(654e) Alkali-Promoted Mixed Oxide Redox Catalysts for Oxidative Dehydrogenation of Ethane in a Cyclic Redox Scheme

Chemical looping oxidative dehydrogenation (CL-ODH) of ethane utilizes a transition metal oxide based redox catalyst to convert ethane into ethylene under an autothermal, cyclic redox scheme. Unlike conventional ODH, CL-ODH eliminates the needs for gaseous oxygen, rendering a potentially safer and more efficient process.

In this presentation, we report the effects of alkali metal promoted La_0.6Sr_1.4FeO₄ (LaSrFe) as effective redox catalysts for CL-ODH. The effects of promoting LaSrFe with Li and K are investigated. Alkali metal containing promoters such as Li2O notably increased the selectivity of the pristine LaSrFe but suppressed their oxygen carrying capacity. The K-promoted LaSrFe was further characterized with Low Energy Ion Scattering (LEIS), X-ray photoelectron spectroscopy (XPS), and ¹⁸O₂-exchange experiments. LEIS analysis indicated that the surface layer contained exclusively of K₂O whereas ¹⁸O₂-exchange experiments confirmed that the oxygen surface exchange and incorporation rates are significantly lower for the K-promoted LaSrFe. Meanwhile, co-promotion of Li and K achieved up to 86% ethylene selectivity and 60% ethane conversion while maintaining a satisfactory oxygen carrying capacity. This enhanced performance was ascribed to the higher selectivity resulting from Li/K promotion, which forms an alkali metal oxide layer on the surface and inhibits the non-selective electrophilic oxygen species. Moreover, partial substitution of K on the A-site improved the oxygen carrying capacity of the redox catalyst. In addition to LaSrFe, other oxide substrates within the perovskite structure family were also investigated to determine the general effects of A-site and B-site compositions of the oxide substrate on the ODH performance of the alkali promoted redox catalysts.