As for possible ideas for the actual experimental setup, I found that in the study below the authors use a [presumably automated] syringe pump and a capillary tube to inject water+ethylbenzene inside a tubular reactor not exceedingly different in principle than what I had in mind. Gases like N2, H2, CO2 are fed through different conduits. They report that the liquids get immediately vaporized upon entering the chamber (at 600 °C) and prior getting in contact with the catalyst sample. The main differences here from what I wanted to achieve are that the reactants flow over the catalyst sample (here in milligram-amounts) rather than being forced to diffuse through it, and heater location/arrangement. Also, the catalysts are synthesized ex-situ.
Li Z, Shanks BH. Stability and phase transitions of potassium-promoted iron oxide in various gas phase environments. Applied Catalysis A: General. 2009 Feb 15;354(1-2):50-6. https://doi.org/10.1016/j.apcata.2008.11.007