Surface defects on metal oxide nanoparticles

Research project P 14731 Surface defects on metal oxide nanoparticles Erich KNÖZINGER 09.10.2000 The huge abundance of methane (CH4) which is relatively easily accessible in the earth`s crust have so far been exploited nearly exclusively as an energy source. The application as an educt for the production of more valuable chemicals such as C2 hydrocarbons essentially suffered form the fact that the respecitive technological procedures (oxidative coopling of mehtane, OCM) have so far not met with economical requirements. As a matter of fact the activity and selecivity data provided by the heterogeneous catalysts (pure and mixed metal oxides) applied in the past have not been satisfactory. In the course of previous projects the applicant`s group has produced pure and surface doped MgO nanoparticles with the following outstanding properties: - thermal stability in the OCM relevant temperatrue range (650-850C) - dramatically increased (one order of magnitude) surface concentrations of low coordinated sites and vacancies. - variablility in the chemical surface properties such as basicity. Parallel to these preparative activities a successful strategy of characterizing all types of reactive surface defects by UV/VIS, IR and EPR spectroscopy has been developed. In the present project a systematic study of the interactions between the OCM educts (CH4, O2) and the surface defects on the oxide nanoparticles by the above mentioned spectroscopic techniques is intended. The results will then be correlated to activity and selectivity data. Two aspects which are intimately related to our detailed knowledge of the possibily OCM relevant surface centres, play a crucial role in the research work. On one hand the diverse types of surface centres will be subjected to systematic physical (wavelength selective UV induced processes) and/or chemical modifications, in order to study later on the catalytic consequences. On the other hand the inclusion of UV excitation in the heretogeneously catalysed process should reduce the required reaction temperature. - As a major issue of this project a relevant contribution to the understanding of the Ocm reaction mechanism is expiected which should then help to improve the catalyst`s activity and selecivity.