In this study, water vapor adsorption properties of the clinoptilolite rich zeolite tuff, from Bigadic (Turkey), and its modified forms were examined. The modified forms were obtained by treating the tuff with HCl solutions (0.032, 0.16, 0.32, 1.6 or 5 M) at 25, 40, 75 and 100°C for 3 h. Infrared spectroscopy and water vapor adsorption were used for the characterization of the zeolites. Langmuir, BET and Dubinin-Raduschevich methods were applied in the analysis of water vapor adsorption data. Applications of Dubinin Raduschevich equation to the water adsorption data displayed that the super-micropore volume was not very sensitive to acid treatment. It was found out that the Langmuir surface area and ultra-micropore volume depend on the degree of the removal of aluminum from the structure.

Abstract. CO 2 and N 2 adsorption on the acid treated natural and synthetic zeolites at 5 • C and 25 • C was studied. The system heterogeneity was higher for CO 2 than N 2 adsorption and decreased with acid treatment.

In this study, isomerization of a-pinene was studied over several acid-treated natural zeolite catalysts rich in clinoptilolite. Zeolite samples were contacted with HCl at different concentrations at 30 C or at 60 C for 3 and 24 hours and tested in isomerization reaction of alpha-pinene. The catalysts prepared were characterized by XRD, nitrogen adsorption, and acidity studies. Acidity strength and the distribution of Lewis and Brö nsted acid sites of the catalysts were determined, and their catalytic activities in a-pinene isomerization and selectivities to main reaction products, camphene and limonene, were investigated. Acid treatment improved the selectivity of catalyst samples to camphene, decreasing the selectivity to limonene, probably forcing limonene to secondary reactions at high conversions.The kinetics of a-pinene consumption was described by first-order kinetics. Two kinetic models were tested for the reaction mechanism and one model was found to give a good correlation between the theoretical and experimental data. In the models, the key intermediate was the pinylcarbonium ion, which was formed irreversibly from a-pinene.Number and distribution of Lewis and Brö nsted acid sites affect the formation of bicyclic and monocyclic products.

a b s t r a c tIn this study, we focused on the effect of ultrasound on ion exchange kinetics to obtain the Li-, Ca-and Cerich NaX zeolite. The results were compared to those obtained from the traditional batch exchange method under similar conditions. Contact time and initial cation concentration (fold equivalent excess) were studied. Ultrasound enhanced the replacement of Na + ion with Li + , Ca 2+ and Ce 3+ ions in the extra-framework of zeolite up to 76%, 72% and 66%, respectively. The intraparticle diffusion is the rate limiting step in the ion exchange for both exchange methods. As compared to the traditional exchange method, the ultrasonic method applied in this study was found to be very effective on the exchange amount at equilibrium.

The carbon dioxide and water vapour adsorption properties of local clinoptilolite-rich material, both as the original and as lead-, barium- and hydrogen-rich forms, were examined. The lead- and barium-rich forms were prepared by treatment of the original clinoptilolite with Pb(NO3)2 and BaCl2 respectively, while the hydrogen-rich form was prepared by NH4Cl and heat treatment. Water and CO2 adsorption experiments were conducted in a volumetric system under static conditions, with low-pressure adsorption data being used for the characterization of the natural, Pb-rich, Ba-rich and H-rich clinoptilolite samples. Although the existence of barium-exchange was not noted, an appreciable decrease in CO2 adsorption was observed with the Pb-rich and H-rich forms due to a decrease in the electrostatic interaction between the surface and the adsorbate. Application of the Dubinin–Astakhov equation to the water adsorption data established the existence of micropores of different sizes that exhibited different adsorption mechanisms.

a b s t r a c tAqueous interactions of natural zeolitic material in as-received and modified forms were studied. The zeolitic materials was interacted with acidic (hydrochloric acid, lactic acid, acetic acid) and basic (sodium hydroxide) solutions. Ion exchange, adsorption, complex formation, precipitation and cation hydrolysis were possible interaction mechanisms affected by the amount and cation content of zeolite and pH. The dominant mechanisms seemed to be ion exchange and adsorption in HCl solution when zeolite was used in the as-received form, but dissociation of outer-sphere complexes when modified zeolite was used. In lactic acid, acetic acid as well as the basic solution, cation hydrolysis and complex formation were additional mechanism in the interactions.

Synthetic zeolites have shown great potential for a number of applications in various fields such as adsorption, separation and ion exchange. They have unique structural properties such as uniform pores, high surface area, high ion exchange capacity and high thermal stability [1]. Synthetic NaX zeolite is composed of eight sodalite cages joined through six-membered oxygen rings in a tetrahedral arrangement. It has also supercage accessible through twelve-membered oxygen rings as seen in Fig. 1 [2]. The negative charges of the AlO 4 units which built the framework are balanced by exchangeable cations. These cations depending heavily on the size, charge density and distribution of cations in the porous structure play a very important role in adsorption, dehydration and ion exchange properties. The water and other adsorbate molecules are loosely bound to these cations. The cations can be introduced into the supercages to affect acid-base properties of zeolite. CO 2 is a small, non-polar, weak acidic molecule and can be adsorbed on the surfaces having basic character. The basic properties can be increased with the aluminum content of the zeolite structure with decreasing cation electronegativity. Besides to the properties mentioned above, the quantitative structural properties of NaX zeolite based on thermal analysis (thermogravimetric analysis (TG), differential scanning calorimetry (DSC)) data are employed to gain quantitative information about the coordinated water in channels and cages of the zeolite [3]. Based on dehydration of zeolites, water is classified as loosely bound water, zeolitic water and crystal water [4]. The cations located in the cavities and the channel walls are coordinated with water molecules which give rise to dehydration behavior of zeolites. Dehydration behavior of NaX zeolite depends on the amount and type of exchangeable cation, the Al/Si ratio, the presence or absence of H 2 O, time and temperature [5]. Dehydration enthalpy change and thermal stability can be determined by using thermoanalytical techniques [6].The objective of this work is to determine the effect of cation (Li + , K + , Ca 2+ and Ce 3+ ) on the CO 2 adsorption and the dehydration behavior of the NaX zeolite. Analysis and Calorimetry, Vol. 94 (2008) It was observed that both dehydration and CO 2 adsorption properties are related to cation introduced into zeolite structure.

Abstract:In this study the effect of ultrasound of the cerium exchange was studied. The results were compared to those obtained from traditional batch exchange method. Contact time, initial cation concentration (fold equivalent excess) and the types of the ultrasound were studied. Ultrasonic probe, which is the most effective method, enhanced the replacement of Na + ion with Ce 3+ ion in the extra-framework of zeolite up to 73 % by applying 5 consecutive ion exchanges. The cerium in the solution caused to be formed cerium oxides on the crystal surface occluding the pores. Thus the specific surface area of cerium exchanged zeolite was decreased due to formation of cerium complexes on the surface and into the pores.