Authors:Judit Varga, Á. Fudala, J. Halász, and I. Kiricsi
The solid-state ion-exchange procedures of zeolites with Cu2+, Ni2+, Fe2+ and Co2+ salts can be resulted in prosperous catalysts for NO decomposition. Reactions taking place in solid-state between four transition metal cholirides and H-ZS-5 zeolite were investigated by means of a derivatograph. The results showed that irreversible consumption of surface -OH groups occurred with simultaneous bonding of the transition metal in the zeolite channel structure.
The western region of the Deccan Volcanic Province (DVP) is constituted of tholeiitic lava flows. They host numerous cavities,
varying in size and shape, largely occupied by zeolites and a variety of secondary minerals, amongst which the fibrous zeolites
(natrolite group), are particularly gorgeous and attractive. Scolecite and mesolite are the only two members commonly occurring
in this region. Our data on their thermal behaviour significantly differs from that reported in previous literature. Scolecite,
Ca8(Al16Si24O80)·24H2O shows three distinct steps instead of two and water loss is observed even beyond 550°C. It is held that the first step corresponds
to the expulsion of water from the site farthest away from Ca and the next two steps in succession correspond to the two sites
nearer to Ca. Mesolite, Na16Ca16(Al48Si72O240)· 64H2O has much more complex behaviour with four or five steps of water expulsion and a major loss around 248–270°C in a double
reaction attributed here to the expulsion of water from scolecite type channels. It is further held that the natrolite type
channels are emptied in further steps. Loss of water in steps even beyond 400°C is particularly noted and such reactions are
well reflected in the TG and the DTG. Peak temperature dependence on sample amounts is also evident. Successive phase transformations
above 700°C, up to 1000°C are reflected in the DTA curves.
A procedure for measurement of the heat of zeolite dehydration by scanning heating has been designed. Simultaneous data on heat flow (DSC) and mass loss (TG) are required for evaluation. The heating rate depends on the experimental conditions (point-spread function, sample mass, crucible design, and calorimetric reproducibility). Dehydration measurements have three advantages as compared with the sorption procedure: i) one can investigate samples with irreversible dehydration; ii) no approximation model is needed for calculation of the partial molar heat of dehydration; and iii) the procedure is not labor-consuming.The procedure was tested on the natural zeolites heulandite, chabazite and mordenite. The results are close to those measured by the sorption procedure. The partial molar heat of dehydration was found to depend on the water content. It increases from 50 to 87 J mol–1 K–1 for heulandite, from 53 to 81 J mol–1 K–1 for chabazite, and from 51 to 71 J mol–1 K–1 for mordenite.The approximation of the heat of sorption by linear regression was found to be wrong. Detection of a phase transitioN after this approximation has no meaning.
Derivatographic and calorimetric measurements were used to study the thermal properties of combined inclusion compounds of
zeolite-cyclodextrin type and of zeolite-cyclodextrin-pharmaceutical type. There were differences in the characteristic decomposition
temperature intervals and in the modes of cyclodextrin and pharmaceutical liberation from the products. Calorimetric measurements
revealed that the process in the newly-formed complex host is connected with a glass transition.
The products are intended for use in veterinary medicine.
Authors:B. Hunger, M. v. Szombathely, J. Hoffmann, and P. Bräuer
Desorption energy distributions were calculated for temperature-programmed desorption (TPD) of ammonia from H zeolites of
different type by means of regularization. This method does not require any limiting assumptions about the distribution function.
It could be shown that the desorption energy distributions obtained are nearly independent of the experimental conditions
and therefore they should represent a suitable measure for the distribution of the strength of acidic sites. The calculated
desorption energy distributions for the ammonia desorption from the isolated bridging SiOHAl groups of H zeolites of different
type significantly differ from each other in shape. The increase of the desorption energy of the main range of the distribution
functions correlates well with the increase of the average acid strength of the SiOHAl groups with decreasing Al content of
Authors:P. Llewellyn, N. Pellenq, Y. Grillet, F. Rouquerol, and J. Rouquerol
Water adsorption at temperatures of 286 and 296 K on silicalite-I, ZSM-5 (Si/Al=16), ZSM-48 (Si/Al=50) and AlPO4-5 is followed by gravimetry with a quasi-equilibrium continuous adsorptive introduction.
The results show that all of these samples are characterized by a continuous distribution of strongly energetic water adsorption
sites (from 60 to 120 kJ·mol−1) for which the adsorption is irreversible at the experimental temperature. This probably justifies the presence of hysteresis
on desorption at very low relative pressure values. Adsorption of water in these systems firstly occurs by site. This is then
followed by cluster formation and it is suggested that it is the ability of the adsorbent to build up these clusters within
the microporous structure which determines intracrystalline uptake. It is put forward that the zeolites, silicalite-I and
ZSM-5, do not accommodate cluster formation within its microporous network. However, an external flexible microporous structure,
containing Lewis sites, may be present for large crystals. This flexible secondary structure may then be able to opened (swelled)
at high relative pressures.
On the other hand, for the aluminophosphate AlPO4-5, it is believed that a change in the aluminium coordination on the formation of a crystal hydrate together with capillary
condensation results in a large step in the adsorption isotherm, which is itself preceded by a smaller step, revealing a brutal
densification of the adsorbed phase.
Authors:Sheng-Hung Wu, Chu-Chin Hsieh, Chung-Cheng Chiang, Jao-Jia Horng, Wei-Ping Pan, and Chi-Min Shu
effects on human health, cause odorous nuisances, and participate in photochemical reactions. The purification of industrial waste gases containing VOCs plays an important role in chemical engineering [ 1 – 4 ]. Activated carbon, zeolite, silica gel, and
Authors:Jamal Eldin F. M. Ibrahim, Emese Kurovics, Mohammed Tihtih, and László A. Gömze
insulated materials can reduce global warming and contribute to sustainability by reducing heat gain and loss through the walls [ 7 , 8 ].
Natural zeolites are microporous materials of volcanic origin. They are a well-known group of hydrated