The influence of the acid/base properties of Mg2+-modified alumina on the steady-state and transient behavior of the EtOH to ethene dehydration was investigated by simultaneous gas phase and in-situ surface anal. The steady-state EtOH conversion and the ethene selectivity decreased with increasing catalyst basicity (Mg concn.). The ethene transient behavior is characterized by a stop-effect phenomenon, which is a drastic increase in reaction rate measured for a step-wise decrease in EtOH inlet concn. The relative augmentation of the ethene concn. under dynamic conditions is maximal for the catalyst with Mg/Al at. ratio 2.5. Compared to stationary expts., transients are much more sensitive to modifications of the catalyst acid/base properties. The expts. were described by a model considering the existence of acid and basic sites on the catalyst surface. The Mg concn. influences the kinetic parameters, whereas the site concns. do not show any significant variation. [on SciFinder (R)]