A study has been made of coke combustion for regenerating a HZSM-5 catalyst deactivated in the transformation of aqueous ethanol into hydrocarbons (BTG process). Combustion activation energy decreases with the H/C ratio of the coke and this ratio decreases with aging prior to combustion. Consequently, the prior aging of the coke is required in order to reproduce the combustion kinetics (activation energy approximate to 29.50 kcal/mol). By conducting experimentation following reaction-regeneration cycles, activity recovery has been studied by following the composition of the products obtained in the reaction cycle subsequent to each partial regeneration of the catalyst. The acidity of the partially regenerated catalysts has been determined by differential adsorption and TPD of ammonia. It has been proven that a catalyst subjected to severe deactivation during the reaction and regeneration steps undergoes a slight hysteresis in the activity-coke relationship, whereas there is no hysteresis in the acidity-coke relationship, except in the first cycle of reaction-regeneration in which there is a slight irreversible loss of acidity with no bearing on the kinetic results. (c) 2005 Elsevier B.V. All rights reserved.