Post-synthesis coating of alumina on the mesopore walls of SBA-15 by ammonia/water vapour induced internal hydrolysis and its consequences on pore structure and acidity

Post-synthesis alumina coating on the pore walls of SBA-15 mesoporous silica was accomplished by internally hydrolyzing preloaded alumina precursor using ammonia/water vapour as hydrolyzing agent at elevated temperature under autogenously generated pressure and subsequent calcination. The resulted alumina-coated materials were characterized by means of N2 adsorption, XRD, TEM, FTIR, TPD of ammonia and pyridine adsorption. The N2 adsorption and XRD results showed that during the coating procedure mesopore walls were restructured resulting in improvement in their uniformity which was diminished by high loading of alumina. The restructuring process was influenced by temperature and duration of NH3/H2O vapour treatment. The coated alumina layer was anchored on the pore walls via Si–O–Al linkages and thus both Bronsted and Lewis acid sites were generated after coating.