Adsorption-desorption kinetics of H/sub 2/ from supported nickel catalysts
The adsorption-desorption interactions of hydrogen from a nickel-supported silica catalyst were studied by pulsed chemisorption and temperature-programmed desorption (TPD) techniques incorporating on-line mass spectrometric detection in a flow system. Pulsed chemisorption results of the metal surface area agree with results from more conventional static measurements. A combination of pressure pulse analysis and flow rate variation allowed the adsorption kinetics to be determined as (1 to theta)/sup 2/, where theta is the fractional coverage. The activation energy for adsorption, E/sub a/, is nearly zero. TPD spectra showed a general trend of second-order desorption kinetics with a shift in peak temperature to lower temperatures as the coverage was increased. After experimentally eliminating all transport considerations which would have caused shaping of the spectra, a self-consistent analysis of the desorption rate isotherms, characteristic plots, and lineshapes of the spectra led to the conclusion that free readsorption of hydrogen dominated during the desorption. The activation energy, E/sub d/, is 89 kJ/mole at low coverage and 55 kJ/mole at higher coverages. The falloff in E/sub d/ with theta occurs at a critical coverage which is strongly dependent on the sample weight. When the role of readsorption was clarified and provided that the catalyst bed length approached differential bed requirements, the variation in the activation energy with coverage agreed quantitatively with results obtained from single-crystal experiments. The compensation effect in the desorption rate constant was also observed. 12 figures, 3 tables.
- Research Organization:
- Syracuse Univ., NY
- OSTI ID:
- 5718325
- Journal Information:
- J. Catal.; (United States), Vol. 73:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
HYDROGEN
ADSORPTION
DESORPTION
NICKEL
SORPTIVE PROPERTIES
ACTIVATION ENERGY
CATALYST SUPPORTS
CATALYSTS
CHEMISORPTION
FLOW RATE
MASS SPECTROSCOPY
REACTION KINETICS
SILICA
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
ENERGY
KINETICS
METALS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
SEPARATION PROCESSES
SILICON COMPOUNDS
SILICON OXIDES
SORPTION
SPECTROSCOPY
SURFACE PROPERTIES
TRANSITION ELEMENTS
080800* - Hydrogen- Properties & Composition