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Zeolite (ZSM-5 or Y)/polystyrene (PS) composites were obtained by casting evaporation with different proportions (wt/wt) using ethyl acetate as the solvent. The films were characterized by XRD, SEM, water absorption, TG, DSC, and TMA (penetration mode). XRD revealed characteristic peaks of incorporated zeolites. Zeolite microdomains in the polystyrene films were detected by SEM. Water absorption was small, keeping practically constant after 4 h of immersion. TG showed increasing thermal stability of the composites compared to that of the pure PS. DSC revealed no significant changes on glass transition temperatures (Tg). The TMA curves with a 10 mN load showed expansion of composites up to the softening temperature (Ts) and compression of PS film. The Ts data did not show important changes, except for 20 wt% zeolite films. TMA results with a 100 mN load did not present any expansion, but the Ts values were much higher compared to the polystyrene film.

The acidity of heteropolytungstic acids containing cesium is of great interest because of their unique catalytic and physical properties. Preparation and characterization of Cs x H 3− x PW 12 O 40 ( x = 1, 2, 2.5 and 3) have been performed using FTIR for functional groups, XRD for crystal structure, 31 P MAS NMR for the environment of the phosphorous. Calorimetry and adsorption of pyridine interaction in cyclohexane slurry (Cal–ad method) was used to quantify the number of acid sites and the corresponding enthalpy of adsorption. The distribution of proton and cesium ions in the salt structures is nearly homogeneous, as confirmed by XRD, 31 P MAS NMR and enthalpy measurements. The acidity, systematically obtained in this work, indicates different proton strengths, with the following order: H 3 PW > Cs 2 HPW ≅ Cs 2.5 H 0.5 PW > CsH 2 PW ≫ Cs 3 PW, with Δ H 1 = −32.7, −28.3, −27.4, −20.8 and −7.8 kcal mol −1 , respectively. These enthalpies are strongly influenced by an endothermic term related to interstitial expansion of the structure by entrance of the pyridine molecule, which is evidenced by XRD results. The total amount of protons titrated by pyridine in all solids is larger compared to the calculated population on surface. This supports penetration by the polar probe into all of the solids. For Cs 2.5 H 0.5 PW the strongest protons are exposed nearly exclusively on the surface of this solid, as demonstrated by Cal–ad results for site-1 calculation. The combination of FTIR and adsorption site density demonstrated the effect of substituting Cs for H, changing the Bronsted acid site density to hydrogen-bonded ones.

The adsorption of indigo carmine dye onto chitin and chitosan from aqueous solutions was followed in a batch system. The ability of these materials to adsorb indigo carmine dye from aqueous solution was followed through a series of adsorption isotherms adjusted to a modified Langmuir equation. The maximum number of moles adsorbed was 1.24 +/- 0.16 x 10(-5) and 1.54 +/- 0.03 x 10(-4) mol g(-1) for chitin and chitosan, respectively. The same interactions were calorimetrically followed and the thermodynamic data showed exothermic enthalpic values of -40.12 +/- 3.52 and -29.25 +/- 1.93 kJ mol(-1) for chitin and chitosan, respectively. Gibbs free energies for the two adsorption processes of indigo carmine dye presented a positive value for chitin and a negative one for chitosan, reflecting that dye/surface interactions are thermodynamic favorable for chitosan and nonspontaneous for chitin at 298.15 K. The interaction processes were accompanied by an increase of entropy value for chitosan (90 +/- 6 J mol(-1)K(-1)) and a decrease for chitin (-145 +/- 13 J mol(-1)K(-1)). Thus, dye/chitosan interaction showed favorable enthalpic and entropic processes, reflecting thermodynamic stability of the formed complex, while dye/chitin interaction showed an exothermic enthalpic value and a highly nonfavorable entropic effect, resulting in a nonspontaneous thermodynamic system.

The interaction of hydrophobic chitin and chitosan with sodium dodecyl sulfate (SDS) has been studied by titration calorimetry at 298.15K. The nature of interaction of the surfactant and biopolymers was followed by enthalpy interaction profiles. The mixing enthalpy curves were determined by mixing SDS solutions above their critical micelle concentration with chitin and chitosan suspensions in different concentrations. The Gibbs free energy of aggregation values were -23.21, -22.71 and -21.53 kJ mol(-1) for chitin in 0.02, 0.05 and 0.1% concentration, respectively, and 28.30, 24.38 and 24.20 kJ mol(-1) for chitosan in 0.02, 0.05 and 0.1% concentration, respectively. The critical aggregation concentration (cac) obtained by calorimetric data gave 6.32, 7.07 and 9.14 mmol kg(-1) in 0.02, 0.05 and 0.1% concentration, respectively, for chitin and 2.09, 4.91 and 5.11 mmol kg(-1) for chitosan in 0.02, 0.05 and 0.1% concentration, respectively.

