Silica-supported dodecatungstophosphoric acid (HPW) and Nafion-H were prepared using the ball-milling technique. The samples were characterized and used in catalytic transformations and their properties were compared to those of catalysts made by conventional methods.

Catalyst characterization were performed by physical (BET surface, SEM, DSC, XRD, DRIFT and Raman spectroscopy) and chemical (acid–base titration) methods. Catalytic properties were studied in a range of chemical transformations, which can be induced by electrophilic catalysts including Friedel–Crafts reactions (alkylation of toluene with benzyl alcohol, acylation of anisole with acetic anhydride) and the dimerization of alpha-methylstyrene.

Milling conditions (stainless steel or polystyrene apparatus, milling time), loading of the active components, and the type of support were found to have profound effects on the physical characteristics and catalytic performance of the samples. Ball-milled HPW-on-silica samples prepared under appropriately selected conditions exhibit catalytic properties similar to catalysts made by impregnation. HPW in ball-milled samples, in turn, proved to be more resistant to extraction with polar solvents (hot methanol) and these catalysts display higher stability in recycling studies. Supported Nafion-H samples prepared by ball-milling show high activities in test reactions. The best catalyst sample exceeds the performance of SAC-13, a commercial Nafion-silica nanocomposite catalyst in the selective synthesis of 1,1,3-trimethyl-3-phenylindane in the dimerization of 2-phenylpropene. The preparation of catalysts of high catalytic performance requires the use of optimal milling time, because particle coalescence and the resulting decrease in BET surface area hinder the accessibility of the active sites.

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