 Operando spectroscopy requires measurement of the catalyst under (ideally) real "working conditions", involving comparable temperature and pressure environments to those of industrially catalyzed reactions, but with a spectroscopic device inserted into the reaction vessel.The parameters of the reaction are then measured continuously during the reaction using the appropriate instrumentation, i.e., online mass spectrometry, gas chromatography or IR/NMR spectroscopy.Operando instruments "(in situ cells)" must ideally allow for spectroscopic measurement under optimal reaction conditions.