Experimental (XAS STEM TPR and XPS) and Theoretical (DFT) Characterization of Supported Rhenium Catalysts
A high surface area supported Re-based catalyst, fundamental to heterogeneous catalysis, is studied in the oxidic and reduced states using a combination of experimental (XAFS, STEM, TPR, and XPS) and theoretical (DFT and X-ray spectroscopy simulations) approaches. In the calcined dried catalyst, the Re species is present as an isolated trioxo(oxoaluminate) Re(VII) species. The temperature at which the Re undergoes reduction is a function of the hydrogen partial pressure and temperature ramp rate, but the maximum rate of reduction occurs in the range 300-400 C. Following reduction at 500 or 700 C in dry hydrogen, the Re is present as a mixture of species: unreduced trioxo(oxoaluminate) Re(VII) species, Re nanoclusters, and isolated Re atoms. By using a multifaceted approach, it is apparent that the majority species is an isolated Re adatom bound to the alumina support. DFT calculations identify several likely adsorption sites for these Re adatoms on the [110] surface of {gamma}-Al{sub 2}O{sub 3}. The final extended X-ray absorption fine structure (EXAFS) model taking into account these three species is used to identify the dominant adsorption site for Re on the alumina surface. FEFF8 X-ray absorption near-edge spectroscopy (XANES) calculations of unsupported and alumina-supported Re nanoclusters provide interpretation of the shape and edge position of the Re L{sub 3}-edge XANES after reduction. The presence of moisture during reduction stronly affects the mobility of the Re on the alumina leading to agglomeration. Subsequent air exposure of a reduced catalyst readily reoxidizes the reduced Re. The power of using a combination of analysis tools provides insight into the behavior of dispersed Re on supported alumina under oxidizing and reducing conditions relevant to heterogeneous catalysis.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- Sponsoring Organization:
- USDOE SC OFFICE OF SCIENCE (SC)
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 1042241
- Report Number(s):
- BNL-97919-2012-JA; TRN: US201212%%652
- Journal Information:
- Journal of Physical Chemistry C, Vol. 115, Issue 13; ISSN 1932-7447
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ABSORPTION SPECTROSCOPY
ADSORPTION
AGGLOMERATION
CATALYST SUPPORTS
CATALYSTS
FINE STRUCTURE
DENSITY FUNCTIONAL METHOD
HETEROGENEOUS CATALYSIS
HYDROGEN
MIXTURES
MOBILITY
MOISTURE
OXIDATION
PARTIAL PRESSURE
REDUCTION
RHENIUM
SHAPE
SPECTROSCOPY
SURFACE AREA
SURFACES
SIMULATION
TEMPERATURE DEPENDENCE
X-RAY PHOTOELECTRON SPECTROSCOPY
X-RAY SPECTROSCOPY