Characterization of potassium-modified FAU zeolites and their performance in aldol condensation of furfural and acetone

Abstract The effects of both Si/Al ratio and preparation method (ion exchange vs. impregnation) on the physico-chemical properties of potassium modified Y zeolites were studied in detail. The samples were used as basic catalysts for aldol condensation of furfural and acetone. A relationship between physico-chemical properties and catalytic performance of potassium-containing Y zeolites was established using XRD, N 2 physisorption, IR spectroscopy of adsorbed CO 2 ‎ and CO 2 -TPD. Neither ion-exchange nor impregnation with KNO 3 removed completely all acid sites in Y (Si/Al = 2.5). Moreover, K 2 O clusters were not formed under thermal activation of the samples prepared from the parent H-Y(2.5). As a consequence, both ion-exchanged and impregnated K-Y(2.5) possessed low activity in aldol condensation, but they had high ability to dehydrate reaction products. In contrast, thermal activation of USY zeolites (Si/Al = 15 and 40) impregnated with potassium resulted in the formation of K 2 O species which, according to CO 2 -IR spectroscopy and CO 2 -TPD, were strong basic sites. It was concluded that the lower amount of proton sites available for an ion-exchange together with the ‎larger mesopore volume and more defective crystalline framework promoted the accumulation of KNO 3 in the USY zeolites during the impregnation step. Subsequently, K 2 O species were formed by thermal treatment. Impregnated and calcined USY zeolites possessed a superior catalytic activity in comparison with HY (Si/Al = 2.5). The presence of K 2 O species as strong basic sites in K-impregnated USY zeolites was favorable for both the high activity of the catalysts in aldol condensation and the occurrence of the second condensation step.