Competing pathways for isocyanate loss from Cu(0 0 1) with co-adsorbed oxygen

Cu(0 0 1)-bound isocyanate species (NCO(a)) have been prepared with two distinct methods. Isocyanic acid (HNCO) exposures at room temperature resulted in adsorbed NCO(a) alone. The exposure of Cu(0 0 1) to cyanogen (C2N2) and O2 leads to surfaces displaying co-adsorbed oxygen (O(a)), cyanide (CN(a)), and NCO(a) species. O2 exposure of submonolayer NCO/Cu(0 0 1), followed by brief annealing at 473 K, initiated NCO(a) oxidation, giving rise to CO2(g) desorption and a surface-bound atomic N(a) species. CO2(g) evolution was observed over a wide range of initial O(a) coverages. In contrast, comparable thermal treatments of CN + O + NCO/Cu(0 0 1) samples, at 473 K, yield both CO(g) and CO2(g). Both TPRD and XPS studies of pre- and post-annealed surfaces indicated the two gaseous products. The co-adsorption of CN(a) promotes the dissociation of NCO(a) into CO(g) and N(a), and dissociation can become the dominant means for NCO(a) removal.