Interaction of MoO3 with propene at the temperature range 420-520 K results
in the appearance of several EPR signals. Four of them have been assigned
to different Mo(v) centres, one to localised conduction electrons. The anal
ysis of the signals' parameters and the sequence of their appearance allows
the conclusion that the allyl species formed in the first stage of interac
tion are adsorbed in a certain distance from the simultaneously created Mo(
v). This is an important finding, modifying the existing hypotheses on the
reaction mechanism. In the next stage of reduction the precursors of shear
structures are formed due to the removal of lattice oxygen by the desorbing
oxidation products.