The CO2 capture represents a major technical challenge to fight against global warming. Adsorption is an interesting alternative for CO2 capture. The use of oxides to enhance the CO2 adsorption over zeolites is largely pointed out in the literature. This study, dedicated to MgO-impregnated NaY zeolite, is based on CO2 adsorption and desorption over this adsorbent at various MgO rates (2, 5, 10, and 15 %) via in situ FTIR spectroscopy. This later provides very useful information about the physisorbed and chemisorbed CO2 according to MgO impregnation rate. FTIR investigation, based on adsorption at 25 degrees C of low and high doses of CO2, then followed by desorption under vacuum at 25, 100, and 200 degrees C, indicates that CO2 is physically adsorbed on cationic sites and chemically in the form of carbonates. The major carbonate species formed are bicarbonate, unidentate, chelated and bridged bidentate carbonate as well as carboxylate species. The results show that the chelated bidentate carbonate, and carboxylate species are the most resistant to desorption, which is related to both basicity and accessible porosity. In addition, this investigation highlights the heterogeneity of zeolites due to the formation of various adsorption basic sites.

In absolute ethanol production, LTA zeolites (3A and 4A) are industrially used because of their selectivity and affinity to water. Despite the numerous studies performed on these materials, a lack of data is encountered, particularly at the gaseous phase. This study contributes to the understanding and elucidation of the behavior of water and ethanol adsorbed separately over 3A, 4A and 5A zeolites. Using TGA measurements in dynamic mode, this study focuses on the investigation of temperature effect (T = 20-45 degrees C) on the adsorption kinetics of water and ethanol. The comparison of the adsorption properties of the three zeolites shows a particular behavior of the 3A, which is characterized by both the higher water uptake and the specific affinity reflected by the initial adsorption rate and the diffusion coefficient. Based on some previous studies, which point out that ethanol may be adsorbed on 3A, this investigation shows the role of water traces in the "ethanol" uptake. The comparison of the water and ethanol kinetics at various temperatures leads to estimate the optimal selectivity temperature. On the other hand, the modeling study using four kinetic models highlights the good fitting of pseudo-first order from which the adsorption activation energies are deduced.

Adsorption isotherms of CO2 are volumetrically measured at temperatures close to ambient (30, 35, 40 and 45 degrees C) over MgO impregnated NaY zeolites, in order to highlight the effect of MgO impregnation rate on the adsorbed quantities. XRD analysis displays a good preservation of the zeolitic structure after impregnation. Textural parameters are determined by both adsorption-desorption isotherms of N-2 at -196 degrees C and adsorption isotherms of CO2 at 30 degrees C. The result of the impregnation rate effect shows that 2% of MgO seems to be the better rate for the capture of CO2. This is confirmed by the evolution of isosteric heats, which reveals a high strength interaction and heterogeneity of zeolitic sites adsorption. The modeling of CO2 adsorption isotherms based on various isotherms (single-site Langmuir, dual-site Langmuir, multi-site Langmuir, Sips, Jensen-Seaton, Toth, UNILAN and Freundlich) highlights a good correlation with all models based on the hypothesis of heterogeneity of adsorption sites.

In this study, thermal and calorimetric techniques are used in order to get a better insight into the progress of the carbonization process of a lignocellulosic material for activated carbon preparation. Therefore, the pyrolysis process of the precursor (olive waste) alone and in the presence of the activating agent (ZnCl2) at different temperatures is followed via thermogravimetry–mass spectroscopy analysis. The mass loss and the temperature programmed desorption profiles of the signals m/e = 16, 18, 28, 30, and 44 allow the determination of the role of the activating agent during the synthesis of the activated carbons at different temperatures. In order to follow the changes in energy during the pyrolysis process, differential scanning calorimetry is used. The obtained results are linked to the properties of the activated carbons obtained at the different temperatures and characterized in a previous paper. In this manner, it is possible not only to determine the thermal events taking place during the pyrolysis process but also to unravel their impact on the textural, structural, and surface properties of the final materials.

This study aims at investigating the relationship between the porosity and the surface functional groups of an activated carbon during the pyrolysis process. Several activated carbons are prepared by the carbonization of a mixture of olive waste and ZnCl 2 at different temperatures, which are chosen by taking into account the different phenomena occurring during this treatment. The porosity of the prepared carbons is investigated using both N 2 and CO 2 isotherms at 77 and 273 K, respectively. Long-range and short-range orders are studied respectively by X-ray diffraction (XRD) and Raman spectroscopy. The investigation of the carbon functionalities is carried out by Boehm titration, Fourier transformed infrared spectroscopy (FTIR) and water adsorption measurements. The effect of carbonisation temperature on the adsorption of cyclohexane provides additional information on the oxygen functional groups and especially the carboxylic proups. To summarize, the results show that a carbonisation at 573 K is sufficient to obtain a well-developed porosity and to ensure already the formation of acidic surface groups and especially the carboxylic groups.

