Tuning the Dissociative Action of Cationic Rh Clusters Toward NO by Substituting a Single Ta Atom

Modification of Rh chemical activity for decomposition of NO by alloying with Ta was studied by vibrational spectroscopy of gas-phase clusters, where one single Rh atom was substituted by Ta, with NO adsorbed. While NO adsorbs molecularly on pure Rh clusters, it was found to adsorb dissociatively on RhnTa+ (n = 2–8) with the O bound to the Ta on-top site. A reaction path for NO decomposition obtained by density functional theory calculations for octahedral Rh5Ta+ and Rh6+ suggests that the Ta oxygen affinity strongly reduces the energy barrier right before bond cleavage, facilitating NO dissociation. The trend is consistent with the Bell–Evans–Polanyi principle. The addition of other less oxophilic dopant atoms could plausibly enhance catalytic reactivity of Rh.