#Molar entropy free

Throughout the text, the zeolite adsorption site will be considered to remain fixed, and all changes will be attributed to the adsorbed molecule alone. From here onwards, the Z representing the zeolite framework will be dropped for simplicity.

Where Zв€’M + stands for the adsorption site and Zв€’M +в‹…в‹…в‹…CO is the adsorption complex. Referring to CO adsorption on singleвЂђcation adsorption sites of alkaline zeolites, let Eq.вЂ…(1) below represent the adsorption equilibrium: Herein, an extension of those studies to include determination of the molar enthalpy and entropy of the adsorbed gas is proposed and discussed.ДЄn outline of the VTIR spectroscopic method is reported below. Over the years, several cases have been studied, so that some more general considerations are now possible. 16, 17 As briefly reported below, application of basic thermodynamics to a set of VTIR data gives access to the fundamental quantities for the (Langmuirian) adsorption process, i.вЂ‰e. This procedure has been termed VTIR (VariableвЂђTemperature IR) spectroscopy.

14, 15 However, for Langmuir type adsorption, a method has been designed in the recent past, envisaging the recording of IR spectra of an adsorbed species at different temperatures, while simultaneously measuring the temperature and equilibrium pressure. 13 For such a purpose, classical infrared spectroscopy (IR) can give valuable structural information, derived from analysis of the wavenumber shifts undergone by vibrational modes of the adsorbed molecule but determination of the gasвЂђsolid interaction energy is out of reach, unless some other complementary technique is also used.

12Д¬rystallinity of their aluminosilicate framework and regular layout of their internal channels (and cages) endow zeolites with a regular distribution of charge balancing cations, which can form arrays of all equal and nonвЂђmutuallyвЂђinteracting adsorption sites, thus facilitating the use of the Langmuir model for studying gas adsorption thermodynamics. Possible redox processes that can take place when the adsorbents show exposed transition metal ions ( e.вЂ‰g., supported NiO). The formation of a small proportion of isocarbonyl species, which show the CO molecule interacting through the oxygen atom with the cation (M +в‹…в‹…в‹…OC) 11 The simultaneous interaction of the probe molecule with two neighboring cationic centers, observed sometimes when dealing with zeolites that have a small SiвЂ‰:вЂ‰Al ratio 9, 10

#Molar entropy free

1, 2, 3, 4, 5, 6, 7, 8 A main reason to choose CO for that purpose comes from the fact that, when used at a small dose, the main gasвЂ“solid interaction process taking place is the coordination of CO (through the C atom) to a single cation, thus forming a monocarbonyl (M +в‹…в‹…в‹…CO) species, which can easily be monitored by the corresponding hypsochromic shift of the Cв€’O stretching mode, from the 2143вЂ…cm в€’1 value shown in the free gas phase. Carbon monoxide is a probe molecule very often used to investigate cationic adsorption sites in zeolites (and metal oxides) by infrared spectroscopy.