(212c) Effect of Lanthanum Doping and Chlorine Addition on Strontium Titanate Perovskites for Electrocatalytically-Assisted Oxidative Dehydrogenation of Ethane

Oxidative dehydrogenation (ODH) of alkanes is an important catalytic reaction that is widely studied. It can be used to convert less valuable alkanes, such as ethane, to more valuable olefins, such as ethylene. However, the further oxidation of olefins to carbon dioxide and carbon monoxide limits the selectivity of the process [1]. Oxide ion-conducting electrolyte reactors allow for controlling oxygen availability to the reaction and thus, improve the selectivity for olefin formation [2, 3]. The reactor setup is similar to solid oxide fuel cells with an important difference: instead of generating power as in solid oxide fuel cells, an external current is applied to control the oxygen flux through the electrolyte. When the current is applied, the oxygen molecules at the cathode side are ionized to O^-2 ions. Oxygen ions conduct through the oxygen ion-conducting electrolyte to the anode, where they react with ethane to form ethylene. Since the amount of oxygen conducted through the electrolyte can be controlled by the current applied, this can help regulate the alkane conversion and selectivity.

In this study, strontium titanate type of perovskites were tested as anode catalysts for electro ODH reaction. La-doped strontium titanates were synthesized via modified Pechini route. The effect of lanthanum doping and chlorine incorporation on these catalysts was investigated. The characteristics of the catalysts were investigated using N₂ physisorption, ambient and in-situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared spectroscopy (DRIFTS), and electronic conductivity measurements. Besides Electro-ODH experiments to test the activities, impedance measurements were also taken using to better understand the cell characteristics and resistances. Oxygen flux measurements were also performed.

Electro-ODH tests on the cell with La_0.2Sr_0.8TiO_3±δCl_Ï? anode showed that ethane conversion and ethylene production rates increase with increasing current. Hydrogen production rates were also observed to be very low, indicating oxidative dehydrogenation is taking place. It was also observed that Cl addition increases the ethylene selectivity and La doping increases the conductivity of strontium titanate.

1. Kung, H.H., and Kung, M.C., Applied Catalysis A: General 157, 105 (1997).

2. Coronas, J., Menendez, M., and Santamaria, J. Industrial & Engineering Chemistry Research 34, 4229 (1995).

3. Sundmacher K., Rihko-Struckmann, L.K., Galvita, V., Catalysis Today 104, 185 (2005).