Sorptive Property Dependence of Catalytic Performance in -Xylene Isomerization over H/Ga-ZSM-5

The sorptive properties of a synthetic zeolite of type MFI with different concentration and nature of framework cations were studied using different probe molecules. The influence of the framework composition on the BET surface area and micropore void volume was examined using low-temperature nitrogen sorption. Sorption uptake kinetics using different probe molecules such as water, n-hexane, cyclohexane, o-, m- and p -isomers of xylenes, n-butylamine and tributylamine were also studied. The catalytic performance of different MFI isomorphs was studied in the o -xylene isomerization reaction. The probable correlation between the sorptive and catalytic properties has been discussed as a function of framework composition, acidity, o -xylene feed rate calculated in terms of mol/min g of catalyst and reaction temperature. The trend in the para selectivity was found to be proportional to the relative sorption of xylenes. In comparison to H/Al-ZSM-5, H/Ga-ZSM-5 with an almost identical framework composition exhibited lower para -selectivity. Even though all these zeolite catalysts possess identical frameworks consisting of 10-MR openings and intersecting channels, differences in the nature and concentration of the trivalent framework cations, the crystallite size and total acidity lead to changes in their sorptive properties and catalytic performance

Influence of Framework Silica to Alumina Ratio on the Sorption Characteristics of Synthetic Large-Port Mordenites

Synthetic large-port mordenite samples with different framework SiO 2 /Al 2 O 3 ratios (ranging from 10 to 35) obtained by direct hydrothermal crystallization were studied using different probe molecules. The influence of the framework aluminium content on the BET surface area and the micropore void volume in large-port mordenites was examined using low-temperature nitrogen sorption. Sorption uptake using different probe molecules such as water, benzene, n-hexane and cyclohexane was measured on the protonic form of the mordenite samples. The sorption energetics in large-port mordenites as a function of framework SiO 2 /Al 2 O 3 ratio was discussed on the basis of the isotherms for water sorption over the temperature range 303–403 K. The sorption data were analyzed in terms of different models of sorption isotherm equations. The wide variation in the isosteric heats of sorption of polar but amphoteric water molecules exhibited by mordenite samples with different framework Si/Al ratios demonstrate the heterogeneous character of the surface

Estimation by a Sorption Technique of the Amorphous Contribution in the Phases Obtained during the Hydrothermal Crystallization of LTL-Type Zeolite

Sorption techniques have been employed to estimate the amorphous contribution obtained during the progressive hydrothermal crystallization of the LTL phase from the K 2 O–Al 2 O 3 –SiO 2 –H 2 O system at 423 K. The curve showing the progressive depletion of the amorphous content as a function of the crystallization time exhibited an inverted sigmoidal-type shape indicative of distinct induction and crystallization stages. Samples with varying amorphous contributions were characterized by sorption uptake, XRD and chemical composition. The sorption uptake changes observed were found to be helpful in estimating the progress of the crystallization process. The influence of the amorphous contribution on the BET and Langmuir surface areas, and on the micropore void volume was examined using low-temperature nitrogen sorption methods. Estimation of the amorphous contribution by XRD has been compared with that estimated via sorption uptake using different probe molecules such as water, n-hexane, cyclohexane and benzene. The sorption uptake was found to be sensitive to the extent of amorphous content in the sample and to the characteristics of the probe sorbates. The sample with a 100% amorphous contribution as estimated by XRD methods exhibited lower values for this contribution when estimated by sorption techniques. The estimation of the amorphous contribution using benzene sorption data was found to be in excellent agreement with the amorphous contribution as estimated by XRD methods. A lower agreement was exhibited by the other sorbate probes studied

Monitoring the Hydrothermal Crystallization of Ga/ZSM-5 Using Sorption and other Conventional Techniques

Sorption techniques have been employed for monitoring progress in the hydrothermal crystallization of synthetic MFI-type gallosilicate from a (TEBA) 2 O–Na 2 O–Ga 2 O 3 –SiO 2 –H 2 O system at 453 K. The samples obtained at different stages in the crystallization process were also examined by other conventional techniques such as XRD, IR, TG/DTA, N 2 adsorption and chemical analysis. The influence of the crystallinity on the BET surface area and on the micropore void volume was examined using low-temperature nitrogen adsorption. The sorption uptake behaviour was studied on samples of varying crystallinity using different sorbate probe molecules such as water, n-hexane and cyclohexane. The amount of sorbate uptake was found to be sensitive to the crystallinity of the sample and the characteristics of the probe molecules employed. The crystallinity as estimated by XRD methods has been compared with that obtained by sorption uptake using different probe molecules. In comparison to other sorbates, the uptake of n-hexane was found to yield a more realistic estimation of the degree of crystallization of the intermediate phases. The crystallinity evaluated from the uptake of n-hexane was found to be in close agreement with that estimated by XRD methods as compared to the crystallinity evaluated using other conventional techniques. The correlation between the crystallinity obtained by sorption measurements and by other methods such as XRD, IR, TG/DTA and N 2 adsorption was discussed and compared

Sorption Properties of Cation-Exchanged Heulandite

Samples collected from the Aurangabad District, Maharashtra, India were characterized by XRD, IR, TGA and DTA methods, and by chemical analysis, as calcium-rich heulandite. Samples of potassium heulandite (K-Heu) and hydrogen heulandite (H-Heu) were prepared by ion exchange, their thermal stabilities being confirmed by XRD, IR, TGA and DTA methods. Water sorption studies were carried out at five different temperatures on the parent material (P-Heu) and on K-Heu and H-Heu. Different sorption models were tested on the data obtained and the corresponding results are reported

Sorption Properties of the Natural, K and Partially Deammoniated (H/NH) Forms of Clinoptilolite

A sample collected from the Aurangabad District, Maharashtra, India was characterized by XRD, IR, TG and DTA methods, and by chemical analysis, as a calcium-rich clinoptilolite. Two different methods involving exchange with KOH or NH 4 Cl led to the formation of K-clinoptilolite (K-Clino) and H/NH 4 -clinoptilolite (H/NH 4 -Clino). Water sorption studies were carried out on the parent clinoptilolite (P-Clino), K-Clino and H/NH 4 -Clino at five different temperatures in the range 303–423 K. Different adsorption models were applied to the data obtained from such sorption studies. Thermodynamic parameters such as the chemical potential were also computed from the sorption data and their significance is discussed

Influence of the Nature of the Non-Framework Cations on the Sorption Properties of Natural Stilbite

A natural zeolite of stilbite type, collected from the Deccan traps (Aurangabad, M.S., India), has been investigated for its selectivity sequence in exchanging extra-framework cations for the first time, using Ca 2+ , Sr 2+ , Ba 2+ , Mg 2+ , Na + and Ag + cations as the probe cations. The different cation-exchanged forms were characterised by X-ray powder diffraction, IR spectroscopy, TG/DTA, chemical analysis and water sorption capacity. Water sorption isotherms in the temperature range 303–393 K were obtained as a function of different non-framework cations up to a pressure of 22 Torr. The sorption data were analysed in terms of different sorption models. The characteristics and population of the non-framework cations were found to influence the chemical affinity for water sorbate almost in a similar trend