Role of extraframework metal sites for hydrogen adsorption into the pores of a zeolite: FT-IR study
✍ Scribed by Olena Zavorotynska; Jenny G. Vitillo; Giuseppe Spoto; Adriano Zecchina
- Publisher
- Elsevier Science
- Year
- 2011
- Tongue
- English
- Weight
- 543 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0360-3199
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✦ Synopsis
In order to compare the adsorptive properties of nanoporous zeolites containing extraframework cations of different nature, we have studied the interaction of H 2 with Na-A, Ca-A, and Co,Na-A zeolites. Low temperature Fourier transform infrared (FT-IR) spectroscopy was used for the investigation, as this technique is highly sensitive and responsive to the nature of the gas/surface interaction and can in addition allow for the estimation of the adsorption enthalpy. In all cases the spectra of adsorbed H 2 have complex structure due to ortho/para splitting as well as to surface structural disorder. Na þ and divalent Ca 2þ were found to induce almost similar perturbation on H 2 molecule, resulting in the shift of the HeH vibrational frequency of À86 cm À1 and À76 cm À1 respectively (as compared to the Raman frequency of gaseous H 2 ). The enthalpy of adsorption, estimated by the Variable Temperature Infrared (VTIR) method, is À13 AE 1 kJ mol À1 for the strongest adsorptive sites in Na-A and Ca-A samples. In the case of Co,Na-A the shift of the HeH frequency due to the formation of H 2 /Co 2þ complexes is larger (ca. À180 cm À1 ) suggesting that the interaction can involve some, although small, chemical contribution.