Determination of ir extinction coefficients for linear- and bridged-bonded CO on supported palladium
Infrared spectra were obtained of CO adsorber on Pd dispersed on four supports: eta-Al/sub 2/O/sub 3/, SiO/sub 2/, SiO/sub 2/-Al/sub 2/O/sub 3/, and TiO/sub 2/. All catalysts were characterized by both H/sub 2/ and CO chemisorption which allowed the calculation of the surface coverages of both linearly adsorbed CO, which gives a band above 2000 cm/sup -1/, and the bridged-bonded form, which produces a band below 2000 cm/sup -1/. From these values, integrated absorbances, A, and extinction coefficients, epsilon, have been determined for each adsorbed species on Pd for the first time. For individual catalysts, absorbances and extinction coefficients were always much higher for the bridged-bonded CO than the linearly adsorbed CO, i.e., average values were A/sub b/ = 85 x 10/sup 7/ cm mol/sup -1/, A/sub 1/ = 3.3 x 10/sup 7/ cm mol/sup -1/, epsilon/sub b/ = 4.1 x 10/sup 6/ cm/sup 2/ mol/sup -1/, and epsilon/sub 1/ = 0.36 x 10/sup 6/ cm/sup 2/ mol/sup -1/. Because a specially designed ir reactor cell was utilized, spectra were also taken under steady-state CO hydrogenation reaction conditions to form CH/sub 4/. The Al/sub 2/O/sub 3/-, SiO/sub 2/-, and SiO/sub 2/-Al/sub 2/O/sub 3/-supported Pd catalysts still exhibited strong CO bands; however, Pd/TiO/sub 2/ wafers exhibiting SMSI (strong metal-support interactions) showed no detectable CO bands although they were the most active catalyst. Using the epsilon values obtained in this study, we estimated the maximum surface coverage on Pd to be less than 1% for the linear species and 0.1% for the bridged species.
- Research Organization:
- Pennsylvania State Univ., University Park
- DOE Contract Number:
- EG-77-S-02-4463
- OSTI ID:
- 6232257
- Journal Information:
- J. Phys. Chem.; (United States), Vol. 85:17
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CARBON MONOXIDE
CHEMISORPTION
HYDROGEN
PALLADIUM
CATALYTIC EFFECTS
ALUMINIUM OXIDES
CATALYST SUPPORTS
CATALYSTS
CHEMICAL BONDS
SILICON OXIDES
TITANIUM OXIDES
ALUMINIUM COMPOUNDS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
METALS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
SEPARATION PROCESSES
SILICON COMPOUNDS
SORPTION
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
400201* - Chemical & Physicochemical Properties