(40d) Thermo-Catalytic Versus Electro-Catalytic Hydrocarbon Activation: Enhancing Olefin Selectivity By Controlling the Oxide Ion Transfer

Oxidative dehydrogenation (ODH) of alkanes and oxidative coupling of methane (OCM) are scientifically and industrially important hydrocarbon activation reactions that occur in the presence of oxygen. The addition of oxygen to the reaction medium turns endothermic dehydrogenation and coupling reactions to an exothermic reaction and shifts the reaction equilibrium to product side. The main shortcoming of ODH and OCM processes is that, in the presence of gas phase oxygen, alkane and alkenes react further to form carbon oxides, leading to poor selectivity towards desired product; olefins. Although there is no consensus in the literature on the type of oxygen species active for selective oxidation of hydrocarbons to olefins via oxidative dehydrogenation and coupling reactions, it is generally accepted that oxygen in ionic form is more desirable than molecular oxygen. A solid electrolyte cell-type reactor offers a better selectivity control when operated in ion pump mode where the oxygen flux in the form of oxide ions to the surface could be controlled by applying an external current, while preventing the alkane/olefin molecules from encountering molecular oxygen.

To prove the concept, ethane/propane dehydrogenation and methane coupling activity experiments over perovskite-type oxide materials were conducted using both thermo- and electro-catalytic reaction systems. The preliminary results showed that olefin formation was more favored over complete oxidation in an electro-catalytic reaction system.

The activity/selectivity enhancement with the electro-catalytic route, however, comes with its own challenges including electrochemical reactor design and in-situ/operando characterization of electrocatalytic cells that require not only atmosphere/temperature control, but also electrical-bias control, posing new challenges.

Some perspectives gained over several decades of straddling thermo-catalytic and electro-catalytic studies will be shared.