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The aldol condensation of acetone under supercritical conditions at 300–400°C and 11.0 MPa was carried out on BaSnO3-450 and BaSnO3-750 catalysts prepared by calcination of BaSn(OH)6 at 450 and 750°C, respectively. Conducting the reaction under these conditions makes it possible to overcome the problem of catalyst deactivation by coking and to obtain valuable chemicals with high selectivity. At 300°C, both catalysts provide selectivity of 85–87% to isomeric mesityl oxides (C6 products). At 400°C with the BaSnO3-450 catalyst, the selectivity significantly changes from C6 to C9 (phorones). Powder X-ray diffraction and TEM data attest to the multiphase nature of the samples, which contain barium stannates, barium carbonate, and tin oxide. It was found that the catalyst structure rearranges in situ, which greatly affects the catalytic properties and is most pronounced for BaSnO3-450. [ABSTRACT FROM AUTHOR]

The aldol condensation of acetone was carried out under the conditions of the supercritical state of the reagent (350 °C, 8 MPa; 400 °C, 12 MPa) on catalysts prepared by the thermal treatment of CaSn(OH)6 at 450 and 750 °C. The X-ray amorphous phase of CaSnO3 transforms into crystalline calcium stannate as the thermal treatment temperature increases from 450 to 750 °C. At 350 °C and 8.0 MPa, the selectivity of the reaction to mesityl and isomesityl oxides is about 85% (for both samples), but the conversion of acetone is much higher on CaSnO3 after it has been thermally treated at 750 °C. The reuse of the CaSnO3-450 catalyst led to its transformation. The conversion of acetone increases, and the reaction parameters (conversion and selectivity) reach values characteristic of CaSnO3-750. The catalyst structures were studied by XRD and scanning and high-resolution transmission electron microscopies. [ABSTRACT FROM AUTHOR]