Single-atom catalysts (SAC) are much-studied in surface science due to their great potential in heterogeneous catalysis. Model systems consisting of metal adatoms on single-crystal metal-oxide surfaces are being investigated in ultra-high vacuum (UHV) to understand the fundamentals of SAC. A step towards industrial SAC systems is an examination of idealized model systems under more realistic conditions, i.e., at elevated pressures and temperatures. This work aims to develop a UHV-compatible reaction cell, enabling sample exposure to gases at about 1 mbar pressure and temperatures up to 300°C. The composition of the exhaust gas from the reactor is quantitatively analyzed by mass spectrometry. Due to the low number of active sites on model SAC, measuring turnover frequencies presents a significant challenge. Therefore, we are investigating methods to optimize detection techniques.