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Potassium-containing BEA zeolites were prepared by ion-exchange from NH4-BEA with potassium nitrate aqueous solution or ion-exchange combined with impregnation. The samples were used as basic catalysts for aldol condensation of furfural and acetone studied in a batch reactor at 100 °C, autogenous pressure and a reaction time of 2 h. To establish a relationship between physico-chemical properties and catalytic behavior of BEA zeolites, the samples were characterized by XRD, N2 adsorption, FTIR, calorimetry, and TGA. The ion-exchanged K-BEA catalysts exhibited low activity in the aldol condensation because of a weak strength of intrinsic basic sites. In contrast, the samples prepared by ion exchange combined with impregnation possessed strong basic sites, plausibly K2O clusters, and demonstrated appreciable activity in the aldol condensation. TGA results proved that, in contrast to acidic zeolites, basic sites of impregnated BEA samples hardly contribute to the formation of heavy carbonaceous deposits during the reaction what could be advantageous for the stable behavior of catalysts.