Direct Nonoxidative Methane Coupling to Ethylene over Gallium Nitride: A Catalyst Regeneration Study

Abstract

The abundance of methane in natural and shale gases creates the need to develop processes for the direct conversion of methane to olefins, aromatics, and hydrogen. In this work, the regeneration capability and reusability of gallium nitride (GaN) catalysts for the direct nonoxidative methane activation with subsequent coupling to ethylene were studied. Unsupported GaN and silica-supported GaN/SBA15 catalysts were synthesized and evaluated. Each catalyst was subjected to two different regeneration methods. In the first method, the used catalysts were regenerated with air at 500–550 °C and reused several times. Due to the slight oxidation of the surface GaN to Ga2O3, the ethylene yield decreased by 16% after five cycles. The second method included an intermediate renitridation step after air regeneration to convert the surface Ga2O3 back to GaN. By doing so, the ethylene yield remained constant over multiple cycles.