FT-IR Studies of Interaction between Zeolitic Hydroxyl Groups and Small Molecules. 2. Adsorption of Oxygen, Hydrogen, and Rare Gases on H-Mordenite at Low Temperatures

FT-IR Studies of the Interaction between Zeolitic Hydroxyl Groups and Small Molecules. 3. Adsorption of Oxygen, Argon, Nitrogen, and Xenon on H−ZSM-5 at Low Temperatures

“…Difference spectra shown in Figure 3b clearly show the features; the differential shape of the silanol band indicates the slight upward shift of the band, and the growth of a new broad band at 3589 cm -1 at the expense of the 3621-cm -1 band is clearly seen. This feature is very similar to that observed for the O 2 adsorption on H-MOR at 110 K. 4 Hence, in accordance with the case of H-MOR, we interpret the observed change in the ν(OH) bands as the result of the formation of a 1:1 H-bonded complex between an acidic OH group and an O 2 molecule. The integrated absorbance of the negative band (3621 cm -1 in Figure 3b) and that of the positive one (3589 cm -1 ) had a linear correlation with that of the ν-(OO) band at 1550 cm -1 , confirming the formation of the 1:1 H-bonded complex.…”

“…A band with a fwhm (full width at half-maximum) of 4.5 cm -1 was observed at 1550 cm -1 , which was 6 cm -1 lower than that of a free molecule (1556 cm -1 ; Raman data). 16,17 Its peak position was almost the same as that of the ν(OO) band of the O 2 species adsorbed on the Brønsted acid sites (BAS) of H-MOR at 110 K. 4 The growth of the 1550-cm -1 band coincides with the change of the ν(OH) bands as described below. Hence the 1550-cm -1 band is assigned to the ν(OO) band of the O 2 species molecularly adsorbed on the BAS of H-ZSM-5.…”

“…This upward shift might be caused by either the lowering of the sample temperature brought about by the presence of the gas-phase component that acts as a heat carrier or the collision effect, as discussed previously. 4 This result suggests that the interaction of the silanol groups with O 2 is very weak in the pressure range, as is the case of H-MOR. 4 In contrast to that, the acidic-OH band at 3621 cm -1 was strongly perturbed with the increase in the O 2 pressure: the band decreased in intensity, and a new broad band grew at 3589 cm -1 .…”

“…4 This result suggests that the interaction of the silanol groups with O 2 is very weak in the pressure range, as is the case of H-MOR. 4 In contrast to that, the acidic-OH band at 3621 cm -1 was strongly perturbed with the increase in the O 2 pressure: the band decreased in intensity, and a new broad band grew at 3589 cm -1 . The fwhm (61 cm -1 ) of the new band was much larger than that of the acidic-OH band (28 cm -1 fwhm).…”

Molecular orbital model of the influence of interaction between O2 and aluminosilicate sites on the triplet–singlet energy gap and reactivity

“…Experimental techniques and theoretical methods have been used to study the interactions of oxygen molecule [19][20][21][22]. Several reports of fundamental absorption data of O 2 in cation exchanged zeolites [22][23][24][25] and in H-form zeolites [26,27] have been published. Oxygen sorption on the pores of HY, H-ZSM-5 and H-MOR has been studied by FT-IR and used to determine which Brønsted acid sites are accessible to oxygen molecule [26,28,29].…”