Theoretical study on the chemisorption of a hydrogen molecule on palladium
Interaction of a hydrogen molecule with palladium in the Pd-H/sub 2/ and Pd/sub 2/-H/sub 2/ systems is studied theoretically as a model for chemisorption and catalytic action of a metal surface. Sophisticated ab initio theories including electron correlations (CAS-MC-SCF, SAC and SAC-CI theories) are used for calculations of ground and excited states of the interacting systems. While a single Pd atom in the ground state shows affinity for the hydrogen molecule, it does not catalyze cleavage of the H-H bond, and a triangular adduct form is the stable geometry of the Pd-H/sub 2/ system. The lower lying excited states of the Pd atom are all repulsive. On the other hand, the Pd/sub 2/ system clearly shows catalytic activity toward hydrogen chemisorption. The H/sub 2/ molecule is adsorbed at about 1.5 A from the metal, and an equilibrium between molecular and dissociated adsorption forms is established, with the latter being more stable than the former by a few kilocalories/mole. The Pd-Pd bond is not weakened in this process, a fact related to the stability of the catalytic surface. The dangling bonds of the Pd surface and electron correlations play very important roles in this catalytic activity. The 4d orbitals of Pd are mainly involved, with the outer 5s orbital playing a secondary role. Without electron correlations, the dissociative adsorption is not explained even qualitatively. There is almost no chance for the excited states to participate in the catalytic process on Pd. This mechanism differs from that proposed for a Ni surface. Lastly, photoelectron spectra are theoretically calculated to explain some interacting features of the observed spectra for the hydrogen-palladium system.
- Research Organization:
- Kyoto Univ., Japan
- OSTI ID:
- 6509847
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 109:7
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
08 HYDROGEN
HYDROGEN
CHEMISORPTION
PALLADIUM
CATALYTIC EFFECTS
SORPTIVE PROPERTIES
SURFACE PROPERTIES
CALCULATION METHODS
CATALYSIS
CATALYSTS
CHEMICAL BONDS
EXCITED STATES
GROUND STATES
PHOTOELECTRON SPECTROSCOPY
THEORETICAL DATA
CHEMICAL REACTIONS
DATA
ELECTRON SPECTROSCOPY
ELEMENTS
ENERGY LEVELS
INFORMATION
METALS
NONMETALS
NUMERICAL DATA
PLATINUM METALS
SEPARATION PROCESSES
SORPTION
SPECTROSCOPY
TRANSITION ELEMENTS
400201* - Chemical & Physicochemical Properties
080201 - Hydrogen- Chemisorption Storage