Microcalorimetry spectroscopy

The microcalorimetry of NH3 adsorption coupled with infrared spectroscopy was used to study the effect of the synthesis medium (OH or F ) on the nature and amount of acid sites present in Al,Si-MFl zeolites [103]. Both techniques revealed that H-MFl (F ) with Si/Al < 30 contained extra-framework aluminum species. Such species were responsible for the presence of Lewis acid sites and poisoning of the Brpnsted acidity. In contrast, MFl (F ) characterized by Si/Al > 30 presented the same behavior as H-MFl (OH ). 

It was proven that microcalorimetry technique is quite well developed and very useful in providing information on the strength and distribution of acidic and basic sites of catalysts. When interpreting calorimetric data, caution needs to be exercised. In general, one must be careful to determine if the experiments are conducted under such conditions that equilibration between the probe molecules and the adsorption sites can be attained. By itself, calorimetry only provides heats of interaction. It does not provide any information about the molecular nature of the species involved. Therefore, other complementary techniques should be used to help interpreting the calorimetric data. For example, IR spectroscopy needs to be used to determine whether a basic probe molecule adsorbs on a Brpnsted or Lewis acid site. 

Some very important surface properties of solids can be properly characterized only by certain wet chemical techniques, some of which are currently under rapid improvement. Studies of adsorption from solution allow determination of the surface density of adsorbing sites, and the characterization of the surface forces involved (the energy of dispersion forces, the strength of acidic or basic sites and the surface density of coul-ombic charge). Adsorption studies can now be extended with some newer spectroscopic tools (Fourier-transform infra-red spectroscopy, laser Raman spectroscopy, and solid NMR spectroscopy), as well as convenient modern versions of older techniques (Doppler electrophoresis, flow microcalorimetry, and automated ellipsometry). 

In a more detailed study Caturla et al. [112] investigated the interaction of four catechins with PC and PE model membranes by fluorescence spectroscopy, microcalorimetry, and infrared spectroscopy. DPH fluorescence anisotropy was monitored as a function of temperature and it was observed that catechins either did not change or increased DPH anisotropy. The membrane rigidifying effect of (-)-epicatechin (EC) (37b) was the most... 

Mourtzis, N. Cordoyiannis, G. Nounesis, G. and Yannakopoulou, K. (2003) Single and Double Threading of Congo Red into y-Cyclodextrin. Solution Structures and Thermodynamic Parameters of 1 1 and 2 2 Adducts, as Obtained from NMR Spectroscopy and Microcalorimetry, Supramol. Chem. 15, 639-649. 

When silica with the developed specific surface (> 100m2/g) is used, the number of active sites per gram of material reaches 1018-1019. This amount is sufficient for their reliable detection by different methods EPR, IR and optical spectroscopy, microcalorimetry, and adsorption measurements. Using the thermo chemical method, one can activate the surface of powdered and semitransparent film Si02 samples with a thickness of several tens of microns obtained by pressing the high-dispersity silica powder (aerosil). These film samples are suitable for quantitative optical studies in the UV, visible, and IR regions. 

The combined use of adsorption microcalorimetry and IR spectroscopy allows a precise evaluation of the hydrophilic or hydrophobic character of the silica powders investigated.10"12 The evolution of the enthalpy of adsorption of water with coverage (Figure 1) indicates the coverage values at which the enthalpy falls below the latent enthalpy of liquefaction which can be taken as a... 

Much of the early studies of surfactant adsorption at the solid-solution interface were based on classical experimental techniques, such as solution depletion [1, 32], fluorescence spectroscopy [2], and measurements of the differential enthalpy of adsorption [2], Such methods have provided much of the basic initial understanding. However, they provide no direct structural information and are difficult to apply to mixtures [23, 34], However, when combined with other techniques, such as NMR and flow microcalorimetry, they provide some insight into the behaviour of mixtures. This was demonstrated by Thibaut et al. [33] on SDS/C10E5 mixtures adsorbed onto silica and by Colombie et al. [34] on the adsorption of SLS/Triton X-405 mixtures onto polystyrene particles. 

Several methods have been used to determine the surface acidity of solid acids, but each method has its limitations. Common methods are titration with the Hammett indicators, temperature-programmed desorption (TPD), adsorption microcalorimetry, catalytic test reactions, and IR and NMR spectroscopies. These techniques exhibit several advantages and disadvantages. 

The effect of adsorption temperature on metals or supported metals on the mobility of adsorbed probe molecules has not received as much attention as on metal oxides. Gelin and co-workers (96) used adsorption microcalorimetry at 296 and 423 K and IR spectroscopy to study the adsorption of CO on Ir supported on NaY zeolite reduced from 383 to 923 K and on Ir supported on silica. At 296 K it was observed that for intermediate coverages (6 > 0.3) the kinetics of adsorption changed, with the thermograms displaying long tails... 

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