Synthesis of highly active solid base catalysts of SrO-ZrO2 and SrO-SiO2 by solid-liquid interface reactions of hydrated strontium hydroxide with metal alkoxides

Highly dispersed SrO in amorphous ZrO2 or SiO2, SrO-ZrO2, and SrO-SiO2 mixed oxides were synthesized by applying the solid-liquid interface reaction of Sr(OH)2 center dot 8 H2O in the solid phase with an equal number of moles of Zr(OC3H7)4 or with twice the number of Si(OC2H5)4 moles dissolved in 2-propanol. After heat treating at 723 K, the SrO-ZrO2 catalyst exhibited a higher activity than the conventional solid base MgO catalyst for the base -catalyzed retroaldol reaction of diacetone alcohol. The catalytic activity of SrO-ZrO2 was higher by a factor of 1.5 than that of MgO prepared by the thermal decomposition of hydrated magnesium oxalate (MgC2O4 center dot 2H2O). By contrast, the highest activity of SrO-SiO2 obtained by thermal activation at 673 K was much lower than that of MgO. The active SrO-ZrO2 catalyst was composed of catalytically inactive species of SrZrO3, and small amounts of Sr(OH)2 and SrCO3. The expected active species of SrO was not detected in powder X-ray diffraction analysis in any sample. The formation of SrO in small crystal size dispersed in amorphous ZrO2 was strongly expected. Similar results were obtained in the SrO-SiO2 sample. An active site formed on SrO-ZrO2 surface is proposed.