X-ray Absorption Spectroscopic Investigatin of Partially Reduced Cobalt Species in Co-MCM-41 Catalysts During Synthesis of Single-Wall Carbon Nanotubes
Chemometric tools were employed to analyze the in-situ dynamic X-ray absorption spectroscopy data to probe the state of Co-MCM-41 catalysts during reduction in pure hydrogen and under single-wall carbon nanotube synthesis reaction conditions. The use of the progressive correlation analysis established the sequence in which changes in the spectral features near the Co K edge occurred, and the evolving factor analysis provided evidence for the formation of an intermediate Co{sup 1+} ionic species during reduction of the Co-MCM-41 catalyst in pure hydrogen up to 720 C. This intermediate species preserves the tetrahedral environment in the silica framework and is resistant to complete reduction to the metal in H{sub 2}. While the Co{sup 2+} species is resistant to reduction in pure CO, the intermediate Co{sup 1+} species is more reactive in CO most likely forming cobalt carbonyl-like compounds with high mobility in the MCM-41. These mobile species are the precursors of the metallic clusters growing carbon nanotubes. Controlling the rates of each step of this two-stage reduction process is key to controlling the size of the metallic Co clusters formed in Co-MCM-41 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:
- 913849
- Report Number(s):
- BNL-78417-2007-JA; JPCBFK; TRN: US200804%%239
- Journal Information:
- J. Phys. Chem. B, Vol. 109; ISSN 1089-5647
- Country of Publication:
- United States
- Language:
- English
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