Calorimetric and IR-Spectroscopic Study of Methanol Adsorption on Zeolites

• Published in: Journal of colloid and interface science 1994-07, Vol.165 (2), p.318-324
• Main Authors: Izmailova, S.G., Karetina, I.V., Khvoshchev, S.S., Shubaeva, M.A.
• Format: Article
• Language: English
• Subjects: 10 SYNTHETIC FUELS; 100300 - Synthetic Fuels- Properties & Composition- (1990-); 400201 - Chemical & Physicochemical Properties; ABSORPTION SPECTROSCOPY; ADSORPTION; ADSORPTION HEAT; ALCOHOLS; CALORIMETRY; CATALYSTS; ELECTROMAGNETIC RADIATION; ENTHALPY; HYDROXY COMPOUNDS; INFRARED RADIATION; INORGANIC ION EXCHANGERS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ION EXCHANGE MATERIALS; MATERIALS; METHANOL; MINERALS; ORGANIC COMPOUNDS; PHYSICAL PROPERTIES; RADIATIONS; SILICATE MINERALS; SORPTION; SORPTIVE PROPERTIES; SPECTROSCOPY; SURFACE PROPERTIES; THERMODYNAMIC PROPERTIES; ZEOLITES
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1006/jcis.1994.1235

The heats of CH 3OH adsorption on sodium faujasites and mordenites with different Si/Al ratios in the framework and on zeolites A, ZK-4, and ZK-5 were measured calorimetrically. The IR spectra of adsorbed CH 3OH were determined for the same zeolites. The decrease of cation concentration with increasing Si/Al ratio in the framework of faujasites, mordenites, and zeolites A and ZK-4 results in the decrease of CH 3OH adsorption heats for the broad coverage range and in weakening of the v OH disturbance for adsorbed CH 3OH. For highly dealuminated faujasite, the OH vibrations in adsorbed CH 3OH are strongly perturbed due to intermolecular interactions even at small coverages. The adsorption heat is very low in this case. Sodium cations at 8-membered oxygen rings of zeolite ZK-5 are more tightly bonded to the framework and so they are less active adsorption centers for CH 3OH molecules as compared to the appropriate cations of zeolite Na-A. The step on the adsorption heat curve for CH 3OH on zeolite Na-A in the coverage interval from 3 to 5 molecules/unit cell corresponds to the transition of adsorbed molecules from the interactions with cations in 8-membered oxygen rings to those with cations in 6-rings. The second step at coverages about 6 molecules/unit cell results from the crystallographic nonidentity of adsorption complexes formed by CH 3OH molecules with cations at 4-rings for different uptakes. The acidic structural OH groups of decationated mordenite are involved in strong hydrogen bonds with adsorbed CH 3OH molecules or protonate them.