CO₂ hydrogenation to C1 chemicals has attracted significant interest due to the increasing demand for energy and global warming. Continuous efforts in the field of heterogeneous catalysis have revealed that CO₂ hydrogenation is structure-sensitive in monometallic catalysts. However, fundamental research into the structure-performance relationship in bimetallic catalysts is a big challenge because the well-defined bimetallic structures and the corresponding mechanism are more complex than those of monometallic ones. Here, with the construction of TiO₂ supported Ni–Ru bimetallic catalysts, evidenced by advanced microscopy characterizations, the alloyed and non-alloyed structures have been synthesised for hydrogenation. The in situ experiments show that the Ni–Ru bimetallic structures act like an ‘H-atom valve’ via control of the H₂ spillover, which can completely switch the CO₂ hydrogenation selectivity during the reaction. These findings bring a fundamentally new understanding of the selective hydrogenation on bimetallic nanocatalysts and the structure-performance relationship in controlling the ‘H-atom valve’ for many important chemical processes.