NO-CO activity and selectivity over a Pt[sub 10]Rh[sub 90](111) alloy catalyst in the 10-torr pressure range
- General Motors Research and Development Center, Warren, MI (United States)
The authors have studied the effects of temperature, NO conversion, and NO-CO ratio on the activity and selectivity of the NO-CO reaction over a Pt[sub 10]Rh[sub 90](111) surface. The NO-CO activity over the Pt[sub 10]Rh[sub 90](111) is very similar to that over the Rh(111) surface from 573 to 648 K in that both surfaces have the same E[sub a], reaction orders, products, and selectivities. The turnover numbers for the Pt[sub 10]Rh[sub 90](111) alloy are slightly lower than those for Rh(111), when compared on a per surface atom basis; however, the rates per surface Rh atom are virtually unchanged. This behavior suggests that the primary effect of Pt is to dilute the Rh surface atom concentration; however, it is equally consistent with electronic modification of all surface atoms. The surface composition remains essentially unchanged over the range of reaction conditions that were explored. The Pt[sub 10]Rh[sub 90](111) single crystal mimics the behavior of supported Pt-Rh catalysts is that both show high ([approximately]75%) selectivity for N[sub 2]O at low temperature, low conversion, or high NO-CO ratio and low or zero N[sub 2]O production at high temperature and high NO conversion. The conclusion is that the N[sub 2]O selectivity and the overall reaction rate are controlled by the NO adsorption/desorption equilibrium. Adsorbed NO strongly inhibits the NO dissociation reaction, keeping surface N coverages low. However, once the temperature is raised or the NO pressure lowered, surface NO coverages fall, accelerating the NO dissociation reaction and likewise increasing the N + N reaction. The authors conclude that these surface kinetics explain the curious N[sub 2]O selectivities observed during light-off of supported catalysts. 37 refs., 7 figs.
- OSTI ID:
- 7185266
- Journal Information:
- Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 146:2; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALLOYS
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
KINETICS
MILLER INDICES
NITRIC OXIDE
NITROGEN COMPOUNDS
NITROGEN OXIDES
OXIDES
OXYGEN COMPOUNDS
PLATINUM ALLOYS
PLATINUM METAL ALLOYS
REACTION KINETICS
RHODIUM ALLOYS
RHODIUM BASE ALLOYS