Zeolites sorption studies

Recent sorption studies tend to support this interpretation. Based on sorption studies on USY-zeolites, Lohse et al. (36) concluded that whole sodalite units are destroyed during the dealumination and rebuilding of the framework in USY-zeolites. Such sodalite units provide the silica necessary to fill the large number of framework vacancies left by dealumination. The consumption of whole sodalite cages leads to the formation of "secondary" pores (vide infra). 

Acid properties. The acid properties of zeolites, including those of aluminum-deficient zeolites, have been described in several reviews (e.g. 33-35). The methods used to study the acidity of aluminum-deficient Y zeolites include infrared spectroscopy (primarily pyridine and ammonia sorption studies), n-butylamine titrations in the presence of Hammett or arylmethanol indicators, and to a lesser extent potentiometric titrations and calorimetric measurements. 

Pyridine sorption studies have shown the presence of both Bronsted and Lewis acid sites in USY zeolites, although to a lesser extent than in the corresponding HY zeolite (51,53). Acidity is maintained even after strong dehydroxylation of USY-B at 820°C. Rehydration of the calcined material did not regenerate significantly Bronsted acid sites, due to irreversible changes in the zeolite framework (51). 

Pyridine sorption studies on EDTA-dealuminated Y zeolites at various temperatures (54,58), as well as measurements of differential heats of adsorption of ammonia on aluminum-deficient Y zeolites (57,59) have led to the conclusion that aluminum-deficient Y zeolites have stronger acid sites than the parent zeolite. 

Despite the fact that both normal and monomethyl-substituted paraffins readily enter the pores of ZSM-5 and ZSM-11, preferential sorption of the normal isomer is observed under thermodynamic equilibrium, non-kinetically controlled conditions. Whereas small-pore zeolites, such as 5A and erionite, totally exclude branched hydrocarbons, and large-pore zeolites exhibit little preference, the intermediate pore-size zeolites ZSM-5 and ZSM-11 show a marked preference for sorption of the linear paraffin, even under equilibrium conditions. Competitive liquid phase sorption studies at room temperature indicated selectivity factors greater than ten in favor of n-hexane relative to... 

The proposed model for non-isothermal sorption kinetics can quantitatively describe uptake0data for adsorption of i-octane on 13X and n-pentane on 5A zeolites. The study indicates that the principal resistance to mass transfer for these systems may be confined at the surface of the zeolite crystals. It is also found that the internal thermal resistance of the assemblage of the micron size zeolite crystals used in the kinetic test is significant which produces a substantial thermal gradient within the assemblage and slows down the heat dissipation from it. 

It is well-known in the special literature on zeolites that as a result of the partial or complete removal of aluminium, the sorption characteristics of zeolites are significantly altered. The adsorption of various polar vapours on so-called ZSM-5 zeolite was studied by Flaningen et al. in detail [53]. These authors pointed out that zeolite lattices free of... 

D. M. Ruthven (University of New Brunswick, Fredericton, N.B., Canada) I was interested in the conclusion that the density of intracrystalline water is similar to that of the bulk liquid. This agrees rather well with the conclusions of Dubinin et al. which are based on equilibrium sorption studies in NaX zeolite and also in other systems. 

Sorption of 2,2 -bipyridine (bpy) into the void space of Mm/nZSM-5 (m= 0, 3, 6 M= Na, Zn ", H" ) zeolites was studied by Raman spectrometry. The differences in the spectra obtained from the loaded zeolites have been rationalized in terms of probable conformation within the zeolite channels. It appears clearly that bpy conformation depends on the aluminum content of the framework, nature of cations and zeolite acidity, bpy occluded in silicalite-1 was found to be in the trans conformation. The non bonding interactions between the extraframework Na" cation and occluded bpy stabilize the cisoid non-planar conformer, whereas the coordination bonding between Zn " and N atoms constrains the cis planar conformation. In HZSM-5, bpy sorption results in both mono and diprotonation of bpy. 

The sorption of ethane, efoene and propane in silicalite-1 has been studied over foe temperature range 0-50 C. This study is part of a larger programme designed to establish foe preferred zeolite for foe s aration of specific pairs of lower saturated and imsaturated hydrocarixrns and their branched isomos by Pressure Swing Adsorption (PSA) methods. These studies are, of course, also of importance in foe development of a b er understanding of foe fundamentals of hydrocarbon/zeolite sorption interactions. 

The research on guest-inclusion complexes of calixarene based molecular crystals paved the way for different type of gas-sorption studies in these materials under various conditions. Although these materials generally dcai t possess uniform pore nor have high surface area (unlike traditional porous materials such as zeolite, molecular sieves or MOFs), their unique void structures make them attractive candidates for selective gas-sorption and separation applications. It should be noted that no uniform method were used to analyze the gas-sorption capacity (or separation capability) of these... 

FIGURE 3.16 (Left) Building blocks of FMOF-1 (middle) water sorption studies in FMOF-1, BPC-Carbon and Zeolite-5A (right) water and hydrocarbon sorption studies in FMOF-1 [111]. (Reproduced Irom Yang, C. et al., ChemSoc 133,18094 (2011), with permission). 

Poly (vinyl alcohol) (PVA) has also been applied to alcohol-water pervaporation. ZSM-5 was again utilized, and mixed-matrix enhancements resulted. The ZSM-5/PVA mixed-matrix membranes demonstrated increased selectivity and flux, compared to pure PVA, for the water-isopropyl alcohol separation. Membrane swelling and fluxes increase as the water concentration in the feed increases. " Sorption studies of ZSM-5/PVA systems indicate that this hybrid material is a good candidate for the extraction of water from alcohol. Modified poly (vinyl chloride) embedded with NaA zeolite has demonstrated both flux and selectivity enhancements for the ethanol-water separation at high zeolite loadings. Voids at the solid-polymer interface prevented seleetivity enhaneement at low zeolite loadings. ... 

