Micro-Flow Reactors for Kinetic Studies of Model Catalysts made by Electron-Beam Lithography

Doktorsavhandling, 2000

The main objective of this work is to explore the potential of using electron beam lithography (EBL) to prepare well defined supported model catalysts, which can be used for catalytic research. The work has involved three major areas (i) EBL-fabrication of catalysts, (ii) design of a micro-flow reactor for catalytic evaluation, and (iii) problem oriented research using EBL-fabricated model catalysts. With the EBL technique supported model catalysts have been prepared consisting of arrays of Pt particles on SiO2 and CeOx. To evaluate the catalytic performance of the EBL fabricated model catalysts, a specially designed low-flow micro reactor has been constructed. The main feature is a very low flow through the reactor (approx. 1 microliter/second ) to match the small overall precious metal surface area presently attainable with the EBL technique (on the order of 1 mm2) for small particle sizes (<50 nm). The catalytic performance of the EBL fabricated model catalysts for CO oxidation was compared with other more established model systems, e.g., Pt-wires, and a good agreement is obtained. Promotional effects due to pre-reducing pre-treatments are shown for CO-oxidation on Pt/CeOx, while the opposite is shown for Pt/SiO2. Bistable reaction diagrams for CO oxidation on Pt/CeOx and Pt/SiO2 have been measured, and it is shown by mean-field simulations that an extra channel of oxygen supply to the Pt particles by surface diffusion on the ceria support, can explain the experimental findings. These results demonstrates a working concept for preparation and catalytic evaluation of EBL samples, well capable of functioning as model catalysts at operating conditions of scientific and practical interest.