Enabling real-time detection of photocatalytic reactions by a re-useable micro-reactor

We present a highly sensitive and versatile Si-based mu-reactor for photocatalytic experiments. The mu-reactor can be operated in front side (through a borosilicate window) as well as backside (through the catalyst support) illumination. The mu-reactor is sealed by compressing the Si-based microchip, a parafilm gasket and the supported catalyst by four screws. This design allows for fast and reliable assembly of the mu-reactor and the microchip is re-usable for several independent experiments, making the presented mu-reactor ideal for catalyst screening studies. We analyze volatile reactants on-line by connecting the mu-reactor to a mass-spectrometer. The limiting capillary of the mu-reactor allows for nearly 100% collection efficiency (i.e. every produced molecule will be collected) by limiting the gas flow to the mass-spectrometer-enabling highly sensitive measurements and an absolute calibration. Finally, the small height of the reactor volume results in very fast response times, which make the reactor suitable for studies of transient activity phenomena-including catalyst activation and deactivation. We demonstrate these capabilities of the mu-reactor by performing CO oxidation experiments on a TiO2 thin film with subsequent calibration of the chip. Based on a mathematical model of the mu-reactor we additionally present a method for determining the residence time, the reaction volume and the working distance.