Polystyrene/silica microspheres with core/shell structure as support of tungstophosphoric acid

• Tungstophosphoric acid on core/shell polystyrene/silica microspheres were prepared.
• Spheres presented a narrow size distribution and SiO2 nanoparticles uniform layer.
• Mesoporous tungstophosphoric acid impregnated solids were achieved.
• Tungstophosphate anion with undegraded Keggin structure is present in the solids.
• Solids have very strong acid sites being suitable for use in acid catalyzed reactions.

The immobilization of tungstophosphoric acid (TPA) on polystyrene/silica microspheres with core/shell structure by the incipient wetness impregnation technique was studied. The materials were synthesized employing polystyrene (PS) spheres or polystyrene spheres with the addition of 3-amino-1-propene as core, which were coated with silica by a modified Stöber method, using tetraethylorthosilicate as precursor. Spheres with a narrow size distribution and a uniform layer formed by silica nanoparticles were obtained, as observed by SEM and TEM. After impregnation with TPA, the samples were calcined at 200 °C in order to obtain the final materials. The solids impregnated with TPA presented N2 adsorption–desorption isotherms characteristic of mesoporous materials. In addition, the characterization by FT-IR and 31P NMR of all the solids impregnated with TPA gave evidence of the presence of the tungstophosphate anion with Keggin structure, and by potentiometric titration it was estimated that the solids present very strong acid sites. So, they are good candidates to be used in reactions catalyzed by acids, specifically for imidazole synthesis.

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