Local coordination environments of isolated metal atoms in single-atom catalysts (SACs) play decisive roles for their catalytic performance. By varying the morphology and P and N heteroatom doping of the CeO₂ support, here we showed that the activity of Pt single atoms on spherical CeO₂ is about 7 times higher than that on CeO₂ nanorods in hydrogenation of phenylacetylene. Doping the spherical CeO₂ support using N is more effective than using P, and could enhance the activity by another 3.3 times, which was 2.6-times even higher than that of spherical CeO₂ supported Pt clusters. Diffuse reflectance infrared Fourier transform spectroscopy of chemisorbed CO and X-ray photoelectron spectroscopy showed that N doping induced an increase of the electron density of Pt single atoms, opposite to the effect of P doping. H–D exchange and temperature-programmed reduction of hydrogen revealed that a large enhancement of hydrogen dissociation activity and hydrogen spillover by N doping are both essential for promoting the activity for catalytic hydrogenation.