Surface-nitrogen removal in NO and N2O reduction on Pd(1 1 0): Angular distribution studies of desorbing products

This paper is a report of angle-resolved product desorption measurements in the course of catalyzed NO and N2O reduction on Pd(1 1 0). Surface-nitrogen removal processes show different angular distributions, i.e. normally directed N2 desorption takes place in process (i) 2N(a) → N2(g). Highly inclined N2 desorption towards the [0 0 1] direction is induced in process (ii) N2O(a) → N2(g) + O(a). N2O or NH3 desorption follows the cosine distribution characterizing the desorption after the thermalization in process (iii) N2O(a) → N2O(g) or (iv) N(a) + 3H(a) → NH3(a) → NH3(g). Thus, a combination of the angular and velocity distributions provides the analysis of most of surface-nitrogen removal processes in the course of catalyzed NO reduction. At temperatures below 600 K, processes (ii) and (iii) dominate and process (iv) is enhanced at H2 pressures higher than NO. Process (i) contributes significantly above 600 K. Only three processes except for NH3 formation are operative when CO is used. Only process (ii) was observed in a steady-state N2O + CO (or H2) reaction.