Chemical reactions with zero or near-zero activation energy are well-documented in specific contexts, such as diffusion-controlled electron transfer and certain barrierless radical recombination steps.
The claim that certain chemical reactions occur with zero activation energy is supported by chemical physics literature on diffusion-controlled electron transfer and barrierless potential energy surface steps (e.g., papers 6 and 10), where activation barriers vanish under high electronic coupling or resonance conditions.