Novel and versatile solid superbases derived from magnesium–zirconium composite oxide and their catalytic applications

Abstract

Versatile solid superbases were derived from magnesium–zirconium composite oxide and KOH through thermal treatment in a N₂ flow. The magnesium–zirconium composite oxide was prepared by a modified co-precipitation technique with reflux-digestion in basic solution and then mixed with KOH through grinding. The as-prepared solid superbases were characterized by low-temperature N₂ physisorption, powder X-ray diffraction, and Fourier transformation infrared spectrophotometry. The superbasic sites were characterized by the use of Hammett indicators and CO₂ temperature-programmed desorption methods. We found that there are ample superbasic sites (0.590 mmol g⁻¹) on the surface with strength in the 26.5 ≤ H₋ < 33.0 range. The as-prepared solid superbase catalyst was found to show excellent catalytic activity towards Knoevenagel condensation, Michael addition and transesterification reactions. The findings open up a new route for the synthesis of new functional superbases using composite oxides prepared by reflux-digestion in basic solution as supports.