In-situ X-ray absorption spectroscopy studies of hydride and carbide formation in supported palladium catalysts

Journal Article · Thu Oct 07 04:00:00 EDT 1993 · Journal of Physical Chemistry; (United States)

DOI:https://doi.org/10.1021/j100142a018· OSTI ID:5651809

McCaulley, J A ^[1]

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1. Robert L. Mitchell Technical Center, Summit, NJ (United States)

Extended X-ray absorption fine structure (EXAFS) spectroscopy as used to characterize hydride and carbide phases in supported Pd catalysts. Transmission EXAFS measurements were made at room temperature on 5% Pd/C and 5% Pd/[gamma]-Al[sub 2]O[sub 3] catalysts. Combined EXAFS and transmission electron microscopy (TEM) results indicate that the average Pd particle diameter is 26 [+-] 8 Angstroms (or Pd dispersion is approximately 45%) in both catalysts. Supported Pd particles in air-exposed catalysts were found to be approximately 98% converted to a disordered Pd oxide; the remaining Pd is in metallic cores (average diameter is approximately 6 Angstroms) inside the oxidized Pd particles. Catalysts were reduced in situ and cooled to 25[degrees]C in H[sub 26] (partial pressure of 26 Torr), yielding a hydride phase with a lattice expansion of 2.2 [+-] 0.2%. The stoichiometry of the hydride phase, PdH[sub x] (x to [approximately] 0. 44), is consistent with previous reports of decreased H[sub 2] sorption capacity, relative to bulk Pd, in supported Pd catalysts. Decomposition of the hydride phase yielded metallic Pd particles with a first-shell Pd-Pd coordination number of 9 [+-] 1. Reaction of the reduced 5% Pd/C catalyst with 1% C[sub 2]H[sub 4]/ Ar at 150[degrees]C for 20 min generates a Pd carbide phase with an average Pd-Pd distance 1.2% larger than that in Pd metal. The PdC[sub x] phase has a maximum carbon content, x to approximately 0.06, about half that of bulk PdC[sub x[prime]] x to approximately 0.13. 44 refs., 10 figs., 6 tabs.

• DOE Contract Number: FG05-89ER45384; AC02-76CH00016
• OSTI ID: 5651809
• Journal Information: Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 97:40; ISSN JPCHAX; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400102 -- Chemical & Spectral Procedures
400201* -- Chemical & Physicochemical Properties
ABSORPTION SPECTROSCOPY
ACTIVATED CARBON
ADSORBENTS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CARBIDES
CARBON
CARBON COMPOUNDS
CATALYST SUPPORTS
CATALYSTS
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
FINE STRUCTURE
HYDRIDATION
HYDRIDES
HYDROGEN COMPOUNDS
METALS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PALLADIUM
PALLADIUM CARBIDES
PALLADIUM COMPOUNDS
PALLADIUM HYDRIDES
PLATINUM METALS
SPECTROSCOPY
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
X-RAY SPECTROSCOPY