A transmission infrared microreactor cell which holds a pressed disc in a controlled atmosphere and allows microwave and conventional heating up to 423 K is demonstrated using the oxidation of carbon monoxide over the standard catalyst EUROPT-1. Optical characteristics are determined by the choice of CaF2 as the window material, allowing transmission from 77 000–1000 cm−1. An oscillating microwave power regime with a peak height of 200 W is used and time-resolved infrared spectra and mass spectrometry show oscillations in the reaction which correspond to the microwave heating.