CO + O/sub 2/ reaction on Rh(111): steady-state rates and adsorbate coverages

Journal Article · Thu Nov 06 04:00:00 EST 1986 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100281a027· OSTI ID:6952989

Schwartz, S B; Schmidt, L D; Fisher, G B

Steady-state kinetics of CO oxidation on clean Rh(111) were measured over a wide range of CO and O/sub 2/ gas-phase compositions and surface temperatures for pressures between 10/sup -6/ and 10/sup -/( Torr. Coverages were measured by XPS during steady-state reaction. Below 425 K the reaction rate increases with temperature with an activation energy of 20 kcal/mol, while above 450 K the rate decreases with temperature with an activation energy of -7 kcal/mol. At low temperatures and in excess CO, the reaction rate is proportional to P/sub O/sub 2//P/sub CO//sup -1/, while in excess O/sub 2/ and at high temperatures the reaction rate is negative order in P/sub O/sub 2// and more than first order in P/sub CO/. Near stoichiometric reactant ratios XPS shows that CO is the dominant adsorbed species below 400 K, while from 425 to 900 K the surface is nearly saturated with oxygen. Experimental rates and coverages are fit qualitatively by using a simple Langmuir-Hinshelwood model assuming competitive adsorption, although adsorption parameters for CO and O/sub 2/ are not in agreement with clean surface values. Modified Langmuir-Hinshelwood models involving strong inhibition of oxygen adsorption by adsorbed CO, either through coverage-dependent sticking coefficients or a dependence of the heat of adsorption of oxygen on the CO coverage, give good agreement with UHV parameters, measured CO and oxygen coverages, and reaction rates.

• Research Organization: Univ. of Minnesota, MN
• OSTI ID: 6952989
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 90:23; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
500200 -- Environment
Atmospheric-- Chemicals Monitoring & Transport-- (-1989)
54 ENVIRONMENTAL SCIENCES
ACTIVATION ENERGY
ADSORPTION
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DATA
ELECTROMAGNETIC RADIATION
ELECTRON SPECTROSCOPY
ELEMENTS
ENERGY
EXPERIMENTAL DATA
FLUIDS
GASES
INFORMATION
IONIZING RADIATIONS
KINETICS
MATHEMATICAL MODELS
METALS
NONMETALS
NUMERICAL DATA
OXIDATION
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PHOTOELECTRON SPECTROSCOPY
PLATINUM METALS
QUANTITY RATIO
RADIATIONS
REACTION KINETICS
RHODIUM
SORPTION
SPECTROSCOPY
STEADY-STATE CONDITIONS
STOICHIOMETRY
SURFACE PROPERTIES
TEMPERATURE DEPENDENCE
TRANSITION ELEMENTS
ULTRAHIGH VACUUM
X RADIATION