C-N Coupling in Reactions between Atomic Nitrogen and Ethylene on Rh(111)

Reactions between adsorbed atomic nitrogen and ethylene on Rh(111) have been investigated by temperature-programmed reaction spectroscopy (TPRS), secondary ion mass spectrometry (SIMS), and work function measurements. Coadsorption of a small amount of ethylene to 0.10 monolayer of atomic nitrogen results in the formation of a surface cyanide species, which is detected by SIMS through the Rh2CN+ cluster ion. Cyanide formation has been followed by measuring the decrease of the atomic nitrogen and carbon coverages and the accompanied increase in the CN coverage in temperature-programmed SIMS experiments. The CN formation kinetics is described by a preexponential factor and an activation energy of 1011(1 s-1 and 111 ( 10 kJ/mol, respectively. In the absence of surface hydrogen, CN groups are stable up to 700 K. CN decomposition results in reaction-limited desorption of N2 with a maximum at 800 K and is described by a preexponential factor and an activation energy of 1013(1 s-1 and 210 ( 15 kJ/mol. Coadsorption of large amounts of ethylene to 0.10 monolayer of Nads results in the desorption of almost all nitrogen in the form of HCN between 500 and 700 K. Cyanogen was also observed as a reaction product although the selectivity was small, 3 % at maximum. Work function measurements indicate that surface cyanide is present as a negatively charged species on the Rh(111) surface