PS-SO3H@phenylenesilica with yolk–double-shell nanostructures as efficient and stable solid acid catalysts

• Novel solid acid catalysts with yolk–shell nanostructures have been synthesized.
• The solid acids showed higher activity in the Friedel–Crafts alkylation reaction.
• The solid acids showed excellent stability in the Friedel–Crafts alkylation reaction.
• The solid acids exhibit higher activity and thermal stability than Amberlyst-15.
• The relation of activity with acid strength of solid acids was investigated.

Efficient and stable solid acids have been successfully synthesized by sulfonation of polystyrene (PS) in the hollow interiors of silica-based hollow nanostructures. It was found that larger and smaller inner void spaces result in the formation of PS-SO3H@phenylenesilica respectively with double-shell (DSNs) and yolk–double-shell nanostructure (YDSNs). PS-SO3H@phenylenesilica with DSNs and YDSNs nanostructure shows comparable activity and is more active than Amberlyst-15 in the esterification reaction. PS-SO3H@phenylenesilica with YDSNs nanostructure affords higher activity than that with DSNs nanostructure in the Friedel–Crafts alkylation of toluene with 1-hexene, which is mainly attributed to the fact that the unique YDSNs nanostructure could slow down the swelling rate of PS-SO3H during the catalytic process. More importantly, PS-SO3H@phenylenesilica with YDSNs nanostructure showed much higher recycle stability than Amberlyst-15 in the Friedel–Crafts alkylation of toluene with 1-hexene, probably due to the high thermal stability of the sulfonic acid group and the unique YDSNs nanostructure.

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