Chemical environments around active sites and reaction mechanisms for deuterium–acrolein reaction over Ir/Nb2O5 in normal and SMSI states

Abstract

Deuteration and hydrogenation of acrolein over Ir/Nb₂O₅ reduced at 473 (normal state) or 773 K (SMSI state) were investigated by kinetics and tracer techniques in order to understand chemical environments around active sites in the working state and to clarify the reaction mechanism involving electronic and geometric factors. The reaction rates for each product as a function of reduction time of catalyst together with the isotope distributions in acrolein, allyl alcohol and propanal demonstrated that deuterium dissociates only on bare metal sites (site I); propanal and 1-d₁-acrolein are formed on site I, while allyl alcohol is formed on both site I and the peripheral sites of migrated NbO_x islands (site II), although through the different intermediates of η²- and η⁴-species, respectively, and 3-d₁-acrolein is formed on site II. The two active sites in SMSI state are also characterized with different surface D/H ratio around them during catalytic reaction.