Promoted activity of annealed Rh nanoclusters on thin films of Al₂O₃/NiAl(100) in the dehydrogenation of Methanol-d₄

Annealed Rh nanoclusters on an ordered thin film of Al₂O₃/NiAl(100) were shown to exhibit a promoted reactivity toward the decomposition of methanol-d₄, under both ultrahigh vacuum and near-ambient-pressure conditions. The Rh clusters were grown with vapor deposition onto the Al₂O₃/NiAl(100) surface at 300 K and annealed to 700 K. The decomposition of methanol-d₄proceeded only through dehydrogenation, with CO and deuterium as products, on Rh clusters both as prepared and annealed. Nevertheless, the catalytic reactivity of the annealed clusters, measured with the production of either CO or deuterium per surface Rh site from the reaction, became at least 2-3 times that of the as-prepared ones. The promoted reactivity results from an altered support effect associated with an annealing-induced mass transport at the surface. Our results demonstrate a possibility to practically prepare reactive Rh clusters, regardless of the cluster size, that can tolerate an elevated reaction temperature, with no decreased reactivity.