Electron paramagnetic resonance study of the reactivity toward carbon monoxide and oxygen of O– ions adsorbed on silica-supported molybdenum catalysts

Abstract

Using the e.p.r. technique, the reaction at 77 K of an O^– radical, formed by N₂O adsorption on reduced MoO₃/SiO₂ samples, with CO or ¹³CO was followed, and it was possible to detect a CO^–₂ radical (g₁= 2.0029, g₂= 2.0016, g₃= 1.9974, A₁= 199 G, A₂= 240 G, A₃= 207 G) which was stable at room temperature. This species reacted with O₂ at 77 K to give rise to a radical of the type (O₂COO)^–(g₁= 2.0486, g₂= 2.0078, G₃= 2.0026, A_1C= OG, A_2C= 4.8 G, A_3C= 6 G, A_3OI= 140 G, A_3OII= 40 G). At 150 K, it disappeared irreversibly, generating an O^–₂ radical (g₁= 2.0175, g₂= 2.0097, g₃= 2.0040, A_3OI= 80 G, A_3OII= 70 G) similar to that formed by direct adsorption of oxygen on reduced MoO₃/SiO₂.