A new crystal phase of calcium stannate CaSn2O4(OH)2 and its physico-chemical properties
Abstract
Thermovapour treatment (TVT) of SnO2 and CaO oxides in an autoclave at 673 K leads to the formation of isometric CaSnO3 perovskite-type crystals. TVT at 623 K leads to a previously unknown CaSn2O4(OH)2 phase with lamellar crystals. The structure of the new compound CaSn2O4(OH)2 was determined using powder X-ray diffraction and characterized with scanning electron microscopy, thermogravimetry–differential scanning calorimetry (TG-DSC) analysis, and IR spectroscopy. CaSn2O4(OH)2 crystallizes in space group Aba2 with Z = 4. The crystal structure consists of double layers formed from [SnO6] octahedra alternating with layers formed from [CaO8] tetragonal antiprisms. The TG-DSC study shows that the new compound CaSn2O4(OH)2 is stable up to 973 K. The thermodynamic parameters of CaSn2O4(OH)2 analysized using DFT in comparison with CaSn(OH)6 and CaSnO3. The synthesized lamellar CaSn2O4(OH)2 exhibits high catalytic activity and selectivity to C6+ products in the aldol condensation of acetone at 673 K and 12.0 MPa.
