Hydrogen storage in Chabazite zeolite frameworks

Abstract

We have recently highlighted that H-SSZ-13, a highly siliceous zeolite (Si/Al = 11.6) with a chabazitic framework, is the most efficient zeolitic material for hydrogen storage [A. Zecchina, S. Bordiga, J. G. Vitillo, G. Ricchiardi, C. Lamberti, G. Spoto, M. Bjørgen and K. P. Lillerud, J. Am. Chem. Soc., 2005, 127, 6361]. The aim of this new study is thus to clarify both the role played by the acidic strength and by the density of the polarizing centers hosted in the same framework topology in the increase of the adsorptive capabilities of the chabazitic materials towards H2. To achieve this goal, the volumetric experiments of H2 uptake (performed at 77 K) and the transmission IR experiment of H2 adsorption at 15 K have been performed on H-SSZ-13, H-SAPO-34 (the isostructural silico-aluminophosphate material with the same Brønsted site density) and H-CHA (the standard chabazite zeolite: Si/Al = 2.1) materials. We have found that a H2 uptake improvement has been obtained by increasing the acidic strength of the Brønsted sites (moving from H-SAPO-34 to H-SSZ-13). Conversely, the important increase of the Brønsted sites density (moving from H-SSZ-13 to H-CHA) has played a negative role. This unexpected behavior has been explained as follows. The additional Brønsted sites are in mutual interaction via H-bonds inside the small cages of the chabazitic framework and for most of them the energetic cost needed to displace the adjacent OH ligand is higher than the adsorption enthalpy of the OH...H2 adduct. From our work it can be concluded that proton exchanged chabazitic frameworks represent, among zeolites, the most efficient materials for hydrogen storage. We have shown that a proper balance between available space (volume accessible to hydrogen), high contact surface, and specific interaction with strong and isolated polarizing centers are the necessary characteristics requested to design better materials for molecular H2 storage.

New frontier in transmission IR spectroscopy of molecules adsorbed on high surface area solids: Experiments below liquid nitrogen temperature

“…9c), the 4130 cm À1 band is assigned to Si-OHÁ Á ÁH 2 adducts formed at the surface of the zeolite crystals. A parallel experiment with the isostructural H-SAPO-34 (not reported here for brevity), has shown very similar results confirming the present assignment [91].…”

“…The potentialities of monitoring by means of FT-IR spectroscopy the adsorption of probe molecules at temperature lower than liquid nitrogen have been recently extended also to microporous systems, such as zeolites and MOFs [30,50,51,91]. As an example, we report here the recent results obtained on a Cu + exchanged ZSM-5 zeolite, by following the evolution of Cu + (H 2 ) adducts as a function of H 2 pressure and temperature.…”

Hydrogen adsorption in a copper ZSM5 zeoliteAn inelastic neutron scattering study

“…Zeolites are potential hydrogen storage materials [2][3][4][5][6][7]. The uptake of dihydrogen by zeolites can be mediated by specific interactions due to particular components of the zeolite.…”

Zeolites and Other Structurally Microporous Solids as Acid–Base Materials

“…The chabazite structure contains only one tetrahedral site but four different oxygen atoms in the asymmetric unit, giving four possible acid-site configurations, depending on to which of the oxygen atoms the proton is attached. 212,213 After activation, SAPO-34 gives five IR peaks in the range of 3000e4000 cm À1 representing five types of hydroxyl groups. Two peaks at 3625e3628 and 3598e3605 cm À1 can be attributed to two types of Si(OH)Al groups.…”