Steady-state CO oxidation kinetics over the Pd(100) single crystal surface and the c(2 times 2)-Sn/Pd(100) bimetallic surface alloy
- Los Alamos National Lab, NM (United States)
The kinetic rates for CO oxidation have been measured in a high pressure/ultra-high vacuum surface analysis chamber over the temperature range of 443-673 K and the pressure range of 0.3-108 Torr. An Arrhenius activation energy of 22 kcal/mole was measured for CO oxidation at the Pd(100) single crystal surface. Furthermore, the reaction order for the CO was found to decrease from {minus}0.2 to {minus}0.9 as the pressure was lowered from 16 to 1 Torr CO, and the O{sub 2} reaction order was found to increase from 0.6 to 1.0 at CO pressures of 16 and 1 Torr, respectively. These changes are attributed to the dramatic variation in heat of adsorption seen on the Pd(100) surface (34 to less than 20 kcal/mole at saturation coverage (nonlinear function)). The kinetic behavior of the c(2 {times} 2)-Sn/Pd(100) bimetallic surface alloy was similarly studied and the activation energy for the CO oxidation reaction was found to be 12 kcal/mole. The surface alloy was ascertained to have catalytic reaction orders for CO and O{sub 2} of 0.2 and 0.1, respectively. This is attributed to an increase in the oxygen surface coverage in the form of SnO{sub x} (x = 1-2) atop the Pd(100) template. Possible roles that the SnO{sub x} plays in accelerating this reaction are suggested. The surfaces were also characterized by Auger electron spectroscopy, low energy electron diffraction, and thermal desorption mass spectroscopy prior to and following high pressure catalytic reactions.
- OSTI ID:
- 7141591
- Journal Information:
- Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 133:1; ISSN 0021-9517; ISSN JCTLA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
330702 -- Emission Control-- Carbon Monoxide
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ACTIVATION ENERGY
ADSORPTION HEAT
ALLOYS
AUGER ELECTRON SPECTROSCOPY
BIMETALS
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON MONOXIDE LASERS
CARBON OXIDES
CATALYTIC CONVERTERS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COHERENT SCATTERING
DESORPTION
DIFFRACTION
ELECTRON DIFFRACTION
ELECTRON SPECTROSCOPY
ELEMENTS
ENERGY
ENTHALPY
EQUIPMENT
GAS LASERS
KINETICS
LASERS
LOW PRESSURE
MASS SPECTROSCOPY
MEDIUM VACUUM
METALS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PALLADIUM
PALLADIUM ALLOYS
PHYSICAL PROPERTIES
PLATINUM METAL ALLOYS
PLATINUM METALS
POLLUTION CONTROL EQUIPMENT
PRESSURE DEPENDENCE
REACTION KINETICS
SCATTERING
SORPTION
SPECTROSCOPY
STEADY-STATE CONDITIONS
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
THERMODYNAMIC PROPERTIES
TIN ALLOYS
TIN COMPOUNDS
TIN OXIDES
TRANSITION ELEMENTS