Plasmonic "antenna reactor" alloys, consisting of a plasmonic material doped with a catalytically active metal, show great promise for efficient photocatalysis. However, while simple, intuitive, and approximate design principles such as the Sabatier principle have been developed for thermal and electrocatalysis, similar design principles for plasmonic catalysts remain elusive. Here, we develop these simple design principles by using real-time, time-dependent density functional theory to study small molecule activation (CH