ACIDITY AND CATALYTIC ACTIVITY OF ALPO4-B2O3 AND AL2O3-B2O3 (5-30 WT-PERCENT B2O3) SYSTEMS PREPARED BY IMPREGNATION

The surface acidic properties of a series of AlPO4-B2O3 (APB) and Al2O 3-B2O3 (AIB) systems, prepared by supporting B2O3 from boric acid solu tions using an incipient wetness method and containing different boria loading (5-30 wt%), have been studied by adsorption (at 573 K) of pyr idine (PY) and 2,6-dimethylpyridine (DMPY) using a pulse-chromatograph ic method. Acidity measurements show that Lewis and Bronsted sites exi st in the APE and AIB systems at all boria loadings. Moreover, the con centration of Bronsted acid sites increases with bona content. This in creased surface Bronsted acidity is responsible for their improved per formance in the cyclohexene skeletal isomerization (SI) reaction, to 1 - and 3-methylcyclopentenes (MCPE), especially at high boria loadings. Comparison of the activity and acidity measurements points to a corre lation between the activity and the number of Bronsted acid sites on t he APE and AIB catalysts. Moreover,at high boron contents, AlB catalys ts are more acidic and hence more active than APE catalysts. Furthermo re, the more acidic catalyst (AlB, with 30 wt% boria) also showed cata lytic activity for the cyclohexene hydrogen transfer (HT) reaction lea ding to methylcyclopentane and cyclohexane. (C) 1998 Elsevier Science B.V.