Fm. Bautista et al., FLUORIDE TREATMENT OF ALPO4-AL2O3 CATALYSTS .2. POISONING EXPERIMENTSBY BASES FOR CYCLOHEXENE CONVERSION AND CUMENE CRACKING, Catalysis letters, 24(3-4), 1994, pp. 293-301
Bronsted acid sites on fluoride-modified AlPO4-Al2O3 (2.5 wt% F; APAl-
P-2.5F) catalyst are poisoned by the presence of 2,6-dimethylpyridine
(DMPY) and hexamethyldisilazane (HMDS), thus decreasing the catalytic
activity for cyclohexene and cumene reaction processes, while the effe
ct of pyridine (PY) was scarce. Besides, the drop in activity for cycl
ohexene conversion was accompanied by a change in reaction selectivity
so that hydrogen transfer sites are much more sensitive to base poiso
ning (getting greater as the poisoning effect increased) than isomeriz
ation sites. Moreover, surface trimethylsilyl (TMS) complexes (formed
by covalent reaction of HMDS with surface hydroxyls) decomposed and th
us, the activity progressively increased at increasing time intervals,
thus reaching greater values (at ca. 4 h) than the unpoisoned APAl-P-
2.5F catalyst. So, DMPY was more suitable than PY and HMDS for the poi
soning of Bronsted acid sites on APAl-P-F catalyst.