Acid properties of NaKH-ferrierites of various exchange degrees studied by IR spectroscopy Original Research Articlev

The H/Na,K exchange was studied as one of the methods of modification of the acid properties of ferrierite. The concentration of Brönsted acid sites was determined, their acid strength and heterogeneity were followed by quantitative IR studies of ammonia desorption. The information on the Si status was obtained in MAS NMR experiments. IR studies showed that, even at low exchange degrees, hydroxyl groups both in 10-ring channels and in ferrierite cages were formed. In all the NaKH-ferrierites studied the concentration of Brönsted sites determined in our IR studies was practically identical as the concentration calculated from the zeolite composition. The acid strength of OH groups was found to increase with the H/Na,K exchange degree. The IR experiments of ammonia desorption evidenced that SiOHAl groups in our H-ferrierite were heterogeneous and several kinds of OH groups of various acid strength were found. It is possible that an increase of the acid strength with the exchange degree, i.e. with the amount of protons introduced is realized by the formation of less acidic hydroxyl groups at lower exchange degree, and more acidic hydroxyl groups at higher exchange degrees.