Synthesis, thermal and structural characterization of alumina-based pillared α-Ti(IV)hydrogenphosphate

The intercalating properties of α-titanium hydrogenphosphate with general formula Ti(IV)(HPO4)2·H2O (denoted as α-TiP in the following) have been evaluated by preparing two precursors, synthesized by intercalation of hydroalcoholic solutions of n-hexylamine and n-octylamine into the layers of α-TiP. The obtained precursors, slightly hydrolyzed, have interlayer distances two, three or four times larger then the starting material. Afterward, several alumina-pillared α-TiP derivatives were prepared by intercalation of an aluminum Keggin-type ion of general formula [AlO4Al12(OH)24(H2O)12]7+, denoted as Al13, into the layers of the precursors. No evidence of the presence of the previously intercalated amines was revealed by studying the thermal behavior of the so-prepared Al-intercalated materials that were subsequently calcined in air at 600 °C, thus providing thermally stable pillared alumina-based materials. BET surface areas on α-TiP-Al2O3 materials are not noticeable high (from 15 to 55 m2 g−1). However, the highest value is four times than that of α-TiP calcined at the same temperature (layered-TiP2O7). Finally, preliminary catalytic tests were performed on 1-butene isomerization at 450 °C for 80 min, and the results confirmed that Brönsted acid sites of the PO3–OH groups of the starting materials not involved in the intercalation are responsible for the results obtained. It was also possible to preliminarily conclude that the strength of the acid sites is from medium to weak.