Silicon microreactors for measurements of catalytic activity

The topic of this project is the design and fabrication of chemical microreactors with short response time and high sensitivity to low catalyst areas. The microreactors are intended as analytical tools in experiments concerning heterogeneous catalysis, photocatalysis, and electrocatalysis. The reactors consist of a microchannel system etched in an oxidized silicon chip and sealed with a glass lid using anodic bonding. The chip design relies on a gas flow through the channel system and is designed for reactions at pressures at the order of 1 bar. A high sensitivity is obtained by directing the entire gas flow through the reaction zone to a mass spectrometer, thus ensuring that nearly all reaction products are present in the analyzed gas flow. An experimental study has been carried out of the conditions for cavity collapse during anodic bonding of wide, shallow grooves etched in silicon. The aim of this study has been to determine appropriate dimensions for the reaction chamber in the microsystem. It has been found that 200μm diameter circular silicon pillars distributed in the chamber are effective in preventing cavity collapse in such grooves. In particular, the pillars allow anodic bonding without collapse of 3μm deep, 1 cm diameter circular reaction chambers. During the project, a microreactor has been developed for photocatalysis and heterogeneous catalysis in gas phase reactions. To demonstrate the operation of the microreactor, CO oxidation on low-area platinum thin film circles has been employed as a test reaction. Using temperature ramping, it has been found that platinum catalysts with areas as small as 15μm2 are conveniently characterized with the device. A setup for locally cooled anodic bonding of microreactors is presented. The aim with this setup is to avoid catalyst deactivation in the reactor during bonding. A finite element analysis has been carried out to investigate the temperature distribution during bonding in a microreactor. The analysis suggests that the setup can effectively keep the reaction chamber temperature below 50 ◦C while the rest of the chip bonds. This is in good agreement with direct temperature measurements. A two-phase mesh microreactor has been developed, in which a gas and a liquid phase can be brought into contact. The reactor is intended for characterization of photoelectrode materials in photoelectrolysis, and the gas-liquid-interface is stabilized by a highly perforated, hydrophobic silicon membrane. The device allows measurements of electrode current simultaneously with direct product detection. The operation of the device has been demonstrated employing electrolysis of water as a test reaction.