Microcalorimetric techniques

Malaspina, L., Bardi, G., Gigli, R. (1974) Simultaneous determination by Knudsen-effusion microcalorimetric technique of the vapor pressure and enthalpy of vaporization of pyrene and 1,3,5-triphenylbenzene. J. Chem. Thermodyn. 6, 1053-1064. 

Nickel oxide, prepared by dehydration of nickel hydroxide under vacuum at 250°C. [NiO(250)]y presents a greater activity in the room-temperature oxidation of carbon monoxide than nickel oxide prepared according to the same procedure at 200° C. [NiO(200)]> although the electrical properties of both oxides are identical. The reaction mechanism was investigated by a microcalorimetric technique. On NiO(200) the slowest step of the mechanism is CO. i(ads) + CO(ads) + Ni3+ 2 C02(g) + Ni2+, whereas on NiO(250) the rate-determining step is O (0ds) + CO(ads) + Ni3+ - C02(g) + Ni2+. These reaction mechanisms on NiO(200) and NiO(250), which explain the differences in catalytic activity, are correlated with local surface defects whose nature and concentration vary with the nature of the catalyst. 

The influence of the surface structure upon the catalytic activity is likely to be particularly important in the case of finely divided nickel oxides, prepared at a moderate temperature, which present catalytic activity for this reaction at room temperature. In a previous work, we studied the room-temperature oxidation of carbon monoxide on nickel oxide prepared by dehydration of the hydroxide under vacuum (p = 10"6 torr) at 200°C., by means of a microcalorimetric technique (8, 20). The object of this work is to re-investigate, by the same method, the mechanism of the same reaction on a nickel oxide prepared at 250°C. [NiO(250)] instead of 200°C. [NiO(200)]. 

We have recently developed a microcalorimetric technique for quantifying the energetic changes of microorganisms colonizing a sea-water-sediment interface in experimental microcosms. The inherent low specificity of direct microcalorimetry and, moreover, the high sensitivity and reliability of modern microcalorimeters proved advantageous, since unknown and subtle events, not shown by more specific methods, may be detected. 

A considerable amount of fundamental physiological research on striated muscle has been done with the aid of calorimetiy in the last 80 years but, only recently has the heat dissipation in human tissue been used as an indicator of clinical conditions. Monti s group has successfully developed a microcalorimetric technique for studying the metabolic activity of biopsies from the vastus lateralis... 

In principle, to carry out immersion microcalorimetry, one simply needs a powder, a liquid and a microcalorimeter. Nevertheless, it was early realized that the heat effects involved are small and the sources of errors and uncertainties numerous. Many attempts have been made to improve immersion microcalorimetric techniques. Before commenting on this type of experiment, we describe the equipment and procedure which has been found by Rouquerol and co-workers to be of particular value for energy of immersion measurements (Partyka et al., 1979). 

As we have already seen, it is not difficult to undertake accurate energy of immersion measurements provided that the microcalorimetric technique is carefully selected and that certain precautions are taken. It was pointed out by Chessick (1962) that it is deceptively easy to obtain heat of wetting data, but the results will be of very little scientific value unless steps are taken to ensure that the adsorbent and the liquid have been properly prepared and that the conditions of the experiment meet well-defined thermodynamic requirements. 

Adsorption microcalorimetry is probably the most direct method for describing in detail both the quantitative and the energetic features of surface sites. The ability of the microcalorimetric technique to readily reveal subtle differences among samples is worth stressing. Even though one has to be cautious about the nature of the acidic and basic sites, calorimetric information on the concentration and strength of the sites can be used with confidence for interpreting the catalytic behavior. 

Complex-formation has been shown to occur between some methyl glycosides and Na, Ca, and La ions by a microcalorimetric technique, and the enthalpies of interaction have bran determined. This method also gives information on the stoichiometry of the complex. Osmotic coeflS-cients, determined by the isopiestic comparison mediod, of systems containing an electrolyte and a non-electrolyte have bran shown to offer simple and sensitive means for the study of weak complexing interactions in aqueous solution. ... 

The microcalorimetric technique is employed in the present investigation to study the acidity patterns of the different TS-1 samples prepared according to the conventional and sol-gel methods. The influence of the Ti content in framework and effect of method of preparation on the number and strength of acid sites form the content of the paper. 

Using infrared and microcalorimetric techniques led Vedrine et al. to propose that phosphorus neutralizes medium and strong acid sites at the entrance of the zeolite channels. The strongest acid sites, however, would not be modified. As a result, the activity of the modified catalyst was comparable to that of the parent ZSM-5. The increased olefin selectivity was then assigned to the increased... 

Phillips and co-workers employed microcalorimetric techniques in complementing standard methods in the study of water adsorption [313] on chemically modified carbons with the high surlace areas. They found three distinct mechanisms of water adsorption on carbons and a strong dependence on surfece chemistry. Carbons treated with N2 at high temperatures chemically adsorbed water at unsaturated sites, while carbons treated in Hi adsorbed smalls amounts of water. Oxygenation of basic carbons increased the eapacity for water adsorption attributable to physical adsorption. 

The microcalorimetric technique has also been applied to investigate the adsorption of acetonitrile, dimethylether, water, pyrrole and ammonia on ferrierite, a small-pore zeolite [58], This investigation showed that the results of the determination of the site-strength distribution are dependent on the basic strength of the probe, on the acidity and porosity of the acid solid, and on the adsorption temperature. A similar calorimetric investigation of the acidity of de-aluminated Y-type zeolites was performed using the same probes [59],... 

Quantification of microbial PHA using GC method is rapid, sensitive, reproducible, and requires only small amount of samples (5-10 mg) for the analysis. Other techniques of analysis such as IR spectrometry at 5.75 A (Juttner et al. 1975), two-dimensional fluorescence spectroscopy, flow cytometry (Degelau et al. 1995) HPLC (Karr et al. 1983), ionic chromatography, and enzymatic determination (Hesselmann et al. 1999) were also desalbed. For online determination of PHA content in recombinant E. coli system, Fourier transform mid-infrared spectrometry (FTIR) and microcalorimetric technique (Ruan et al. 2007 Jarute et al. 2004) were also reported. For precise composition determination and structural elucidation of PHA, a variety of nuclear magnetic resonance (NMR) spectroscopy techniques have also been applied and the most commonly used are proton ( H) and carbon-13 ( C) NMR (Doi et al. 1986 Jacob et al. 1986). 

A. Auroux, R. Monad, E. Rombi, V. Solinas, A. Sorrentino, E. Santacesaiia, Acid sites investigation of simple and mixed oxides by TPD and microcalorimetric techniques. Thermochim. Acta. 379, 227-231 (2001). doi 10.1016/80040-6031(01)00620-7... 

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