Fabrication of Monodisperse Porous Zirconia Microspheres and Their Phosphorylation for Friedel–Crafts Alkylation of Indoles

Abstract

Monodisperse porous zirconia (ZrO2) microspheres with nanocrystallized framework were fabricated by impregnation of porous polymer microspheres as a novel hard template with zirconia precursors followed by calcination to remove the template. Porous phosphorylated zirconia (PhZr) microspheres were prepared by further treating porous zirconia microspheres with phosphoric acid. The morphology, structure, and properties of these microspheres were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption/desorption measurement, FT-IR, and X-ray powder diffraction. The as-prepared zirconia and phosphorylated zirconia microspheres showed uniform particle size and well-defined morphology. The phosphorylated zirconia microspheres served as highly active solid acid catalysts for Friedel-Crafts alkylation of indoles with chalcones and could be reused for 22 cycles with negligible loss of activity. In situ pyridine-adsorbed FT-IR analysis of the best performing PhZr microspheres suggested the presence of both Lewis and Brønsted acid sites, and the total acidity as measured by temperature-programmed desorption of ammonia (NH3-TPD) was 328 μmol·g(-1).