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

Citation
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
Citations number
71
Categorie Soggetti
Chemistry Physical
ISSN journal
00219517
Volume
179
Issue
2
Year of publication
1998
Pages
581 - 596
Database
ISI
SICI code
0021-9517(1998)179:2<581:FSOLOS>2.0.ZU;2-H
Abstract
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.