TY - JOUR
T1 - Brønsted acidity of Al/SBA-15
AU - Koekkoek, A.J.J.
AU - Veen, van, J.A.R.
AU - Gerritsen, P.B.
AU - Giltay, P.
AU - Magusin, P.C.M.M.
AU - Hensen, E.J.M.
PY - 2012
Y1 - 2012
N2 - To increase the content of well-dispersed aluminium in Al/SBA-15 and its Brønsted acidity, a water-free synthesis method involving a Si-O-Al precursor was employed to preparea series of Al/SBA-15 of widely varying composition. The materials were characterized with ICP, BET, TEM, 27Al MAS NMR and IR spectroscopy and compared to conventionally prepared Al/SBA-15. For low Al content (Si/Al >10),the conventional approach leads to highly dispersed, predominantly isolated Al with well-ordered mesopores.Athigher Al content, the order decreasedor was even completely lost.In general, this led to the agglomeration of Al species on the surface. Although in most cases a substantial part of Al atomsexhibit tetrahedral coordination indicating their high dispersion and interaction with the silica, the overall Brønsted acidity of these Al/SBA-15-type materials is very low. The overall acidity of all Al/SBA-15 is of the same order as amorphous silica-alumina. By IR spectroscopy of H/D exchange with perdeuterobenzene, it was found that the intrinsic acidity of the acid sites in Al/SBA-15 is similar to that in zeolites and amorphous silica-alumina, thus further confirming that acid site concentration dominates differences in acidity of aluminosilicas.
AB - To increase the content of well-dispersed aluminium in Al/SBA-15 and its Brønsted acidity, a water-free synthesis method involving a Si-O-Al precursor was employed to preparea series of Al/SBA-15 of widely varying composition. The materials were characterized with ICP, BET, TEM, 27Al MAS NMR and IR spectroscopy and compared to conventionally prepared Al/SBA-15. For low Al content (Si/Al >10),the conventional approach leads to highly dispersed, predominantly isolated Al with well-ordered mesopores.Athigher Al content, the order decreasedor was even completely lost.In general, this led to the agglomeration of Al species on the surface. Although in most cases a substantial part of Al atomsexhibit tetrahedral coordination indicating their high dispersion and interaction with the silica, the overall Brønsted acidity of these Al/SBA-15-type materials is very low. The overall acidity of all Al/SBA-15 is of the same order as amorphous silica-alumina. By IR spectroscopy of H/D exchange with perdeuterobenzene, it was found that the intrinsic acidity of the acid sites in Al/SBA-15 is similar to that in zeolites and amorphous silica-alumina, thus further confirming that acid site concentration dominates differences in acidity of aluminosilicas.
U2 - 10.1016/j.micromeso.2011.11.019
DO - 10.1016/j.micromeso.2011.11.019
M3 - Article
SN - 1387-1811
VL - 151
SP - 34
EP - 43
JO - Microporous and Mesoporous Materials
JF - Microporous and Mesoporous Materials
ER -