Aerosol synthesized mesoporous silica containing high loading of alumina and zirconia

Abstract

Mesoporous silica particles with high loadings of Al (Si/Al molar ratio 20 to 2) and Zr (Si/Zr molar ratio 37 to 5) were synthesized by evaporation induced self assembly (EISA) using an aerosol route. The aerosol synthesis process allows us to produce mesoporous silica particles with a high loading of heteroelements (Al or Zr) while retaining uniformity of composition and an ordered pore structure. ²⁷Al NMR TRAPDOR experiments indicate that Al is in close proximity to Si, within the mesoporous silica structure. The submicron particles are spherical and consist of interconnected, hexagonally ordered domains of pores. The hydrothermal stability of these composite mesoporous silica particles was tested in 10 mol% water vapor at various temperatures (500 °C to 750 °C) and also in boiling water. Pure mesoporous silica particles were not stable under hydrothermal treatment and their surface area dropped from 1300 m² g⁻¹ to 300 m² g⁻¹ after treatment at 750 °C in steam. In contrast, the aluminium and zirconium containing powders retained a surface area of 800 m² g⁻¹ after similar treatment. The improvement in hydrothermal stability was found to be dependent on Al and Zr content. The three-dimensional interconnected network of pores, higher loading of heteroelement and their hydrothermal stability, make these spherical particles attractive as adsorbents and as supports for heterogeneous catalysts.