“…It is known from the literature that the oxidation of 1-butene to maleic anhydride occurs in at least two oxidation stages, namely from 1-butene to butadiene and from butadiene to maleic anhydride, although we have very little insight into the nature of the active sites (Seeboth et al, 1975; Nakamura et al, 1974; Ostroushko et al, 1969; Ai, 1977;Sunderland, 1976). On a MnMoO^c atalyst the existence of two distinct active sites involving two different oxygen species was hypothesized (Trifiro et al, 1973), but there were not sufficient experimental data to prove it.…”