Preparation of a novel solid base catalyst of CaO covered with SiO2

Solid base catalysts composed of CaO covered with 5–20 mol% SiO2 (SiO2/CaO) were prepared by deposition of Si(OC2H5)4 on a Ca(OH)2 surface in an ethyl acetate solution, followed by thermal decomposition in air at 773–1023 K. The CaO catalysts covered with 5–20 mol% Si and treated at 773–973 K showed sufficient activity for a retro-aldol reaction to convert diacetone alcohol (4-hydroxy-4-methyl-2-pentanone) into acetone at 299 K. The catalyst heat-treated at 1073 K was inactive. The dissolution of Ca2+ into the polar solvent diacetone alcohol was observed in all catalysts prepared by single-deposition procedures. A double-deposition method, covering the SiO2/CaO catalysts again with SiO2, was effective in inhibiting the dissolution of Ca2+. The catalyst prepared by the double-deposition method showed excellent tolerance toward H2O contained in the substrate.