Local reaction environments and their properties for ethene deuterogenation on the surfaces of SMSI catalysts

Abstract

Ethene deuterogenation and H₂–D₂ exchange reaction over Nb₂O₅-supported Rh and Ir catalysts have been investigated in relation to strong metal–support interaction (SMSI) phenomena. The activation energies for these reactions were considerably changed by high-temperature reduction of the catalyst in the case of Ir/Nb₂O₅, but were not modified in the case of Rh/Nb₂O₅. The change is ascribed to a reduction in the energy barrier for deuterium dissociation. The deuterium distribution in ethane formed during ethene deuterogenation was also investigated at various reaction temperatures and as a function of the reduction time of the catalyst. By studying the catalysts in their working state instead of by static adsorption measurements two kinds of active sites in different environments are suggested to exist on the surface of these catalysts in the SMSI states. One of these sites (site I) is on the bare metal surface and the other (site II) is on the perimeter of a migrating NbO_x island. The surface isotopic ratio of hydrogen during ethene deuterogenation is different at sites I and II. Site I, on which D₂ dissociates, acts as a deuterium supply for site II. A model for the deuterogenation of ethene on the SMSI catalysts is proposed.