Ageing of fresh and used Ca-Sr-cuprate-based catalysts

O− spin bags formation in (CeO2)0.75(La2CuO4)0.24 catalyst after extended use for reduction of NO by CO

“…Low-field (g = 3) EPR lines have been already reported by us with calcined Ca2CuO3 [4], and SrCuO2 [5] (the latter just at high detection temperature), as well as with other Ca-Sr-cuprates, but only after catalytic use for toluene oxidation [6], or with unused sample but after one year ageing [7]. Those lines were interpreted as due to Strongly Interacting Dipoles (SID).…”

“…Those lines were interpreted as due to Strongly Interacting Dipoles (SID). In fact it is well known [4][5][6][7][8][9] that, when two unpaired spins S ; and SS interact with a dipolar energy Si D S^ = ST D ST (with ST = S, + S^) even overcoming the electron Zeeman energy, SID form, generating low-field EPR lines (in many cases with apparent g -3) moving towards higher fields both at decreasing real g values and at increasing dipolar constant D.…”