High‐Zirconium‐Content Nano‐Sized Bimodal Mesoporous Silicas

Abstract Silica‐based nanoparticulated bimodal mesoporous materials with high Zr content (43 ≥ Si/Zr ≥ 4) have been synthesized by a one‐pot surfactant‐assisted procedure from a hydroalcoholic medium using a cationic surfactant (CTMABr = cetyltrimethylammonium bromide) as structure‐directing agent, and starting from molecular atrane complexes of Zr and Si as hydrolytic inorganic precursors. This preparative technique allows optimization of the dispersion of the Zr guest species in the silica walls. The bimodal mesoporous nature of the final high surface area nano‐sized materials is confirmed by XRD, TEM, and N 2 adsorption–desorption isotherms. The small intraparticle mesopore system (with pore sizes around 2–3 nm) is due to the supramolecular templating effect of the surfactant, while the large mesopores (around 12–24 nm) have their origin in the packing voids generated by aggregation of the primary nanometric mesoporous particles. The basicity of the reaction medium seems to be a key parameter in the definition of this last pore system. The effects induced by the progressive incorporation of Zr atoms on the mesostructure have been examined, and the local environment of the Zr sites in the framework has been investigated by UV/Vis spectroscopy. Observations based on the consequences of post‐treatments of the as‐synthesized materials with HCl/ethanol mixtures corroborate that the atrane method leads to Zr‐rich materials showing enhanced site accessibility and high chemical homogeneity throughout the pore walls. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)