In Situ Environmental STEM Study of the MoVTe Oxide M1 Phase Catalysts for Ethane Oxidative Dehydrogenation
Résumé
In situ environmental STEM-(HA)ADF has been used to characterize a light alkane mild oxidation catalyst corresponding to a MoVTeO M1 phase. The results obtained show that there is almost no structure disordering under reaction conditions closed to ethane oxidative dehydrogenation catalytic reactions: i.e., 350 degrees C under 1 mbar of a 30/15/55 O-2/C2H6/N-2, gas mixture. They further demonstrate that {Te-O-x} chains present in the hexagonal channels of the structure participate in the redox process of the catalyst and constitute a preferential pathway for the reoxidation of the surface catalytic active sites. Upon reduction it is proposed that labile oxygens are removed from the chains, leading to a high content of Te4+-O3E and Te2+O2 species and a displacement of the tellurium position toward the atomic columns between the two hexagonal channels. This process is proposed to involve the reduction of tellurium only under the strongest reducing conditions. The study also shows a constant ending of the [001] zone by {Mo(Mo)(5)} structural units and the bulk catalytic sites generally proposed should not appear on the facets of this type of rod.