Electron paramagnetic resonance investigation of oxygen photoadsorption and its reactivity with carbon monoxide on titanium dioxide: the O 3? 3 species

Abstract

Oxygen absorbed on TiO2 when subjected to u.v. irradiation gives rise to three different paramagnetic species. The first species, A, has been identified as O–2(g1= 2.021, g2= 2.009 and g3= 2.001 and C1≈C2≈ 0 Oe, C3= 77 Oe for 17O hyperfine spliting), the second species, C, as O–3(g1= 2.014, g2= 2.009 and g3= 2.003, no detected hyperfine lines due to 17O) and the third, B, as O3–3(g∥= 2.008 and g⊥= 2.001, no detectable hyperfine lines due to 17O). The latter species reacts readily with CO at 77 K and gives rise to species D, identified as OI–OII–CO–III according to the reaction: O3–3+ CO → O2–latt.+ O—O—CO– where the two directly bonded oxygen atoms originate from the absorbed molecular oxygen. The e.p.r. parameters of species D are : g1= 2.0465, g2= 2.006, g3= 2.001, C1≃ 6 Oe ± 0.5C2≈C3≈ 4 Oe ± 0.5 for 13C hyperfine interaction, CI1≈CI2≈ 0 and CI3= 104 Oe, CII1C≈II2 0 and CII3≃ 42.5 Oe and CIII1≈CIII2≈CIII3≈ 0 for 17O hyperfine splitting constants of the three oxygen nuclei. It is mainly the characterization of species, D, which enables us to postulate the nature of species, B.