Ultra-high vacuum compatible reactor for model catalyst study of ammonia synthesis at ambient pressure.

A high sensitivity reactor was developed to study slow reactions, such as ammonia synthesis over low surface area model catalysts at 1 bar and up to 550 °C. The reactor is connected to an ultra-high vacuum system with a transferable sample design, which allows for cleaning, preparation, and spectroscopic characterization of samples before and after the reaction without exposure to any contaminated environment, such as air. A quasi-closed small volume (250 µl) quartz glass reaction cell is integrated through a capillary with a quartz glass sniffer tube connected to a mass spectrometer. The capillary reduces the 1 bar pressure in the cell to 10-7 mbar in the sniffer tube and mass spectrometer chamber. A quartz fiber-guided laser is used to heat up the sample, and the temperature can be regulated by the proportional-integral-derivative controlled laser power output for fast reaction kinetics research. Proof of principle ammonia synthesis experiments in this reactor at 1 bar, 350-500 °C on Fe(111) single crystal and mass-selected Ru clusters supported on CeO2 thin film yield kinetic parameters that agree very well to those reported in the literature.