Nanocatalysts are likely to contain undetected single-atom components, which may have been ignored but have significant effect in catalytic reactions. Herein, we report a catalyst composed of Mo single atoms (SAs) and MoO₂ nanoparticles (NPs) (Mo_SAs-MoO₂@NC), which is an exact model to understand how the SAs contribute to the nanocatalyst. Both experimental results and the density functional theory calculations reveal that Mo SAs on nitrogen-doped carbon provides the reaction zone for nitro reduction, while MoO₂ is the active site for decomposing hydrazine hydrate to produce H*. Thanks to the synergy between Mo SAs and MoO₂ NPs, this catalyst exhibits noble metal-like catalytic activity (100% conversion at 4 min) for the dechlorination-proof transfer hydrogenation. Additionally, the hydrogen migration on the catalyst is verified by the electrochemical tests in the absence of a hydrogen source. This work provides a model for further study on the coexistence of single atoms in nanoparticle catalysts.