Molar Entropy and Enthalpy of CO Adsorbed in Zeolites as Derived from VTIR Data: Role of Intermolecular Modes

Detailed analysis of recently reported variable-temperature IR (VTIR) spectra of carbon monoxide adsorbed in alkaline zeolites shows how, not only the corresponding values of standard adsorption enthalpy ((Formula presented.)) and entropy ((Formula presented.)) can be obtained, but also the thermodynamic values of molar entropy and enthalpy which characterize the adsorbed gas phase. In addition, it is shown that the so obtained molar entropy data can lead to new insights into soft molecular modes, which would be hardly accessible by conventional IR spectroscopic techniques

Variable temperature infrared spectroscopy: a convenient tool for studying the thermodynamics of weak solid-gas interactions

This tutorial review describes the use of variable temperature infrared spectroscopy of adsorbed species (VTIR), a recent method for studying the thermodynamics of weak solid-gas interactions. Examples show how a fundamental relationship of thermodynamics (the van't Hoff equation, used long since in several fields of physical chemistry) can describe equilibrium processes at the solid-gas interface. The VTIR method is fully exploited by measuring absorbance of an IR band, temperature and pressure over a wide temperature range: an estimation of the interaction energy is, however, possible even ignoring the equilibrium pressure. Precise thermodynamic characterization of solid-gas interactions is required in several fields: on the applied side, gas sensing, separation and storage, which involve such areas as work-place security, air pollution control and the energy sector; regarding fundamental knowledge, weak solid-gas interactions are relevant to a number of fields, including hydrogen bonding, coordination chemistry and surface phenomena in a broad sense. Infrared (IR) spectroscopy of (gas) molecules adsorbed on a solid is frequently used to characterize both, the adsorbed species and the adsorbing centres at the solid surface. The potential of the technique can be greatly enhanced by obtaining IR spectra over a temperature range, and simultaneously measuring IR absorbance, temperature and equilibrium pressure. When this is done, variable temperature infrared (VTIR) spectroscopy can be used not only for a more detailed surface characterization, but also for precise studies on the thermodynamics of solid-gas interactions. Furthermore, when weak interactions are concerned, the technique shows favourable features compared to adsorption calorimetry, or to other classical methods. The potential of the VTIR method is highlighted by reviewing recently reported studies on dihydrogen, dinitrogen and carbon monoxide adsorption on zeolites. To facilitate understanding, an outline of the basis of the method is also given, together with an appraisal of the critical points involved in its practical use

Effect of Calcination on the Structure and Texture of Gamma-Alumina Prepared by Thermolysis of Aluminium Sulphate

Thermal decomposition of aluminium sulphate at 1173 K produces mesoporous γ-alumina with a BET surface area of 134 m 2 g −1 . This active alumina was subsequently calcined in air at temperatures ranging from 1173 to 1523 K. The microcrystalline structure, surface area and porous texture of the resulting materials were analysed by X-ray diffraction and nitrogen adsorption measurements. The results suggest that γ-alumina is converted into the α-modification in the sequence: γ-alumina → δ-alumina → θ-alumina → α-alumina. All oxides calcined within the temperature range 1173–1473 K were found to be mesoporous. The most frequent pore radius increased slowly, from 10.5 to 13.5 nm, as the temperature was raised from 1173 to 1423 K. However, calcination at 1473 K resulted in a sharp increase of pore radius (up to 18.5 nm) with simultaneous reduction of the BET surface area and total pore volume by over 75%. The sample fired at 1523 K showed a BET surface area smaller than 5 m 2 g −1