Procedure for the synthesis of AlSBA-15 with high aluminium content: Characterization and catalytic activity

Abstract

Abstract In this study, AlSBA-15 materials with low nSi/nAl ratio were hydrothermally prepared by using three different acids, i.e. HCl, HNO3 and H2SO4, aiming to investigate the effect of the synthesis environment on their physicochemical properties. The resulting aluminium substituted molecular sieves were used as a supports for Pt catalysts. The AlSBA-15 materials and the Pt/AlSBA-15 catalysts were characterised by different techniques (N2 sorption, XRD, Py–FTIR, 27Al MAS NMR, CO chemisorption, TEM and SEM) and tested in n-heptane hydroconversion. It was found that the crystallisation of AlSBA-15 structure under the use of HNO3 led to the formation of AlSBA-15 with the highest amount of Al atoms in tetrahedral coordination. Depending on the AlSBA-15 preparation conditions, the Pt/AlSBA-15 catalysts displayed different physicochemical features, especially in term of acidity. As a consequence of the highest substitution of Al in tetrahedral positions in AlSBA-15 sample synthesised under the use of HNO3, the corresponding Pt catalyst exhibited the highest Bronsted acid sites concentration. The results of n-heptane hydroconversion showed that, this catalyst provided the highest yield of the most desired high-octane number products, i.e. multibranched heptane isomers. At the same time it was less selective towards hydrocarbons displaying the boiling temperatures higher than this of n-heptane (they are produced in cyclisation and aromatization) which are the precursors of carbonaceous deposits.