FT-IR STUDIES ON LIGHT OLEFIN SKELETAL ISOMERIZATION CATALYSIS III - SURFACE-ACIDITY AND ACTIVITY OF AMORPHOUS AND CRYSTALLINE CATALYSTS BELONGING TO THE SIO2-AL2O3 SYSTEM
M. Trombetta et al., FT-IR STUDIES ON LIGHT OLEFIN SKELETAL ISOMERIZATION CATALYSIS III - SURFACE-ACIDITY AND ACTIVITY OF AMORPHOUS AND CRYSTALLINE CATALYSTS BELONGING TO THE SIO2-AL2O3 SYSTEM, Journal of catalysis (Print), 179(2), 1998, pp. 581-596
The surface acidity of both amorphous and crystalline materials belong
ing to the SiO2-Al2O3 system (i.e., amorphous silicas, amorphous silic
a-aluminas with different Al contents, HZSM5 and H-ferrierite (FER) ze
olites, and silicated and pure gamma-Al2O3) have been studied using th
e FT-IR spectroscopy of the surface hydroxy groups and of adsorbed ace
tonitrile (AN) and pyridine (Py). Lewis bonded and H-bonded species of
AN have been observed, while a protonated form of adsorbed AN has bee
n characterized on HZSM5. A molecular sieve effect has been found for
Py adsorption on FER and HZSM5. The catalytic activity of these materi
als in the skeletal isomerization of 1-butene to isobutene has also be
en investigated. The Bronsted surface acidity scale found correlates w
ell with the catalytic activity in 1-butene conversion, measured after
20-40 min time on stream. The selectivity to isobutene follows nearly
an inverse trend, except for FER, which shows both higher activity an
d higher selectivity than silica-alumina, quite good resistance to cok
ing, and selectivity increasing with time on stream. Comparative analy
sis of the behavior of these catalysts and of the spectrum of their su
rface OH groups gives new light on the structure of the acidic OHs on
materials belonging to the SiO2-Al2O3 system. The usefulness of zeolit
e and alumina-based catalysts for skeletal isomerization of n-butene t
o isobutene is also briefly discussed. (C) 1998 Academic Press.