Raman spectra of La{sub 2}O{sub 3} dispersed on {gamma}-Al{sub 2}O{sub 3}
- Univ. Muenchen (Germany). Inst. fuer Physikalische Chemie
- Pennsylvania State Univ., University Park, PA (United States). Dept. of Chemical Engineering
Lanthanum oxide dispersed on alumina is a system of considerable interest for at least two reasons. First, it has been stated that La{sub 2}O{sub 3} is the best-known inhibitor of sintering in {gamma}- and other transition aluminas, thus it can have a role in automotive exhaust catalysts. Second, La{sub 2}O{sub 3} has been found to be a selective catalyst for the reduction of NO{sub x} to N{sub 2} with CH{sub 4} in excess O{sub 2}. Raman spectra have been obtained for La{sub 2}O{sub 3} dispersed on Al{sub 2}O{sub 3}, but only after La{sub 2}O{sub 3} coverages reach one theoretical monolayer or higher. Sharp peaks at 104, 191, and 408 cm{sup {minus}1} were observed, which are in excellent agreement with previous studies of bulk La{sub 2}O{sub 3}; however, two additional broader, but intense bands not previously reported were also observed at 322 and 935 cm{sup {minus}1}. These latter two bands disappear at temperatures of 450 K or higher, but they returned with full intensity upon cooling to 300 K. A sample of bulk La{sub 2}O{sub 3} (a-form) with a low surface/volume ratio also exhibited weak peaks at these latter two positions. Raman spectra taken with different exciting laser lines showed that the bands at 322 and 935 cm{sup {minus}1} can be attributed to a laser-excited luminescence. It is inferred that these luminescence bands are evidence for the presence of oxygen anion vacancies. After exposure to NO at 300 K, two peaks developed at 747 and 1047 cm{sup {minus}1} which can be assigned to a surface nitrate species.
- OSTI ID:
- 659094
- Journal Information:
- Journal of Catalysis, Vol. 178, Issue 2; Other Information: PBD: 10 Sep 1998
- Country of Publication:
- United States
- Language:
- English
Similar Records
Structure and Vibrational Properties of Potassium-Promoted Tungsten Oxide Catalyst Monomeric Sites Supported on Alumina (K2O/WO3/Al2O3) Characterized Using Periodic Density Functional Theory
Crystal-field-excitation--phonon coupling in Pb[sub 2]Sr[sub 2]NdCu[sub 3]O[sub 8+[delta]]