Atomically thin Pt nanolayers were synthesized on the surface of Mo₂TiC₂ MXenes and used for the catalytic dehydrogenation of ethane and propane into ethylene and propylene, two important chemicals for the petrochemical industry. As compared with Pt nanoparticles, the atomically thin Pt nanolayer catalyst showed superior coke-resistance (no deactivation for 24 h), high activity (turnover frequencies (TOFs) of 0.4–1.2 s⁻¹), and selectivity (> 95%) toward ethylene and propylene. The unique Pt nanolayer has a similar geometric surface to Pt nanoparticles, enabling the investigations of the electronic effect on the catalytic performance, where the geometric effect is negligible. It is found that the electronic effect plays a critical role in dehydrogenative product selectivity and catalyst stability. The metal–support interaction is found dependent on the substrate and metal components, providing wide opportunities to explore high-performance MXene-supported metallic catalysts.