Acidity and catalytic activity of AlPO4–B2O3 and Al2O3–B2O3 (5–30 wt% B2O3) systems prepared by impregnation Original Research Article

The surface acidic properties of a series of AlPO4–B2O3 (APB) and Al2O3–B2O3 (AlB) systems, prepared by supporting B2O3 from boric acid solutions using an incipient wetness method and containing different boria loading (5–30 wt%), have been studied by adsorption (at 573 K) of pyridine (PY) and 2,6-dimethylpyridine (DMPY) using a pulse-chromatographic method. Acidity measurements show that Lewis and Brønsted sites exist in the APB and AlB systems at all boria loadings. Moreover, the concentration of Brønsted acid sites increases with boria content. This increased surface Brønsted acidity is responsible for their improved performance 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 correlation between the activity and the number of Brønsted acid sites on the APB and AlB catalysts. Moreover, at high boron contents, AlB catalysts are more acidic and hence more active than APB catalysts. Furthermore, the more acidic catalyst (AlB, with 30 wt% boria) also showed catalytic activity for the cyclohexene hydrogen transfer (HT) reaction leading to methylcyclopentane and cyclohexane.