Kinetics of CO oxidation by N[sub 2]O over Rh(111)

Journal Article · Sun Nov 01 04:00:00 EST 1992 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1016/0021-9517(92)90007-5· OSTI ID:5517188

Belton, D N; Schmieg, S J ^[1]

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1. General Motors Research Labs., Warren, MI (United States)

The authors have studied, for the first time, the reaction of CO with N[sub 2]O over a Rh(111) catalyst at pressures between 1 and 20 Torr in an apparatus that couples a moderate pressure reaction with an ultrahigh vacuum analysis chamber. Using 4 Torr of CO and 4 Torr of N[sub 2]O between 570 and 670 K, the authors measured an apparent activation energy (E[sub a]) of 40.0 kcal/mol. By varying the reactant pressures (T = 623 K), it was determined that the reaction orders are +1.1 in N[sub 2]O pressure and [minus]1.2 in CO pressure. Both E[sub a] and the reaction order are in good agreement with previously reported measurements over alumina supported Rh particles. Kinetic modeling of the data suggests that CO and N[sub 2]O compete for a limited number of vacant sites on a surface where [Theta][sub CO] [ge] 0.9 ML. Under these conditions, the rate limiting step is N[sub 2]O dissociation. It is estimated, based on the model, that the barrier for N[sub 2]O dissociation (E[sup N[sub 2]O][sub diss]) is 17.5 kcal/mol. The model also predicts that the N[sub 2]O sticking coefficient (S[sub n[sub 2]O]) must be greater than 0.005. These measurements show that there is excellent agreement between Rh(111) and supported Rh reaction kinetics with regards to both E[sub a] and the CO pressure dependence. These experimental results add still another reaction to the growing list of cases where single crystals are excellent models for more practical supported catalysts. Further, modeling of these results allows us to estimate two previously unknown quantities, S[sub N[sub 2]O] and E[sup N[sub 2]O][sub diss]. 24 refs., 3 figs., 1 tab.

• OSTI ID: 5517188
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 138:1; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

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