The role of acid centers of natural zeolites in synthesis of ethyl-tert-butyl ether (ETBE) was investigated. The method for calculation of desorption energy distribution from stepwise desorption experiment was proposed. The method allows to calculate continuous desorption energy distribution of surface sites using different probes (ammonia, ethanol, iso-butylene, etc.). The correlation between rate of ETBE synthesis and concentration of weak acid sites (E-NH3 = 70-75 kJ mol(-1)) was found. It has been shown that during ETBE synthesis iso-butylene is activated mainly on medium and strong acid centers and forms one type of surface complex, while ethanol forms two types of adsorbed complexes. Low energy surface ethanol complexes (E = 53-60 kJ mol(-1)) located on weak acid centers of zeolites were found to be active in ETBE synthesis. These complexes govern the catalytic activity of catalyst in ETBE synthesis. (c) 2006 Elsevier B.V. All rights reserved.