox catalyst is used to convert ethylbenzene and air into separate streams of styrene and oxygen depleted air under a cyclic redox process. In the present study, we report a core-shell structured mixed metal oxide, where shell material is both catalytically active and selective in DH reaction and core material can effectively provide active lattice oxygen to combust hydrogen into steam. As such, an ethylbenzene yield significantly higher than thermal equilibrium value for regular DH reaction was obtained. The RODH reaction was determined to be highly dynamic in terms of product distributions. In-situ XRD, XPS, LEIS and TEM were performed to determine the changes in redox catalyst surface and bulk properties and to link the catalyst surface/structural changes with its catalytic properties. DFT simulation was also conducted to reveal the reaction pathway. The simulation results are supported by experimental data obtained from isotope exchange experiments using FTIR-TPSR and mass spectroscopy. Overall, the promising performance using the core-shell redox catalyst supports the potential feasibility and attractiveness of the RODH scheme.