Two activated carbons are prepared by chemical activation of olive residue using zinc chloride. The first sample is cooled down slowly after the carbonization in the furnace under a flow of nitrogen, while the second is directly removed from the furnace just after the carbonization and put at ambient temperature and pressure. The textural and structural characteristics of the two samples are determined by nitrogen adsorption at 196 degrees C and X-ray diffraction (XRD). The oxygen functional groups are characterized via Boehm's titration and Fourier transformed infrared spectroscopy (FTIR). The cooling down step at different rates is followed by thermogravimetry mass spectroscopy analysis (TG/MS). Slow cooling down of the sample after carbonization leads to CO2, O-2, and CO consumption creating more active sites, which are responsible of the formation of surface oxygen groups, and especially carboxylic groups. The latter dramatically enhance water vapor adsorption at low relative humidity. The cyclohexane adsorption on activated carbons, which is carried out by thermogravimetric analysis (TGA), shows that the cooling down step has an effect on both the initial rate of adsorption and the adsorption uptake at equilibrium. (C) 2015 Elsevier Inc. All rights reserved.

Ag- and Zn-exchanged A zeolites are prepared by the liquid ion exchange method following the procedure reported in our previous studies. Samples with Ag and Zn metal loadings are obtained and characterized by physicochemical and thermal analyses. The obtained materials with improved physicochemical properties are promising candidates for use as haemostatic agents. Both powder X-ray diffraction and nitrogen adsorption measurements show good conservation of the zeolitic structure and texture after ionic exchange. Porosity measurements indicate that the variation of the porous volumes and the specific surface areas depends on the number and nature of exchanged cations. Thermal behavior of water adsorption studied by using TGA microbalance and differential scanning calorimetry highlights clearly the complexity of the adsorption and diffusion mechanisms of water molecules within the micropores of exchanged zeolites. The differences between sorption rates and hydration heats appear to be due mainly to the location and migration of Ag, Ca and Zn species in the cationic position of the A zeolite framework. The exothermicity of adsorption is attenuated by Ag and Zn exchange. (C) 2014 Elsevier Inc. All rights reserved.

Two samples of an activated carbon are heat treated at 500 °C for 2 h under a flow of inert gas. The only difference between the treatments of the two carbons is the cooling down step. After these treatments, the two carbons were hydrophobic and presented similar adsorption properties and an identical behavior toward water and cyclohexane uptakes. After being stored in ambient conditions for 20 months, the stability of oxygen functional groups is studied. The quantification of various oxygen groups is done by Boehm’s titration and by thermogravimetry–mass spectroscopy analysis. It is found that the creation of oxygen groups, especially carboxylic acids, which are very attractive to water molecules, depends on the cooling down step. This is confirmed by both water isotherms and cyclohexane breakthrough measurements. Cyclohexane breakthrough times show that one of the heat treated carbons does not preserve its hydrophobic character compared to the other carbon, which presents a breakthrough time value close to that obtained before the storage.

Activated carbon obtained from olive waste is modified via heat treatment at several temperatures (300, 400, 500, 600 and 700°C) and under inert atmosphere in order to remove carboxylic surface functions. The porous structure characteristics of all samples are determined by nitrogen adsorption at −196°C. Changes in surface carboxylic groups resulting from the heat treatment are examined via various techniques including Boehm’s titration, thermogravimetric analysis (TGA), Fourier transformed infrared spectroscopy (FTIR) and thermogravimetry–mass spectroscopy analysis (TG/MS). The improvement in performance highlighted by both cyclohexane and humidity uptake is quantified using TGA and breakthrough time measurements under different conditions. A heat treatment at 500°C leads to a release of CO2 following the elimination of carboxylic acid functions and to a carbon with higher hydrophobicity. Above 500°C, in addition to CO2, there is a release of CO, which results from the decomposition of other surface organic functions. This affects negatively the textural properties.

