Atomically dispersed noble metal catalysts often exhibit high catalytic performances, but the metal loading density must be kept low (usually below 0.5%) to avoid the formation of metal nanoparticles through sintering. We report a photochemical strategy to fabricate a stable atomically dispersed palladium-titanium oxide catalyst (Pd-1/TiO2) on ethylene glycolate (EG)-stabilized ultrathin TiO2 nanosheets containing Pd up to 1.5%. The Pd-1/TiO2 catalyst exhibited high catalytic activity in hydrogenation of C=C bonds, exceeding that of surface Pd atoms on commercial Pd catalysts by a factor of 9. No decay in the activity was observed for 20 cycles. More important, the Pd-1/TiO2-EG system could activate H-2 in a heterolytic pathway, leading to a catalytic enhancement in hydrogenation of aldehydes by a factor of more than 55.