Preferential oxidation of CO (63 Pa) and O2 (76 Pa) in H2 (6.3 kPa) using spheroidal ZnO nanoparticles (22 nm × 47 nm) converted 52% of CO into CO2 and selectivity to CO2 was 92 mol% under UV–visible light for 5 h.  When 0.5 wt% of Cu2+ was adsorbed on ZnO, 91% of CO was converted into CO2 with a selectivity of 99 mol% under UV–visible light for 3 h.  CO (63 Pa) was photocatalytically decreased to 2.3 mPa (0.35 ppm) in O2 (150 Pa) and H2 (6.3 kPa) for 5 h with a selectivity of 94 mol%.  As evident from a XANES peak at 8983.1 eV, the surface CuII sites trapped photogenerated electrons.  Furthermore, O2-derived species were reduced by accepting electrons from CuI and protons from the neighboring formate species, as indicated by the FT–IR peaks at 2985, 2879, 1627, 1587, and 1297 cm–1.