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

Abstract

The angular distribution of desorbing N₂ was studied in both the thermal decomposition of N₂O(a) on Rh(100) at 60–140 K and the steady-state NO (or N₂O) + D₂ reaction on Rh(100) and Rh(110) at 280–900 K. In the former, N₂ desorption shows two peaks at around 85 and 110 K. At low N₂O coverage, the desorption at 85 K collimates at about 66° 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 N₂ desorption preferentially collimates at around 71° 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) → N₂(g) + O(a). On the other hand, in the steady-state N₂O + D₂ reaction on Rh(110), the N₂ desorption collimates closely along the [001] direction (close to the surface parallel) below 340 K and shifts to ca. 65° off normal at higher temperatures. In the reduction with CO, the N₂ desorption collimates along around 65° off normal towards the [001] direction above 520 K, and shifts to 45° 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 N₂ is not scattered by adsorbed hydrogen.