Pt3Zn1 and Pt1Zn1 intermetallic nanoparticles supported on SiO2 were synthesized by combining atomic layer deposition (ALD) of ZnO, incipient wetness impregnation (IWI) of Pt, and appropriate hydrogen reduction. The formation of Pt1Zn1 and Pt3Zn1 intermetallic nanoparticles was observed by both X-ray diffraction (XRD) and synchrotron X-ray absorption spectroscopy (XAS). STEM images showed that the 2-3 nm Pt-based intermetallic nanoparticles were uniformly dispersed on a SiO2 support. The relationships between Pt-Zn intermetallic phases and synthesis conditions were established. In situ XAS measurements at Pt L3 and Zn K edges during hydrogen reduction provided a detailed image of surface species evolution. Owing to a combined electronic and geometric effect, Pt1Zn1 exhibited much higher reactivity and stability than Pt3Zn1 and Pt in both the direct dehydrogenation and oxidative dehydrogenation of ethane to ethylene reactions.