A recent article claims that the Cal–Ad method cannot discriminate multiple acid sites in the analysis of the interaction of pyridine (dilute pyridine in n -hexane) with HZSM-5. The Cal–Ad technique measures the enthalpy of a base-displacement reaction, while gas–solid calorimetry is a measure of an adduct formation between pyridine and the solid. A Born–Haber cycle with the appropriate values can demonstrate that the enthalpies derived from gas–solid calorimetry are an average of the two enthalpies of the interaction of pyridine with the two acid sites observed with the Cal–Ad method.

This report investigates the causes of the unique properties and reactivity of the titanium silicalite TS-1, a commercial zeolite containing 1% Ti by weight. The combined analysis of calorimetric and adsorption data, cal−ad, for the reaction of TS-1 with pyridine shows the absence of the strong acid site found in HZSM-5 and the presence of only 0.07 mmol g-1 of a −15.1 kcal mol-1 hydrogen-bonding site. Titrations with 2,6-lutidine indicate the same number of hydrogen-bonding sites with a lower enthalpy (−9.8 kcal mol-1). The magnitude of these enthalpies indicate that the acceptor sites are hydrogen-bonding sites that are comparable in acidity to the strongest sites on silica gel. The small amounts of these sites, 0.07 mmol g-1 compared to 0.8 mmol g-1 in silica gel and 0.5 mmol g-1 for the hydrogen-bonding sites of HZSM-5, account for the lower affinity of TS-1 for water. The absence of strong acidity prevents epoxide ring opening and explains the utility of TS-1 in epoxidation. Comparison of the results...

The cal-ad analysis of HZSM-5 provides a novel characterization of the donor-acceptor properties of this solid acid showing 0.0415 mmol per g of a strong Bronsted site and 0.53 mmol per g of a weak...

Adsorventes ZSM-5 impregnados com Nb2O5 foram aplicados na remoção de enxofre sob a forma de tiofeno, substância refratária de difícil remoção dos combustíveis líquidos. Para tanto, foi preparado um combustível modelo contendo iso-octano contaminado com tiofeno nas concentrações de 877,5 a 1155 ppmw. As amostras foram caracterizadas por difratometria de raios X (XRD), espectroscopias no infravermelho (FTIR) e Raman (FT-Raman) por transformada de Fourier para confirmação dos adsorventes obtidos, sendo priorizado o estudo de adsorção com aquele contendo 5% de pentóxido de nióbio, que apresentou uma maior capacidade de remoção de tiofeno. Os melhores resultados de adsorção foram alcançados a 353 K, sendo observado um maior tempo para atingir o equilíbrio. Sob essas condições, o melhor ajuste cinético foi alcançado utilizando a equação de pseudo-segunda ordem, evidenciando o domínio do fenômeno de quimissorção. Por outro lado, sob menores temperaturas, o modelo de difusão apresentou uma melhor aproximação dos resultados experimentais. O aumento da temperatura também favoreceu os processos espontâneos. ZSM-5 adsorbents impregnated with Nb2O5 were applied in the sulfur removal in the form of thiophene, refractory substance of difficult removal of liquid fuels. For this purpose, a model fuel containing iso-octane contaminated with thiophene in concentrations of 877.5 to 1155 ppmw was prepared. The samples were characterized by X-ray diffractometry (XRD), Fourier transform infrared (FTIR) and Fourier transform-Raman (FT-Raman) spectroscopies for confirmation of the adsorbents, being prioritized the adsorption study with that containing 5 wt.% of niobium pentoxide, because it showed a greater capacity for removal of thiophene. The best results of adsorption were achieved at 353 K, a longer time to reach equilibrium was observed. Under these conditions, the best kinetic fitting was achieved using the equation of pseudo-second order, demonstrating the domain of the phenomenon of chemisorption. While under lower temperatures, the diffusion model presented a better approximation of the experimental results. Also, the increasing of temperature did enhance spontaneous processes.

Polyoxometalates are large metal–oxygen nanostructured compounds that can be modified at the molecular level. Catalysts based on 12-tungstophosphoric acid (H3PW12O40) supported on different carries such as silica, silica–alumina, zirconia, and mesoporous MCM-41 have been successfully prepared and characterized by several physicochemical techniques (e.g., FTIR, FT-Raman, 31P MAS-NMR, calorimetry, thermal analysis, TPD of pyridine). The materials were tested in different reactions: transalkylation of benzene with aromatics, esterification of acetic acid and ethanol, esterification of oleic acid with ethanol, and cyclization of (+)-citronellal. The results, coupled with other applications of heteropoly acids in the literature, illustrate the potential for these catalysts to be used in greener processes, i.e., a more effective, selective, economical, and environmentally benign technique. The effects of support interaction, loading of H3PW12O40, calcination temperature and stability, leaching, and acidity were addressed for all studied catalysts. These data were correlated to the conversion and/or selectivity of the main product and were used for recovery of the catalysts. Moreover, it was clear that the strength of interaction of the heteropoly acid with the surface support as well as the acidity define the capacity of utilization of these catalysts. Effective ways to recovery the initial activity is still a challenge to take full advantage of these materials.

