Dealumination and realumination of microcrystalline zeolite beta: an XRD, FTIR and quantitative multinuclear (MQ) MAS NMR study

Zeolite beta was dealuminated by treatment with hydrochloric acid and realuminated by reaction of the dealuminated zeolite beta with aluminium isopropoxide at room temperature. FTIR and H-1 MAS NMR spectroscopy showed that the extent of the generated Bronsted acidity was similar to that of the parent material before dealumination. The distribution of aluminium in zeolite beta and in dealuminated and realuminated zeolite beta was investigated by means of multiple quantum (MQ) Al-27 MAS NMR spectroscopy. Dealumination occurred preferentially at specific T-sites. Subsequent reaction with aluminium isopropoxide led to the preferential insertion of aluminium into the same crystallographic sites by the occupancy of the structural vacancies. The controlled amount of aluminium isopropoxide and dry conditions, under which the reaction took place, limited the formation of extraframework material to some extent.