Behaviour of Amorphous Aluminosilicates towards Ageing by High-Temperature Steaming

The structure of amorphous aluminosilicates obtained by grafting silicon on alumina (Si/Al2O3) mostly remains the same after ageing by steaming. The rearrangement of surface silicon species on the facets of -alumina slightly decreases the number of BrOnsted acid sites, which is determined through ethanol adsorption followed by thermogravimetry as well as m-xylene isomerisation. Al/SiO2 prepared by grafting aluminium on silica undergoes sintering of the silica support and the agglomeration of the surface aluminium species during steaming. This process leads to a sharp decrease in the number of BrOnsted acid sites, which are associated with the dispersed aluminium species, and dehydroxylation of the silica surface.