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

Abstract

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 generatesmore » 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.« less

Authors:
 [1]
  1. Robert L. Mitchell Technical Center, Summit, NJ (United States)
Publication Date:
OSTI Identifier:
5651809
DOE Contract Number:  
FG05-89ER45384; AC02-76CH00016
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry; (United States)
Additional Journal Information:
Journal Volume: 97:40; Journal ID: ISSN 0022-3654
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CATALYSTS; HYDRIDATION; PALLADIUM; PALLADIUM CARBIDES; ABSORPTION SPECTROSCOPY; X-RAY SPECTROSCOPY; PALLADIUM HYDRIDES; ACTIVATED CARBON; ALUMINIUM OXIDES; CATALYST SUPPORTS; FINE STRUCTURE; ADSORBENTS; ALUMINIUM COMPOUNDS; CARBIDES; CARBON; CARBON COMPOUNDS; CHALCOGENIDES; CHEMICAL REACTIONS; ELEMENTS; HYDRIDES; HYDROGEN COMPOUNDS; METALS; NONMETALS; OXIDES; OXYGEN COMPOUNDS; PALLADIUM COMPOUNDS; PLATINUM METALS; SPECTROSCOPY; TRANSITION ELEMENT COMPOUNDS; TRANSITION ELEMENTS; 400201* - Chemical & Physicochemical Properties; 400102 - Chemical & Spectral Procedures

Citation Formats

McCaulley, J A. In-situ X-ray absorption spectroscopy studies of hydride and carbide formation in supported palladium catalysts. United States: N. p., 1993. Web. doi:10.1021/j100142a018.
McCaulley, J A. In-situ X-ray absorption spectroscopy studies of hydride and carbide formation in supported palladium catalysts. United States. doi:10.1021/j100142a018.
McCaulley, J A. Thu . "In-situ X-ray absorption spectroscopy studies of hydride and carbide formation in supported palladium catalysts". United States. doi:10.1021/j100142a018.
@article{osti_5651809,
title = {In-situ X-ray absorption spectroscopy studies of hydride and carbide formation in supported palladium catalysts},
author = {McCaulley, J A},
abstractNote = {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.},
doi = {10.1021/j100142a018},
journal = {Journal of Physical Chemistry; (United States)},
issn = {0022-3654},
number = ,
volume = 97:40,
place = {United States},
year = {1993},
month = {10}
}