Structure of Rh/TiO/sub 2/ in the normal and the SMSI state as determined by extended x-ray absorption fine structure and high-resolution transmission electron microscopy

Journal Article · Thu Apr 07 04:00:00 EDT 1988 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100318a041· OSTI ID:5129757

Martens, J H.A.; Prins, R; Zandbergen, H; Koningsberger, D C

Extended X-ray absorption fine structure (EXAFS) and high-resolution transmission electron microscopy (HRTEM) have been used to study the structure of a RhTiO/sub 2/ catalyst. After reduction in H/sub 2/ at 473 K (when the catalyst is in the normal state) the metal particles contain on the average five rhodium atoms and are situated preferably on edges of the TiO/sub 2/ crystallites but also on (101) and to a lesser extent on (001) anatase crystal faces. Reduction in H/sub 2/ at 723 K leads to the SMSI state. Besides oxygen neighbors from the support, the rhodium metal atoms, in the metal-support interface have Ti/sup n+/ neighbors at 3.4 and 4.3 A. These distances and their coordination numbers fit well with a model in which the metal particles rest on a TiO/sub 2/ suboxide. This indicates that the supporting oxide near the metal particle has been reduced to a suboxide of TiO/sub 2/. In the SMSI state no indication for coverage has been found with either EXAFS or HRTEM. On the contrary, exposing the catalyst in the SMSI state to oxygen at 100 K resulted in changes in the EXAFS spectrum due to physisorption of oxygen. Consequently, in the SMSI state the particles are either not covered or are incompletely covered with TiO/sub x/. Since a RhAl/sub 2/O/sub 3/ catalyst under the same conditions became partly oxidized, it is evident that for the RhTiO/sub 2/ catalyst oxidation has been suppressed. This is most probably the result of an electronic influence from the reduced supporting oxide. Even after oxygen admission at room temperature, the rhodium particles on the TiO/sub x/ support remain in the metallic state. The TiO/sub x/ suboxide in the vicinity of the metal particles starts to reoxidize and the metal-support interaction becomes weaker.

• Research Organization: Eindhoven Univ. of Technology (Netherlands)
• OSTI ID: 5129757
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 92:7; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ABSORPTION SPECTROSCOPY
CATALYSIS
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
DATA
ELECTROMAGNETIC RADIATION
ELECTRON MICROSCOPY
ELEMENTS
EXPERIMENTAL DATA
FINE STRUCTURE
INFORMATION
IONIZING RADIATIONS
METALS
MICROSCOPY
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
RADIATIONS
RHODIUM
SPECTROSCOPY
STRUCTURAL CHEMICAL ANALYSIS
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
TRANSMISSION ELECTRON MICROSCOPY
X RADIATION