Collaborative Research Centre 546

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

Project C1
 

General information
 
 

Title:

Electronic structure and adsorption mechanism of ordered surfaces of oxides of vanadium, molybdenum and niobium

Research areas:

Surface chemistry, adsorption, oxides

Leader:

Dr. Helmut Kuhlenbeck Fritz-Haber-Institut der Max-Planck-Gesellschaft Abteilung Chemische Physik Faradayweg 4-6 14195 Berlin-Dahlem Telefon: 030 8413 4222 Telefax: 030 8413 4307 E-Mail-Adresse:kuhlenbeck@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:

In the preceding periods the project C1 focused on the study of ordered oxide films and single crystals with respect to electronic properties, surface structure, and the interaction with adsorbates. Synchrotron radiation based methods (XPS, UPS, NEXAFS), thermal desorption spectroscopy, vibrational spectroscopy, LEED, and lately also STM were applied. In the past the investigations were restricted to vanadium oxide surface (V₂O₃(0001), VO₂(110) and V₂O₅(001)). The proposed studies are essentially complete but some finalizing investigations still need to be performed, especially for the case of the chemical activity of defective V₂O₅(001) surfaces. For the coming period we plan to extend the project in two directions. One direction is the investigation to molybdenum and niobium oxides. Similar to vanadium oxides these oxides also catalyze partial oxidation reactions. However, the catalytic activities may be significantly different. In laboratory experiments we could already prepare thin ordered MoO₂(100) films. In order to be able to prepare also higher oxides a high-pressure oxidation cell has been constructed. First results for ordered MoO₃ and V₂O₅ layers could already be obtained. In the case of niobium oxides detailed results do exist for thin films on Cu₃Au(100), partly obtained by the group of Horst Niehus (C2) and partly in the projects B1 (S. Shaikhutdinov) and C1 (this project). Another direction of extension of the project’s activities will be the investigation of catalytic processes at elevated pressures. Many reactions can not be studied very well under UHV conditions. Sum frequency generation (SFG), polarization modulated infrared spectroscopy (PM-IRAS) and gas chromatography are available in the department for in-situ studies at elevated pressure. These methods will be accessible for future studies in the framework of this project. Another, somewhat less advanced approach is the ex-situ study of reaction products which should be possible with the already mentioned high pressure cell. The reaction to be investigated first will be the oxidative dehydrogenation of propane which leads to the formation of propene.
In the past this project maintained a fruitful cooperation with theoretically oriented projects such as C6 (K. Hermann) and C5 (V. Ganduglia-Pirovano) which will be continued in the future. The cooperation with project B1 (S. Shaikhutdinov) is also important. This project investigates cluster/substrate systems and a comparison with results obtained in C1 for thin films may lead to additional insights.