Monte Carlo simulations of temperature-programmed and isothermal desorption from single-crystal surfaces
- California Inst. of Tech., Pasadena, CA (USA). Dept. of Chemical Engineering Lawrence Berkeley Lab., CA (USA)
The kinetics of temperature-programmed and isothermal desorption have been simulated with a Monte Carlo model. Included in the model are the elementary steps of adsorption, surface diffusion, and desorption. Interactions between adsorbates and the metal as well as interactions between the adsorbates are taken into account with the Bond-Order-Conservation-Morse-Potential method. The shape, number, and location of the TPD peaks predicted by the simulations is shown to be sensitive to the binding energy, coverage, and coordination of the adsorbates. In addition, the occurrence of lateral interactions between adsorbates is seen to strongly effect the distribution of adsorbates is seen to strongly effect the distribution of adsorbates on the surface. Temperature-programmed desorption spectra of a single type of adsorbate have been simulated for the following adsorbate-metal systems: CO on Pd(100); H{sub 2} on Mo(100); and H{sub 2} on Ni(111). The model predictions are in good agreement with experimental observation. TPD spectra have also been simulated for two species coadsorbed on a surface; the model predictions are in qualitative agreement with the experimental results for H{sub 2} coadsorbed with strongly bound atomic species on Mo(100) and Fe(100) surfaces as well as for CO and H{sub 2} coadsorbed on Ni(100) and Rh(100) surfaces. Finally, the desorption kinetics of CO from Pd(100) and Ni(100) in the presence of gas-phase CO have been examined. The effect of pressure is seen to lead to an increase in the rate of desorption relative to the rate observed in the absence of gas-phase CO. This increase arises as a consequence of higher coverages and therefore stronger lateral interactions between the adsorbed CO molecules.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- Sponsoring Organization:
- DOE/ER
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6562078
- Report Number(s):
- LBL-29484; ON: DE91001740
- Country of Publication:
- United States
- Language:
- English
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360104 -- Metals & Alloys-- Physical Properties
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
656002 -- Condensed Matter Physics-- General Techniques in Condensed Matter-- (1987-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ADSORPTION
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTION KINETICS
DESORPTION
DIFFUSION
ELEMENTS
IRON
ISOTHERMAL PROCESSES
KINETICS
METALS
MOLYBDENUM
MONTE CARLO METHOD
NICKEL
OXIDES
OXYGEN COMPOUNDS
PALLADIUM
PLATINUM METALS
PRESSURE EFFECTS
REACTION KINETICS
RHODIUM
SORPTION
SURFACES
TEMPERATURE DEPENDENCE
THERMAL DIFFUSION
TRANSITION ELEMENTS