A catalytic membrane reactor using ion-oxide conductors as catalysts is experienced in selective oxidative dimerization of propene to C-6-dimers. Structural and textural properties, catalytic and non-catalytic reactivities of M-doped Bi2O3 (M = La, Ce, Eu, Er, V, Nb) are studied. TGA experiments show that dopants increase the rates of reduction and reoxidation of Bi2O3, but that the reoxidation of the catalysts is rate limiting. During catalysis, the best yields in 1,5-hexadiene and benzene are obtained with cerium-doped Bi2O3.