It is firstly discovered that ZnCl2 modified gamma-Al2O3 solid Lewis acidic catalysts (ZnCl2/,gamma-Al2O3), which are prepared by solid-state reaction, are very active and extremely selective for the preparation of guaiacol by the vapor phase O-methylation of catechol with methanol in a fixed-bed reactor at 553 K, under the optimum reaction conditions, the conversion of catechol and the selectivity for guaiacol are up to 81.8 and 90.9%, respectively over ZnCl2 (10%)/gamma-Al2O3 and by far better than the reaction results over the solid Bronsted acid catalyst (HY), proposing that the weak coordination of catechol with the Zn2+ sites of ZnCl,/gamma-Al2O3 plays a key impact on the high selectivity for guaiacol. The recycling tests indicate that the modification of ZnCl2 could significantly improve the catalytic stability of gamma-Al2O3 by it efficiently restraining the catalyst's coking. And the deactivation of ZnCl2/gamma-Al2O3 is mainly caused by its ZnCl2 leaching and surface coking in the run procedure, therefore its catalytic activity can be only partly recovered by the calcination in air at 773 K for 4 h. (c) 2005 Elsevier B.V. All rights reserved.