Microcalorimetry experiments

The influence of the nature of the aluminum source on the acidic properties of mesostructured materials (MCM41) has also been studied in the literature [244]. Microcalorimetry experiments using ammonia as a probe molecule have shown that Al insertion into the mesoporous silicate framework affected acid site strength and distribution in a manner controlled by the synthesis conditions (materials prepared... 

Microcalorimetry experiments with NH3 and pyridine as probe molecules indicated that insertion of Ga into the offretite aluminosilicate structure increased the overall acid sites strength of the crystals while decreasing its acid sites density [255], The observed heterogeneity of acid site strength distribution of H,Ga,Al-offretites was attributed to some extra-framework Al(Vl) and Ga(Vl) species generated during the ion exchange and calcination procedures used to prepare H-offretite crystals. 

Unfortunately microcalorimetry experiments for the heat of wetting are difficult to perform due to the care that must be taken to keep the powder surface free from adsorbed impvuities. As a result an approximate method based on an infrared band shift caused by the interaction of the solvent with the solid surface has been developed. Drago often used spectroscopic shifts,, of the OH stretching frequency of phe-... 

Microcalorimetry is used to monitor thermal changes associated with physical and/or chemical events that do not require heating or cooling for their initiation. Such events include dissolution, precipitation, reaction, and crystallization. In a typical microcalorimetry experiment, these events are triggered in a controlled manner by mixing two preequilibrated and... 

A prior study of the adsorption of nitrogen at 77 K on 5A and 13X zeolites using quasiequilibrium, isothermal, adsorption microcalorimetry experiments at 77K [16] has detected a step in the differential enthalpies of adsorption, towards the end of micropore filling. At the time, this was interpreted as a consequence either of the adsorbate-adsorbate interactions, or... 

Typical output from differential titration microcalorimetry experiments (binding of various polysaccharides to CBM 35 reproduced by kind permission of Prof. H. J. Gilbert). The top traces are the rates of heat change, the bottom their integrals. 

The binding parameters of both hosts with chloride were determined using isothermal titration calorimetry. The microcalorimetry experiments re-... 

Ramsahye NA, Maurin G, Bourrelly S (2007) On the breathing effect of a metal-organic framework upon CO2 adsorption monte carlo comptu-ed to microcalorimetry experiments. Chem Commun 31 3261-3263... 

Rotenberg, B., J.-P. Morel, V. Marry, P. Turq, and N. Morel-Desrosiers. 2009. On the driving force of cation exchange in clays Insights from combined microcalorimetry experiments and molecular simulation. Geochimica et Cosmochimica Acta Ti, no. 14 4034-4044. doi 10.1016/j.gca.2009.04.012. 

Toluene and water adsorption microcalorimetry experiments have shown the strictly hydrophobic nature of pure Si02 zeolite Beta synthesized in F" medium, while evidencing a slight increase in the hydrophilicity of the materials upon incorporation of Ti into the framework. This was found to be due to the relatively strong adsorption of precisely one H2O molecule per Ti site. In contrast, materials synthesized in OH medium showed an enhanced hydrophilicity [254]. 

Results obtained by temperature-programmed desorption suggested that in the case of bimetallic catalysts there was a reduction in the number of strong CO-adsorption sites. This finding allows conclusion that the alloying effect of these systems leads to the lowering of the CO heat of adsorption. This finding was confirmed by direct measurement of differential heat of CO chemisorption in the microcalorimetry experiment (see Fig. 4.20). 

Mitani at al., in their work related to the investigation on the acidity of faujasites with different framework aluminium content, reported that the extent of the decrease in acid sites concentration varies with the kind of basic probe used in microcalorimetry experiments (see Fig. 9.6) [92]. The experimental results were explained by differences in molecular diameters of ammonia and pyridine, and the fact that pore size of zeolite becomes widely distributed as the dealumination proceeds so OH groups in supercages have become available for adsorption of such large molecule as pyridine is. 

In a study performed by Auroux et. al. [Ill] microcalorimetry experiments of ammonia and sulfur dioxide were performed in order to analyze the possible correlations between the acidity and basicity of the alkali-metal ion-exchanged X and Y zeolite structures and their catalytic properties. The catalytic results for the 4-methylpentan-2-ol conversion show that activity and selectivity are both affected to some extent by the acid-base character of the catalysts. The activity was found to increase in order Cs > Rb > K > Na > Li for both X and Y zeolites. The dehydrogenation reaction occurs only on CsX + CS2O, which presents very strong basicity. The product selectivity of the reaction depends on both Lewis acidity and basicity Lewis basic or acidic sites of zeolites can be considered as acid-base pairs, in which both framework basic oxygens and neighboring cations are important. The selectivity ratio between the 1-alkene and (2-alkene+isomers) increases linearly with the ratio between basic and acid sites number, so2/ nh3, for both X and Y zeolites, as shown in Fig. 9.14. 

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