Preferential oxidation of carbon monoxide in hydrogen using zinc oxide photocatalysts promoted and tuned by adsorbed copper ions

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.

Graphical abstractPhoto-PROX: Preferential oxidation of CO in H2 by photocatalysis using Cu(II) on spheroidal ZnO as the catalyst.Figure optionsDownload full-size imageDownload high-quality image (183 K)Download as PowerPoint slideHighlights► Spheroidal (22 nm × 47 nm) and rod-like ZnO (80 nm × 443 nm) were synthesized. ► 0.5% of Cu2+-adsorbed spheroidal ZnO was a semiconductor with bandgap of 3.17 eV. ► Cu–spheroidal ZnO was most effective for photo-PROX of CO in H2. ► Cu–ZnO reduced 63 Pa of CO to 2.3 mPa (0.35 ppm) in 6.3 kPa of H2 for 5 h. ► CuII trapped photogenerated electrons and would oxidize formate species to CO2.