Spectroscopy. In the methods discussed so far, the information obtained is essentially limited to the analysis of mass balances. In that re.spect they are blind methods, since they only yield macroscopic averaged information. It is also possible to study the spectrum of a suitable probe molecule adsorbed on a catalyst surface and to derive information on the type and nature of the surface sites from it. A good illustration is that of pyridine adsorbed on a zeolite containing both Lewis (L) and Brbnsted (B) acid sites. Figure 3.53 shows a typical IR ab.sorption spectrum of adsorbed pyridine. The spectrum exhibits four bands that can be assigned to adsorbed pyridine and pyridinium ions. Pyridine adsorbed on a Bronsted site forms a (protonated) pyridium ion whereas adsorption on a Lewis site only leads to the formation of a co-ordination complex. 

Without any doubt, the zeolite framework porous characteristics (micropores sizes and topology) largely govern the zeolite properties and their industrial applications. Nevertheless for some zeolite uses, as for instance, host materials for confined phases, the zeolite inner surface characteristics should be precised to understand their influence on such low dimensionality sorbed systems. In that paper, we present illustrative examples of zeolite inner surface influence on confined methane phases. Our investigation extends from relatively complex zeolite inner surface types (as for MOR structural types) to the model inner surface ones (well illustrated by the AFI zeolite type). Sorption isotherm measurements associated with neutron diffraction experiments are used in the present study. 

The present study concerns the interaction of propene molecules with cobalt sites in CoZSM-5. The experiments of CO and NO sorption evidenced that this zeolite contained practically only Co2+ in exchange position and Co3+ in oxide form. Propene is a reactant in several reactions catalyzed by cobalt containing zeolites (like reduction of NO, amonoxidation of propene and others). 

Even if 5A zeolite is widely used in iso-paraffin separation from an n/iso paraffin mixture, the adsorbent is affected by a slow deactivation mainly due to coke formation inside the molecular sieve porosity. Its aging phenomenon decreases its sorption properties. According to previous studies, 5A zeolite deactivation results essentially from heavy carbonaceous compound formation in a-cages blocking the 5A zeolite microporosity [1-2]. 

The same study has been performed concerning the methane / ZSM-12 zeolite system. The neutron diffractograms, measured for different methane loadings of ZSM-12 zeolite, are represented on figure 9. In addition, a methane calibration sorption isotherm... 

Tin incorporated mesoporous Sn-MFI catalysts with different Si/Sn ratio using microwave were synthesized with carbon as hard template. These tin MFI catalysts were characterized using various physicochemical techniques XRD reviled the formation of more crystalline MFI structures which was further supported by the SEM and TEM imaging which clearly showed well ordered zeolite single crystals with mesoporosity. The N2 sorption isothers reviled the formation of bimodal mesoporous zeolites and the presence of tin in tetrahedral site was confirmed by FTIR (970 cm 1) and XPS (3ds/2 and 3 dj 2 electronic states). The thus synthesized mesoporous Sn-MFI catalysts with different Si/Sn ratios were used in studying the catalytic Baeyer-Villiger Oxidation (BVO) of cyclic ketones... 

Sorption. Lohse et al. (36,47,48) have studied the sorption properties of acid-dealuminated Y zeolites that contain about 99% SiC, and compared them with those of the... 

Sorption. The sorption properties of aluminum-deficient mordenite are strongly affected by the dealumination procedure used and by the degree of dealumination. Materials prepared by procedures that do not involve high temperature treatments show a relatively high sorption capacity for water (15,70), due to the presence of silanol groups, which are hydrophilic centers. However, aluminum-deficient mordenite zeolites prepared by methods requiring heat treatment show a lower sorption capacity for water due to fewer silanol groups. This was shown by Chen (71), who studied the sorption properties of aluminum-deficient mordenite prepared by the two-step method. 

The zeolites and catalysts used in this study were prepared as described previously (1,16,18,20). The ortho-xylene sorption rate data, obtained on a computer-controlled Du Pont 951 TGA, were measured at 120°C and P(o-xylene) 3.8 torr. The isomerization and disproportionation data were obtained using a... 

Dispersion of POMs onto inert solid supports with high surface areas is very important for catalytic application because the surface areas of unsupported POMs are usually very low (—10 m2g). Another advantage of dispersion of POMs onto inert supports is improvement of the stability. Therefore, immobilization of POMs on a number of supports has been extensively studied. Silica and active carbon are the representative supports [25], Basic supports such as MgO tend to decompose POMs [101-104], Certain kinds of active carbons firmly entrap POMs [105,106], The maximum loading level of POMs on active carbons is 14 wt% [107], Dispersion of POMs onto other supports such as zeolites, mesoporous molecular sieves, and apatites, is of considerable interest because of their high surface areas, unique pore systems, and possibility to modify their compositions, morphologies, and sorption properties. However, a simple impregnation of POM compounds on inert supports often results in leaching of POMs. 

Thermogravimetry can be used to measure the amount of water [232] or other molecule adsorbed on a zeolite. DSC can be uhlized to study the thermal effects during adsorption and desorphon of water [233] because the peak area under the heat flow time curve is related to the sorption heat. 

---