A unique experimental setup developed in house is used to evaluate the performance of OCM catalysts under isothermal conditions. The unit can operate isothermally under various conditions with temperatures up to 950°C and total pressure up to 20 bar. The feed section has four independent gas feed lines (O₂, CH₄, N₂, He) with flow rates regulated by thermal mass flow controllers (MFCs, Bronkhorst). Sintered α-Al₂O₃ is used as the reactor material because of its thermal properties at elevated temperatures and its inertness for OCM. The reactor is 90 cm long, with external diameter of 12 mm, and an internal diameter of 8 mm. A thermowell, also made from α-Al₂O₃ (external diameter of 4 mm), is placed in the centre of the reactor. A thermocouple can move along the entire length of the reactor to measure of axial temperature profile. The reactor is placed inside a fluidized sand bath, which serves as oven with near isothermal conditions, even for a fast and highly exothermic reaction such as OCM. A GC system custom-built by Bruker provides online analysis of the products with simultaneous determination of O₂, N₂, CO, CO₂, CH₄, C₂, C₃ isomers and CH₂O in gaseous samples.