Thermally stable, silica-based amorphous porous mixed oxides prepared by sol–gel procedures

The sol–gel process has been used to prepare porous amorphous mixed oxides (AM) of Si with Al, Ti, and Zr, covering a wide range of composition. The effect of heating on porosity, crystallinity, and microstructure has been investigated by a variety of methods (Ar-adsorption isotherms, high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray analysis (EDX), X-ray powder diffraction (XRD), FTIR in diffuse reflectance mode (DRIFTS). The effect of impregnation and doping on the temperature stability of selected oxides is shown. Several compositions show a surprisingly high temperature stability. An amorphous porous AM-Si10Al (amorphous mixed-oxide with 10 mol% SiO2 in Al2O3), stabilised with an additional 5 mol% silica, has been obtained, whose microstructure is stable up to 1400°C with no indication of phase separation or nanocrystal formation. A detailed characterisation of this material and its application as support material in methane combustion is presented. The study shows that amorphous mixed oxides may offer a promising new approach to the development of high temperature stable porous materials.