NaX zeolite, Algerian bentonite, their mixtures, and their Cs-exchanged forms are subjected to heat treatment at different temperatures (800, 1000, and 1100°C) and γ-irradiation doses varying from 100 to 1000kGy. The effects of these treatments on structural and textural properties of the above materials as getters of radionuclides are studied using powder X-ray diffraction (XRD), nitrogen adsorption surface analyzer, and scanning electron microscopy (SEM). A thermal treatment of NaX and CsNaX zeolites up to 1000°C results in the formation of new crystalline phases (nepheline and carnegieite). In contrast, bentonite becomes totally amorphous when it is heat treated up to 800°C. Heat treating of zeolite–bentonite mixtures gives rise to partial amorphisation. γ-Irradiation of the studied materials reveals a good resistance of the Cs exchanged NaX zeolite. This is due to its higher basic character resulting from the Cs2O formed by the reaction between Cs+ present in the zeolite and the O2− anion liberated after γ-irradiation.

Ag- and Cu-exchanged forms of HY zeolite are prepared by the solid-state ion exchange (SSIE) technique. Samples with different metal loadings ranging from low to high exchange are obtained. Both compositional and structural investigations of the exchanged zeolites are performed by elemental analysis, powder X-ray diffraction (XRD), and nitrogen adsorption porosimetry. The acidity investigation is carried out by using the Fourier transform infrared spectroscopy (FTIR) of pyridine adsorption. Propene adsorption over the Ag- and Cu-exchanged zeolites is studied at room temperature by using in situ FTIR spectroscopy. XRD analysis shows good conservation of the zeolitic structure after ionic exchange even at high exchange degree. Porosity measurements indicate that the increase of Ag and Cu exchange degrees leads to a decrease of the porous volumes and the specific surface areas, which is more pronounced for Ag-exchanged zeolites. The acidity evaluation for both exchanged metals shows an important decrease of Brønsted acidity and a slight increase of Lewis acidity, which are more noticeable at high degree of exchange. Instantaneous oligomerization of propene on HY zeolite at room temperature is favored by the relatively high amount of Brønsted acid sites. The propene molecules interact more strongly with Cu2+ than with Ag+. The shape of the CC stretching band of the FTIR spectra involves at least two overlapping bands indicating that the propene CC bond may interact with several kinds of Ag+, Cu2+ and Cu+ sites of various propene bonding.

Pure crystalline NaX zeolites with Si/Al = 1.2 is prepared by the hydrothermal method. The modification is achieved by following the conventional ion-exchange technique to obtain Ag- and Cu-exchanged forms of NaX zeolite with different metal loadings ranging from low to high exchange. Compositional and structural investigations of all samples are performed by atomic absorption spectrometry, elemental analysis, powder XRD, and nitrogen adsorption porosimetry. The acidity of all exchanged zeolites is investigated using both the ammonia temperature-programmed desorption (NH3-TPD) carried out by microbalance, and the pyridine adsorption performed via Fourier transform infrared spectroscopy (FTIR). XRD analysis shows the global conservation of the zeolitic structure after ionic exchange. The crystallinity loss is more important for zeolites exchanged at high degree of copper. Porosity measurements indicate a decrease of the porous volumes and the specific surface areas when the Ag or Cu exchange degree is raised. Mesopores particularly appear at high exchange degree of copper. NH3-TPD indicates that the increase of Ag and Cu-exchange degrees leads to an increase of the global acidity, which is more pronounced for Cu-exchanged zeolites. The strength of acid sites for Ag-exchanged zeolites is weaker than for Cu-exchanged zeolites. The FTIR spectroscopy analysis by pyridine adsorption confirms the formation of extra framework aluminum (EFAL) species, inducing an increase in the concentration and the strength of the Lewis acidity. The formation of EFAL is more important for Cu-exchanged zeolites.

The present work is devoted to study the short-time reactor neutron irradiation of yttria stabilised zirconia (YSZ) at 315 K. The samples were prepared by the reactive calcination method and characterised by X-ray diffraction (XRD) analysis and scanning electronic microscope. The prepared samples were irradiated by reactor neutrons at different exposure times and investigated by XRD analysis. The results obtained show good radiation resistance of YSZ to reactor neutron irradiation.

Adsorption and diffusion kinetics of propane and pentane on CaA molecular sieves having different degrees of calcium exchange (0, 33, 44, 57 and 75% of Ca(2+)) have been studied using thermobalance under constant pressure of 27kPa and 373 and 523K. The results obtained show clearly the effect of calcium exchange on parameters such as the adsorbed quantities, the initial rates of adsorption and diffusion coefficients. Despite the smaller size of propane molecule, the pentane is more adsorbed and its initial rate of adsorption is more important. This is related to the stronger interaction molecule/wall of zeolite alpha cavity. Using the model resulting from second Fick's law, a good concordance appears between theoretical and experimental curves of diffusion.

