Herein, Au_xCu alloy nanoparticles (NPs) embedded into TiO₂ nanocavity arrays (NCAs) were synthesized by e-Beam deposition and thermal dewetting. The periodically dispersed Au_xCu NPs displayed strong ultraviolet-visible light absorption through plasmonic resonance, especially after forming an Au_xCu–CuS core–shell heterostructure by sulfurization. When used as a photocatalyst for glycerol oxidation, the Au_xCu–CuS heterostructure showed high conversion efficiency (72%) and superb selectivity (66%) for dihydroxyacetone, even under neutral conditions and without an external heating source. The favorable photothermally enhanced oxidative activity originates from the synergistic core–shell and plasmonic effects in the Au_xCu–CuS@TiO₂ heterostructure. This work suggests a promising strategy for integrating the photothermal effect into the photocatalytic production of valuable organic compounds, therefore boosting solar energy conversion efficiency.