<p>Photocatalysis involves photogenerated charge carriers transferring to reactants via active sites. While carrier-reactant interactions are widely studied, carrier-site interactions remain overlooked. Here, we report a wavelength-gated in situ site regeneration strategy to improve catalyst stability. In photocatalytic CO₂ reduction, the Au/Ce_0.95Cu_0.05O_2-x solid-solution catalyst exhibited a high stability exceeding 48 h and a C₂H₆ production rate of 63.8 μmol g^–1 h^–¹. Notably, the catalyst initially deactivates rapidly under 375 nm light but can be reactivated under 535 nm light. In situ spectroscopy and theoretical simulation attributed this to an in situ redox process involving the active sites and reactants. Under 375 nm light, the Cu⁺-O₃-Ce site binds with dissociated O atoms from CO₂, transforming to an inactive Cu²⁺-O₄-Ce structure, which is subsequently reactivated by localized surface plasmon resonance hot electrons generated under 535 nm light. This work presents a universal strategy for designing catalysts with long-term stability.</p>