Physicochemical Characterisation and Catalytic Activity of Primary Amine Templated Aluminosilicate Mesoporous Catalysts

Abstract

Primary amines are used as structure-directing agents in the room temperature assembly of aluminosilicate inorganic species to yield mesoporous materials with physical and textural properties similar to those of MCM-41 but with substantially higher Brønsted acidity. Si and Al are incorporated into the mesoporous framework in proportions dependent on the gel Si/Al ratio. Calcination of the as-synthesised material to remove the occluded amine generates Brønsted acid sites which (depending on Si/Al ratio) are stronger or comparable in strength to those on zeolite-HY (Si/Al=3.65) but weaker than those on ultrastable-Y zeolite (USY). The materials, designated Al-MMS, exhibit higher Brønsted acidity and catalytic activity for the cracking of cumene compared to equivalent aluminosilicate MCM-41 materials or to amorphous silica-alumina and show considerable stability to catalytic deactivation. Al-MMS samples with Si/Al ratio ≤20 have catalytic activity higher than the zeolite-HY but exhibit a lower rate of deactivation compared to the zeolite. Ageing of the materials (for 1 year in the calcined form) has no significant effect on their acidity and catalytic activity. Hexagonal ordering and total Brønsted acidity (but not acid strength) of the Al-MMS materials may be improved by using prepolymerised aluminosilicate inorganic precursors.