Transient Kinetics during the Isothermal Reduction of NO by CO on Rh(111) As Studied with Effusive Collimated Molecular Beams

Abstract

The transient kinetics of the reaction between NO and CO on clean Rh(111) surfaces have been studied using molecular beams in conjunction with mass spectrometry detection. The changes in the partial pressures of the reactants (CO and NO) and products (N 2 and CO 2 ) as a function of time have been used as a measure of the evolution of the uptake and desorption rates, respectively, for temperatures between 350 and 1000 K and for NO:CO mixture ratios between 4:1 and 1:99. Post-mortem temperature programmed desorption (TPD) and CO titration experiments were also performed in order to estimate the surface coverages of atomic nitrogen and oxygen left on the Rh(111) surface by the gas mixture. Systematic variations were observed during the transition from the clean surface to the steady-state catalytic regime that correlate well with the overall reaction rates in the latter. Specifically, there is a time delay in the production of molecular nitrogen because of the need to build up a threshold atomic nitrogen coverage on the surface before the start of the desorption of N 2 . This atomic nitrogen coverage, as calculated by the time delay in the transient, corresponds to that estimated by TPD after the reaction, and displays a dependence on the NO:CO ratio in the reaction mixture, increasing at a given temperature as the beam becomes richer in CO. Initial sticking coefficients were also determined for both NO and CO in NO + CO mixtures as a function of surface temperature and beam composition. † Part of the special issue "Gabor Somorjai Festschrift".

Fabrication of an Effusive Molecular Beam Instrument for Surface Reaction Kinetics—CO Oxidation and NO Reduction on Pd(111) Surfaces

“…It is also clear from the above observations that the adsorption of NO on Pd(111) is dominating and hence an enrichment of NO over CO occurs compared to the gas phase [32]. A similar effect has already been observed by Gopinath and Zaera on Rh(111) [46]. The present results reveal a clear difference between adsorbate composition on the surface and beam compositions with respect to both the reactants.…”

“…At temperatures ‡525 K the displacement effect was very poor or not observed due to the very small steady state coverage of the reactants, particularly CO. The displacement of a chemisorbed species by another incoming species has been suggested and observed by few groups [42][43][44][45][46] for various catalytic reactions. It is also clear from the above observations that the adsorption of NO on Pd(111) is dominating and hence an enrichment of NO over CO occurs compared to the gas phase [32].…”

Surface science studies of selective catalytic reduction of NO: Progress in the last ten years

“…Studies of NO-CO reaction have been carried out on Pt(1 0 0) [30][31][32][33][34][35][36][37], Pt(1 1 1) [38], Pt(1 1 2) [39], Pd(1 0 0) [40], Pd(1 1 0) [41][42][43][44], Pd(1 1 1) [42,43,45,[46][47][48][49][50][51][52][53], Rh(1 0 0) [54], Rh(1 1 0) [54], Rh(1 1 1) [54][55][56][57][58][59][60][61][62][63][64][65], Ir(1 1 1) [66], Ir(2 1 1) [67], Cu(0 0 1) [68], Ag(1 1 1) [69], Pd/Cu(1 1 1) [48], Fe/Rh(1 0 0) [55], Rh/CeO x (1 1 1) [70], Pd/MgO(1 0 0) [71,72], Pt-Rh/TiO 2 (1 1 0) [73]...…”

“…These studies also play an important role in understanding the NO-CO reaction on metal crystal surfaces. In the past decade, nearly fifty percent of the publications dealing with the NO-CO reaction focus on theoretical modeling or a combination of theoretical modeling with experimental measurements [33,35,36,38,47,56,58,63,[82][83][84][85][86][87][88].…”

Lattice-gas study of the kinetics of catalytic conversion of NO–CO mixtures on rhodium surfaces

“…1,2 The catalytic reduction of NO to N 2 on rhodium has been heavily investigated both experimentally [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] and theoretically [22][23][24][25][26][27][28][29][30][31][32][33][34][35] for many years. The key steps of this reaction have long been thought to be the breaking of the N-O bond in NO upon chemisorption on the metal and the subsequent recombination of surface nitrogen atoms to form N 2 .…”