Collaborative Research Centre 546

"Structure, Dynamics and Reactivity of Aggregates of Transition Metal Oxides"

Project B1

General information
 
 

Title:

Structure-reactivity relations of vanadium oxide aggregates supported on ordered transition metal oxide surfaces

Research areas:

Chemical physics, surfaces, model catalysis

Leiter: Dr. Shamil Shaikhutdinov Fritz-Haber-Institut der Max-Planck-Gesellschaft Abteilung Chemische Physik Faradayweg 4-6 14195 Berlin-Dahlem Telefon: 030 8413 4114 Telefax: 030 8413 4105 E-Mail-Adresse: shaikhutdinov@fhi-berlin.mpg.de   Prof. Dr. Hans-Joachim Freund Fritz-Haber-Institut der Max-Planck-Gesellschaft Abteilung Chemische Physik Faradayweg 4-6 14195 Berlin-Dahlem Telefon: 030 8413 4100 (4102, 4104) Telefax: 030 8413 4101 E-Mail-Adresse: freund@fhi-berlin.mpg.de

Abstract:

During the previous period, we focused on the preparation and structural properties of vanadia nanoparticles deposited on thin oxide films such as alumina and silica. For these studies, we have employed a unique experimental setup combining LEED, STM, XPS, TPD and IRAS facilities in one UHV chamber. In particular, we showed that the vanadia/support interface might play an important role in the reactivity of the vanadia based catalysts. It has turned out however, that preparation of the well ordered silica films is extremely difficult and time-consuming, therefore, to date, the studies on adsorption properties of the vanadia particles were limited to CO as a probe molecule. In the forthcoming period, two main goals will be pursued: a) investigation of the reactivity of the supported vanadia particles towards catalytically relevant molecules such as methanol and propane; b) the studies on the origin of the support effects, reported in the literature, on the properties of vanadia particles. Adsorption behaviour of vanadia will be studied by infrared spectroscopy in combination with a temperature programmed desorption. We anticipate that the reactivity of the vanadia/alumina(silica) systems under the UHV conditions is low, therefore, the studies under the higher pressure conditions become necessary. Currently, we are building a high-pressure cell for performing IRAS studies at the mbar-pressure range. The cell will be also used for studying effects of high O₂ pressure on the surface structure of the vanadia particles. It is well documented that catalytic properties of vanadia strongly depend on the oxide support. For example, turnover numbers for vanadia catalysts in methanol oxidation are about two orders of magnitude higher when supported on zirconia, titania and niobia as compared to alumina and silica. In other words, the reducible oxide support dramatically changes the reactivity of vanadia particles in reactions involving oxygen. We are going to study these effects by comparing structure and reactivity of vanadia/alumina system with vanadia deposited on the reducible oxide films. It has been reported that well-ordered titania and ceria films can be grown, for example, on a Ru(0001) substrate.
The results on the supported vanadia particles will be compared to those obtained for the thick vanadia films studied in project C1 (H.-J. Freund, H. Kuhlenbeck). The intense collaboration with the project C5 (J. Sauer, V. Ganduglia-Pirovano) will continue?

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