Calorimeters Can be Applied for the Characterization of Solid Materials

If pollutants abatement is performed using solid adsorbent or catalysts, the characterization of these substances is necessary. For that purpose, numerous methods have to be used those enabling information about structure the others that provide data concerning texture and those that reveal the existence of active sites for adsorption (conversion) of particular pollutants. Evidently, multi-technique approach has to be applied in order to perform full characterization of materials applied for pollutants abatement. Among the other techniques, calorimetry may be applied for the charac- 

It is important to point out that acidic/basic character may be decisive for the reactivity of a solid material in the reactions important for pollutants abatement. The data concerning acidity/basicity can be obtained using several methods, such as IR, XPS and Raman spectroscopies temperature-programmed desorption, and calorimetry. Among them, calorimetry gives multi-indicative data the adsorption of successive injections (doses) of so-called probe molecules happens onto the sample s surface while it is kept at a constant temperature and a heat-flow detector notice the amount of heat transferred per time. 

An experiment of adsorption from the gas-phase, performed in microcalorimeter coupled with volumetric line can give a profile of Qdi/ versus the amount adsorbed, integral heats of adsorption, adsorption isotherms (adsorbed amounts vs. equilibrium pressure) and irreversibly absorbed amount of a chemisorbed gas the same stands for the adsorption from the liquid-phase, where the adsorbate (titrant) is added to both sample and reference ceUs simultaneously. The profile of differential heats versus the uptake of probe gives the data concCTning the amount, strength and distribution of the active sites. Besides, the values of initial heats of adsorption characterize the strongest sites active in adsorption process. For the sake of acidic/basic characterization of solids surface, the most commonly used gas-phase probes are ammonia, pyridine or some amines for the interaction with acidic sites. SO2 and CO2 are the probes used to notice and characterize the basic sites. In microporous solids, the accessibility of active sites is not the same for the molecules of different sizes. Therefore, many different probes can be applied to study acidity or basicity of same solid materials this approach brings additional information. For example, acidity of zeolites can be characterized by adsorption of ammonia, but also by adsorption of pyridine (from the gas phase) and aniline (from the liquid phase) [20-22], Liquid microcalorimetry can be also used for the determination of acidic character of solid adsorbent the common liquid-phase probe is aniline dissolved in n-decane [40]. 

The obtained information about the acidic/basic character can be correlated with the adsorption possibilities. The possibility of some solid material to adsorb (or modify) the atmospheric or water pollutant depends very often on these features. Therefore, there are literature sources that report the correlations between acidity/basicity of different materials and their abilities in pollutants abatement. For example, balanced acidic/basic properties are indispensable for an efficient conversion of NOx, that is, high activity and selectivity, over a broad temperature range. In case of alumina-supported indium oxide catalysts, microcalorimetry of ammonia and SO2adsorption helped to find effective formulations [41], 

Finally, it can be summarized that, in the domain of environment protection microcalorimetry gives possibilities to  

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