N2 emission in NO and N2O reduction on Rh(100) and Rh(110)

The angular distribution of desorbing N-2 was studied in both the thermal decomposition of N2O(a) on Rh(100) at 60-140 K and the steady-state NO (or N2O) + D-2 reaction on Rh(100) and Rh(110) at 280-900 K. In the former, N-2 desorption shows two peaks at around 85 and 110 K. At low N2O coverage, the desorption at 85 K collimates at about 66 degrees off normal towards the [001] direction, whereas at high coverage, it sharply collimates along the surface normal. In the NO reduction on Rh(100), the N-2 desorption preferentially collimates at around 71 degrees off. normal towards the [001] direction below about 700 K, whereas it collimates predominantly along the surface normal at higher temperatures. At lower temperatures, the surface nitrogen removal in the NO reduction is due to the process of NO(a)+N(a)-> N2O(a)-> N-2(g)+O(a). On the other hand, in the steady-state N2O + D-2 reaction on Rh(110), the N-2 desorption collimates closely along the [001] direction (close to the surface parallel) below 340 K and shifts to ca. 65 degrees off normal at higher temperatures. In the reduction with CO, the N-2 desorption collimates along around 65 degrees off normal towards the [001] direction above 520 K, and shifts to 45 degrees at 445 K with decreasing surface temperature. It is proposed that N2O is oriented along the [001] direction on both surfaces before dissociation and the emitted N-2 is not scattered by adsorbed hydrogen.