Adsorption of n-pentane, n-hexane and isopentane on 5A zeolite was studied using a microbalance at 100, 250 and 420°C (P = 27kPa). The analysis of the compounds trapped in 5A zeolite pores shows a relation between the formation of a carbonaceous compound and an inconsistency between experimental rates of uptake and theoretical curves using the Fick’s second law for diffusion.

Separation processes using selective adsorption on zeolite are widely applied in chemical industries. The X zeolite is especially used for the separation of xylenes isomers. The objective of this work-based on NaX adsorbent known by its selectivity exclusively geometric to xylene isomers-is a contribution to the comprehension of the separation mechanisms and of the steric effect parameters. Adsorption of o-xylene, m-xylene, p-xylene, and trimethylbenzene was studied in thermobalance at 100, 250, and 420 degreesC and at a constant pressure of 700 Pa. The results show that the adsorption and diffusion process are strongly influenced by the molecules' sizes. Using the Fick law plot, disruption phenomena owing to the steric effect were observed when the supercages of NaX adsorbent were filled.

Abstract. The sensitivity based on the resistive effect of porous BaTiO 3 ceramic samples were studied at 500°C using a characterization setup of potentiometeric type. We have shown that these porous materials, fabricated by adding anthracene using solid and liquid techniques, exhibit semi-conductivity of p type expressed in terms of an increase in resistivity under N2 and a decrease under O2. The pore sizes play an important role in the speed response of N2. Depending on the atmosphere (N2 or O2), the behavior of these materials is related to the established oxygen equilibrium between this atmosphere and BaTiO 3 perovskite surface.

Adsorption of propene, isobutene and isopentane on 5A zeohte was investigated using a microbalance at temperatures between 50 and 420degreesC. From alkenes, the amount adsorbed at saturation (i.e. after 100h) increases with temperature whereas from isopentane, the weight adsorbed decreases with increasing the temperature from 50 to 250degreesC, then slightly increases for higher temperatures. From alkenes, the organic material irreversibly trapped at low temperatures (80-150degreesC) in the micropores of 5A zeohte is mainly constituted of oligomers formed on the acid sites of this zeohte and located in their a cages. Their effects on the adsorption capacity are more pronounced for isobutene due to their preferential location in the cages near the outer surface of the crystallites. At high temperatures (350-420degreesC), aromatic and polyaromatic molecules are formed. From isopentane, only isopentane are found in the organic material trapped at low temperatures (50-150degreesC) showing that the desorption of this molecule from the narrow pores of 5A zeolites is very slow. These isopentane molecules occupy a large part of the pore volume causing a decrease in the adsorption capacity of the zeolite. At higher temperatures, part of trapped isopentane molecules is transformed on the weak acid sites of 5A zeohte into oligomers and aromatic compounds.

Adsorption of isopentane and n-pentane on 5A zeolite was investigated using a microbalance at temperatures between 50 and 420 degreesC (P-alkanes = 97 kPa). Analysis of the the adsorbed phase shows that, despite the well-known geometric selectivity of 5A zeolite, isopentane enters the pores and remains trapped in the alpha cages. At saturation at 50 degreesC, all the alpha cages of the 5A zeolite are occupied by three isopentane molecules. Isopentane molecules are completely removed from the zeolite pores by an adequate vacuum treatment at the adsorption temperature. At high temperature (T greater than or equal to 250 degreesC), trapped isopentane molecules ave transformed into "coke" (oligomers and aromatic compounds) by successive reactions (cracking, polymerisation, cyclisation and hydrogen transfer) on the acid sites of 5A zeolite. The "coke" molecules, blocked inside the alpha cages, limit the desorption of isopentane (and n-pentane).

The formation of carbonaceous compounds <> from propene and isobutene on 5A zeolites with different degrees of calcium exchange (55,75 and 85%) and their effects on the capacity for nitrogen adsorption were investigated in a microbalance system. The operating conditions of coking were as follows: 150 and 350 degrees C, pressure of alkene of 97kPa, 0.085g of zeolite and operating time from 2 min to 24h. The higher the temperature and the degree of exchange, the faster the coke formation. Coke constituted mainly by oligomers at 150 degrees C and of aromatics (alkylbenzenes and alkylnaphthalenes) at 350 degrees C are trapped in the a cages. The significant decrease in the pore volume accessible to nitrogen due to coke showed that whatever their origin, coke molecules are preferentially located in the outer part of the crystallites.