Characterization of Pd/c-Al2O3 Catalysts Prepared Using [Pd(hfac)2] in Liquid CO2
A series of Pd/{gamma}-Al{sub 2}O{sub 3} catalysts was prepared from (Pd(hfac){sub 2}) (hfac = hexafluoroacetylacetonate) in liquid carbon dioxide using the method reported by Kim et al. (Chem Mater 18:4710 (2006)). The catalysts were characterized using CO pulse chemisorption, diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray absorption fine structure (XAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron microscopy. The catalysts were reduced initially in the high-pressure CO{sub 2} reaction cell using H{sub 2} at 75 C. Samples were removed, stored in a desiccator, and re-reduced in situ at 250 C prior to pulse chemisorption, DRIFTS and XAFS. CO pulse chemisorption evidenced that the Pd dispersion decreased from 55% to 5% as the Pd loading increased from 0.58 to 3.94 wt.%. The as-prepared 0.58 and 1.77 wt.% Pd/{gamma}-Al{sub 2}O{sub 3} catalysts (after air exposure) contained oxidized Pd species that were converted after in situ reduction to supported Pd particles. The average Pd particle sizes of these two catalysts (16 and 23 {angstrom}, respectively) estimated from the first-shell Pd-Pd coordination numbers are in good agreement with the CO chemisorption results. DRIFTS evidenced a prevalence of weakly bound linear CO (CO = 2083 cm{sup -1}) adsorbed on the 0.58 wt.% Pd catalyst. A 2.95 wt% Pd catalyst (49 {angstrom} average particle size) also exhibited a strong linear CO band (CO = 2093 cm{sup -1}). In contrast, CO chemisorption on a commercial 1 wt.% Pd/Al{sub 2}O{sub 3} catalyst (37 {angstrom} average particle size) gave predominantly 2-fold bridging CO species. We infer that the supported Pd particles prepared from (Pd(hfac){sub 2}) are rougher on the atomic scale (with a higher percentage of edge and corner atoms) than equivalently sized particles in conventionally prepared Pd/{gamma}-Al{sub 2}O{sub 3} catalysts.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 980056
- Report Number(s):
- BNL-92974-2010-JA; TRN: US201015%%1441
- Journal Information:
- Topics in Catalysis, Vol. 49, Issue 3-4
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ABSORPTION
AIR
ATOMS
CARBON DIOXIDE
CATALYSTS
CHEMISORPTION
COORDINATION NUMBER
DISPERSIONS
ELECTRON MICROSCOPY
FINE STRUCTURE
LIQUIDS
LOADING
PARTICLE SIZE
PARTICLES
PRESSURE RANGE MEGA PA 10-100
PULSES
REDUCTION
SPECTROSCOPY
X-RAY PHOTOELECTRON SPECTROSCOPY
national synchrotron light source