Heterogeneous catalysts for the Friedel-Crafts alkylation

Trivalent metal ions supported onto silica from rice husk ash as alternative catalysts for the alkylation of aromatics

RHA-Al, RHA-Ga, RHA-In and RHA-Fe heterogeneous catalysts were prepared by modifying the surface of silica extracted from rice husk ash (RHA) with Al3+,Ga3+, In3+ and Fe3+ ions, respectively.

The as-synthesized solid catalysts showed good textural and structural properties as it was confirmed by the physico-chemical techniques such as FT-IR, 29Si MAS NMR, solid-state NMR and ESR for metal nuclei,powder XRD, N2-adsorption, SEM-EDX, TEM and ICP-MS elemental analysis.

The heterogeneous catalysts exhibited good activity for the benzylation and tert- butylation of benzene and some substituted benzenes with benzylchloride (BC) and tert-butylchloride (TBC),respectively.

For both reactions, the activity of the catalysts was observed to be positively influenced with increasing reaction temperature, catalyst weight and percentage loading of active species.

The catalytic activity was observed to decrease in the following order:RHA-Fe ˃ RHA-In ˃ RHA-Ga ˃˃ RHA-Al, which was correlated well with the redox potential of the supported metal ion rather than its Lewis acidity.

The catalysts were reusable and stable against leaching.