(770b) Tuning Porosity in Metal – Silicate Catalysts: Targeted Mesoporous Systems without the Use of Templates

Utilizing a cubic silicate building block and nonaqueous condensation reactions, a wide variety of micro- and mesoporous silicate matrices containing atomically dispersed metals (M = Si, Ti, Zr, W) have been synthesized.  The key to controlling the total surface area and porosity exhibited by these materials involves adjusting the stoichiometric ratio of linking reagent (typically the chloride complex of the metals listed above) and the tin functionalized cubic silicate building block, Si₈O₂₀(SnR₃)₈ (R = Me, Bu).  At low M : cube ratios (< 1) low surface area oligomeric structures are formed.  As the ratio is increased to ~2.5 the BET surface area rapidly rises to between 100 – 500 m²/g and the matrices are microporous.  For M : cube ratios between 2.5 and 3.0 the surface area increases to a maximum of 900 m²/g and the amorphous matrices exhibit mixtures of micro and broadly distributions of mesopores.  Beyond ratios of 3.0 the mesopore component increases to 70% according to the BJH model.  Of note is the observation that consecutive doses of the metal chloride linking agents above fall on the same stoichiometry vs. surface area/pore size plot.  These results illustrate a simple method of targeting both pore size and metal site identity in the construction of nanostructured catalysts.