Quantitative FTIR studies of hexagonal and cubic faujasites by pyridine and CO adsorption - Numbers and relative acidity of the HF and LF zeolitic hydroxy groups

Some properties of hexagonal and cubic, highly crystalline faujasites are compared by means of two sorbed probes (pyridine and CO) studied by FTIR spectroscopy. Whatever the structural variety, the acid strength of the HF and LF hydroxy groups and the (LF)OH contribution to the pyH(+) species increase with the Si/Al-F ratio. A nu(CO/LF) band detectable between 2160 and 2167 cm(-1) is assigned to the formation of the (LF)OH ... CO complex, its wavenumber value depends on the dealumination and coverage levels. The molar absorption coefficients, epsilon, of the HF and LF bands of HEMT zeolite are similar to those of HF and LF bands of HY zeolite, respectively. No structural effect is detectable. The progressive CO adsorption confirms the epsilon(HF) value previously determined by pyridine adsorption, and the results obtained for epsilon(LF) are discussed.