Morphological and Structural Changes during the Reduction and Reoxidation of CuO/CeO2 and Ce1-xCuxO2 Nanocatalysts: In Situ Studies with Environmental TEM XRD and XAS
We have studied the structural, morphological, and electronic properties of CuO/CeO{sub 2} and Ce{sub 1-x}Cu{sub x}O{sub 2} nanocatalysts during reduction/oxidation cycles using H2 and O2 as chemical probes. Time-resolved in situ characterization was performed by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) as well as aberration-corrected environmental transmission electron microscopy (ETEM). We have found that both types of nanocatalysts reduce to a Cu/CeO{sub 2} biphase system with significant oxygen vacancies in CeO{sub 2}. Important variations are seen in the Cu particle size and metal dispersion depending on the initial state of the copper oxide-ceria systems. During subsequent in situ oxygen annealing, the Cu precipitated from the CuO/CeO{sub 2} system reoxidized to form CuO through a Cu2O intermediate phase as expected. However, the Cu precipitated from the Ce{sub 0.8}Cu{sub 0.2}O{sub 2} solid solution behaved rather differently under oxidizing conditions, and neither oxidized to form CuO nor fully returned to a bulk Ce{sub 0.8}Cu{sub 0.2}O{sub 2} phase in solid solution. We found that 50% of the Cu returned to a Ce{sub 1-x}Cu{sub x}O{sub 2} solid solution, while the remainder was observed by in situ ETEM to form an amorphous copper oxide phase with a Cu oxidation state similar to Ce{sub 1-x}Cu{sub x}O{sub 2}, but with a local bonding environment similar to CuO. The behavior of the reduced Ce{sub 0.8}Cu{sub 0.2}O{sub 2} reflects strong interactions between Cu and the ceria matrix and illustrates the advantages of working with solid solutions of mixed oxides.
- 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:
- 1042215
- Report Number(s):
- BNL-97893-2012-JA; TRN: US1202757
- Journal Information:
- Journal of Physical Chemistry C, Vol. 115, Issue 28; ISSN 1932-7447
- Country of Publication:
- United States
- Language:
- English
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