Neste trabalho, teve-se como objetivo a preparação de zeólitas básicas através da modifcação de zeólitas USY com bário e estrôncio e sua aplicação na reação de transesterifcação de óleo de soja com etanol, para produção de ésteres de etila (biodiesel). Além disso, foram estudados os efeitos da geração de sítios básicos na superfície dos catalisadores, bem como suas respectivas atividades por três ciclos catalíticos. O biodiesel obtido nos ciclos foi analisado por HPLC, CG-FID e espectroscopia Raman. Já os catalisadores foram caracterizados por FTIR, análises térmicas e adsorção gasosa de piridina e CO2. Soybean oil transesterifcation with ethanol was carried out in a batch reactor using USY zeolites modifed with barium and strontium (15 wt.%) as catalysts. A series of three catalytic cycles were performed for each zeolite without any loss of activity. The biodiesel product was analyzed by HPLC and FT-Raman, and the catalysts by pyridine and CO2 adsorption. Ba/USY provided higher conversions (> 97%) than Sr/USY (< 75%). The increased catalytic activity of Ba/USY was attributed to two different effects: a larger number of basic sites; and a lower interaction between barium species and HUSY Brønsted sites.

Determination of chlorine ions of pesticides was performed after dechlorination reaction using a palladium/magnesium system. Chlorine ions were quantified by potentiometry with ion-specific electrode. Rates of dechlorination of 100 microg of DDT as a function of reaction time and percent (wt/wt) of palladium deposited on the magnesium particles were determined. The best reaction conditions to DDT dechlorination were achieved with an acetone/water (1:1) solution and DDT reaction with a 0.27% (wt/wt) palladium/magnesium bimetallic system at room temperature for 10 min. The detection limit was of 0.24 microg/mL. This low cost method showed an efficiency of 92% in determining chlorine ions derived from DDT, it is fast, requiring no specialized laboratory equipment.

A method is presented for the choice of spectral regions when absorption measurements are coupled to chemometric tools to perform quantitative analyses. The method is based on the spectral distribution of the relative standard deviation of concentration (s c/c). It has been applied to the development of PLS-FTNIR calibration models for the determination of density and MON of gasoline, and ethanol content and density of ethanol fuel. The new method was also compared with the correlation (R²) method and has proved to generate PLS calibration models that present better accuracy and precision than those based on R².

Zeolite beta acidity, activated at 550 degrees C, was characterized by calorimetric and adsorption studies of pyridine in cyclohexane (Cal-Ad). Two different acid sites were found: n(1) = 0.1612 mmol g(-1) with DeltaH(1) = -83.6 kJ mol(-1); and n(2) = 0.3820 mmol g(-1) with DeltaH(2) = -62.8 kJ mol(-1). Step calcinations followed by FTIR indicated n(1) as Lewis sites and n(2) as weak Brønsted sites. When activated at 450 degrees C, zeolite beta showed three different sites: n(1) = 0.0467 mmol g(-1) with DeltaH(1) = -227.3 kJ mol(-1); n(2) = 0.1163 mmol g(-1) with DeltaH(2) = -93.3 kJ mol(-1); and n(3) = 0.3322 mmol g(-1) with DeltaH(3) = -80.4 kJ mol(-1). Sites n(1) and n(2) were assigned as Brønsted centers, while n(3) as a combination of Brønsted and Lewis sites. These results suggest that the zeolite beta strongest Brønsted sites are converted to Lewis sites at 550 degrees C. These Lewis sites are not only related to extra-framework Al species, but also to aluminium atoms partially bonded to the zeolite framework, as evidenced by infrared bands at 3777 and 875 cm(-1). FTIR and thermogravimetric analyses of gas phase adsorbed pyridine were also used to investigate the materials acidity and a good agreement was found with Cal-Ad data. The results showed that the Cal-Ad method offers a more detailed description of the zeolite surface acidity by providing thermodynamic parameters not easily obtained by other techniques. A linear relationship between enthalpy and entropy values for several zeolites (ZSM-5, TS-1, MOR, Y and BEA) is also reported.

Acid strength distribution measurements of zeolite Y by a combined analysis of calorimetric and adsorption data, Cal-ad, for the reaction of zeolite Y with pyridine, 2,6-lutidine, 2,6-di-tert-butylpyridine, quinoline, tetrahydrothiophene and benzonitrile show the presence of three families of acid sites. The strongest sites (heats above −29 kcal mol−1) contain a significant number of Bronsted sites (n = 0.1 mmol g−1), which are located inside the large cages. The sites of intermediary strength (heats around −17 kcal mol−1) are of Lewis and Bronsted types and the weaker sites (heats below −10 kcal mol−1) contain significant hydrogen bonding. The strength of these sites is probably due to mutual interaction between Lewis and Bronsted sites. The accessibility on zeolite and the size of the probe molecules play fundamental role on the determination of acid site distribution. Application of the electrostatic–covalent model (ECW) to this acid provides quantitative parameters for determination of donor-acceptor contributions based on electrostatic (EA) and covalent (CA) intrinsic characters to each chemical bonding. The results demonstrate that zeolite Y has a stronger covalent character with EA = 5.25, CA = 6.89 (CA/EA = 1.31) consistent with softness properties suggested in the literature.