Activity-Stability Trade-Off for Photothermal Catalytic Methane Nonoxidative Coupling over Anatase Titania

Photothermal catalytic methane nonoxidative coupling (NOCM) is a potential way to utilize methane resources. Yet the distinct roles of light and heat in governing reaction kinetics and catalyst stability remain poorly understood. Our mechanistic study on the photocatalytic NOCM over the model anatase TiO₂(101) surface, employing first-principles-based microkinetic simulations, discloses that the activity of surface lattice oxygen significantly increases when it traps photogenerated holes, enabling the efficient C-H bond activation of methane. However, the sluggish hydrogen migration kinetics leads to hydroxylation of the lattice oxygen. This passivates the surface lattice oxygen for capturing photoexcited hole, thereby limiting methane C-H bond activation. Microkinetic simulations indicate elevated temperatures accelerate hydrogen migration and alleviate this kinetic bottleneck, thereby enhancing catalytic activity. However, photothermal catalysis can eliminate surface hydrogen poisoning; the elevated temperatures also accelerate the formation of water and oxygen vacancy, compromising the structural integrity of the catalyst and ultimately leading to deactivation. Guided by this understanding, we demonstrate that combining elevated temperature with a small amount of CO₂ can mitigate hydrogen accumulation and repair oxygen vacancies, thereby simultaneously improving methane coupling performance and catalyst stability.