The reaction network of the ethene-to-propene (ETP) reaction over Ni/AlMCM-41 catalysts was studied. This reaction consists of the dimerization of ethene, the isomerization of 1-butene, and the metathesis of ethene and 2-butene to propene. This work focused on the latter. ETP experiments followed by in situ diffuse reflectance infrared Fourier transform spectroscopy were carried out. Metathesis activities were evaluated by the isomerization of butenes, the metathesis of ethene and 2-butene, and the retro-metathesis of propene. Metathesis activities of Ni/AlMCM-41 catalysts were not observed. Thus, a conjunct polymerization of ethene to propene is proposed.