Surface intermediates during the catalytic reduction of NO on rhodium catalysts: a kinetic inference

Isothermal kinetic studies on the reduction of NO by CO on Rh(1 1 1) single -crystal surfaces, performed under vacuum by using collimated effusive mole cular beams, have provided information on the coverages and nature of the s urface intermediates involved in that reaction under catalytic conditions. Three major conclusions were reached. First, the optimum rate of reaction i s achieved when the steady-state coverages of NO and CO on the surface reac h the 1:1 stoichiometric ratio. The surface coverages are controlled by a s ynergistic balance between the composition of the gas and the surface tempe rature: higher temperatures tend to require higher CO:NO ratios. Second, un der optimum conditions the surface of the catalyst is mostly covered with a tomic nitrogen. This nitrogen appears to cluster in islands, and further co nversion to molecular nitrogen takes place preferentially at their peripher y. Finally, the formation of molecular nitrogen under catalytic conditions is likely to involve the formation of a N-NO intermediate. Evidence for the se conclusions is provided. (C) 2001 Elsevier Science B.V. All rights reser ved.