Structure and properties of acid sites in a mixed-oxide system. I. Synthesis and infrared characterization

Nature and Estimation of Functional Groups on Solid Surfaces

“…Similar OH stretching frequencies have been observed for BOH [131][132][133][134][135] and POH [134,136] groups on modified silica surfaces. In a study of "alumina-on-silica" a single bandof ::: SiOH was detected at 3744 cm-1 after heat treatment at 773 K [137]. The failure to detect any A10H bands was assumed to be due to the low Al concentration and mutual interactions of AIOH groups with other hydroxyl groups.…”

“…Attempts have been made to evaluate this ratio for pyridine normal modes, using the 19b mode, which occurs near 1450 cm -1 for coordinated pyridine species and near 1545 cm -1 for the pyridinium ion [137,217,[220][221][222]. The most reliable value is probably that given by Hughes and White [221] e (1450) e (1545) = 1.08 ± 0.09 (4) This value was recently verified by Matulewicz et al [217] who found a ratio of 0.9 ± 0.1.…”

Surface Acidities of Bentonite, Sepiolite, and Synthetic Silica-Aluminas

“…On the other hand, Siral 40, Siral 80, Sepiolite and Bentonite were given in Figures 4-7, respectively. The pyridine bands used in the evaluation of the data in the FTIR spectroscopic examination of pyridine adsorption from the gas phase on solid samples are given in Table 3 (14,15). All spectra (Figures 1-7) were evaluated according to this chart.…”

“…In the determination of the surface acidity of the catalysts, Hammett indicators (5)(6)(7)(8), amine titration (9), calorimetric method (10)(11)(12) and investigation of the gas phase adsorption of bases such as pyridine by FTIR method (13)(14)(15)(16)(17)(18) were studied. Thermal desorption methods can also be used for the determination of the types of acid sites and their amounts in the catalysts (5,12,(19)(20)(21)(22).…”

Infrared Spectroscopy as a Probe of Surface Acidity

“…Details have been summarized by Paukshtis and Yurchenko (12) and by Boehm and Knozinger [ 11). In several studies [33,77,78) the relative numbers of aprotonic and protonic acid sites have been determined by pyridine adsorption, which requires knowledge of the ratio of extinction coefficients of e.g. the 19b mode near 1450 cm-I for the coordinated pyridine species and near 1545 cm-I for the pyridinium ion.…”