Vibrational and thermodynamic properties of Ar, N2, O2, H2 and CO adsorbed and condensed into (H,Na)-Y zeolite cages as studied by variable temperature IR spectroscopy

Abstract

The adsorption of Ar, H2, O2, N2 and CO on (H,Na)-Y zeolite (Si/Al = 2.9, H+/Na+ approximately 5) has been studied at variable-temperature (90-20 K) and sub-atmospheric pressure (0-40 mbar) by FTIR spectroscopy. Unprecedented filling conditions of the zeolite cavities were attained, which allowed the investigation of very weakly adsorbed species and of condensed, liquid-like or solid-like, phases. Two pressure regimes were singled out, characterized by: (i) specific interaction at low pressure of the probe molecules (P) with the internal Brønsted and Lewis sites, and (ii) multilayer adsorption at higher pressure. In the case of CO the perturbation of the protonic sites located inside the sodalite cages was also observed. As the molecule is too large to penetrate the sodalite cage, the perturbation is thought to involve a proton jump tunneling mechanism. The adsorption energy for the (HF)OH...P (P = Ar, H2, O2, N2 and CO) specific interaction involving the high frequency Brønsted acid sites exposed in the supercages was derived following the VTIR (variable temperature infrared spectroscopy) method described by E. Garrone and C. Otero Areán (Chem. Soc. Rev., 2005, 34, 846).

Ab Initio Simulation of the Acid Sites at the External Surface of Zeolite Beta

“…Al−(H 2 O) exhibits slightly lower frequency shifts than bridging OH groups (calculated values: 31–34 cm −1 ), which is also compatible with the experimental band at =2175 cm −1 and possibly also with that at =2165 cm −1 (shift: 22 cm −1 ) usually assigned to Al−OH groups . With regard to Al−OH groups, we calculate much lower frequency shift values (8–13 cm −1 ), which could perhaps correspond to the experimental band at =2160 cm −1 (shift: 16 cm −1 ), usually assigned to weak BAS, such as Si−OH groups . For the Si−OH groups, we found intermediate frequency shifts (25–30 cm −1 , in line with previous findings from Bucko et al.…”

“…Conversely, Al−(H 2 O) sites at the external surface exhibit similar adsorption energies (−24 to −42 kJ mol −1 ) to bridging OH groups within bulk Beta. Consequently, the value of approximately −30 kJ mol −1 measured experimentally and assigned usually to bulk bridging OH groups in zeolites is also compatible with Al−(H 2 O) groups at the external surface. Notably, upon CO adsorption, Al−(H 2 O) species were invoked experimentally to be BAS on Al‐MCM41 samples …”

Probing zeolites by vibrational spectroscopies

“…17,154,[274][275][276][277][278][279][280][281][283][284][285]288, In brief, the technique is based on displacement of the equilibrium between molecules in the gas phase and those adsorbed on a given type of surface site, which is carried out by changing the temperature T of the system, as shown in Fig. 17,154,[274][275][276][277][278][279][280][281][283][284][285]288, In brief, the technique is based on displacement of the equilibrium between molecules in the gas phase and those adsorbed on a given type of surface site, which is carried out by changing the temperature T of the system, as shown in Fig.…”

“…From eqn (30), it emerges that by changing from p 0 to p 0 0 the left-hand side of eqn (30) will change by a constant value of ln( p 0 /p 0 0 ). 736 154 investigated the adsorption of Ar, H 2 , O 2 , N 2 and CO on H-Na-Y zeolite (Si/Al = 2.9; H + /Na + = 5) by means of VTIR in the temperature range of 90-20 K and pressure range of 0-40 mbar. Conversely, it will change the intercept with the ordinate axis and thus the extrapolated DS1 value by a factor of R ln(p 0 /p 0 0 ).…”

Atomic scale characterization and surface chemistry of metal modified titanate nanotubes and nanowires

“…The presence of a shoulder at 2178 cm À 1 is due to Na þ …CO complexes formed on residual Na þ ions [301]. With regard to the weak shoulder at 2130-2135 cm…”