The successive steps occurring during conversion of methylbutynol (MBOH) on a basic NaX zeolite catalyst were characterized by combined micro-GC and operando DRIFT spectroscopy, assocd. to TPD-MS expts. These techniques permit to reveal a very strong and fast initial decrease in MBOH consumption, assocd. to some water desorption and to a deficit in acetone that is a product formed together with acetylene, in agreement with the basic route. The origin of deactivation, the nature and reactivity of the adsorbed compds. and their relative strengths of adsorption are discussed on the basis of the evolution of the operando DRIFT spectra with time on stream and next upon keeping the used catalyst in static then under flowing N2. The FTIR signatures of the three different modes of MBOH adsorption are detd. and only the mode involving a zeolite acid-base pair is found reactive. Aldolic condensation is identified but solely to a minor extent in flowing conditions of the reaction whereas it is significantly enhanced in static. Thus, the apparent initial deactivation can be ascribed mainly to MBOH adsorption. [on SciFinder(R)]