Zeolites have consistently been a topic of intense research because of their tunable catalytic properties, the result of the incorporation of different elements (aluminum, germanium, boron, etc.) in the silica crystalline framework. For many years, alumina incorporation has been shown to result in different crystalline structures and particle morphologies; however, the majority of studies focusing on the nucleation and growth of zeolite materials have focused solely on all-silica syntheses. Here, we expand on our recent research of the self-assembly of silica in basic solutions of small organic cations by studying the impact of alumina on these systems.

The effect aluminum on the initial condensation of silica in basic solutions of organic and inorganic cations is analyzed using conductivity, pH, NMR spectroscopy and small angle scattering methods. The addition of alumina to these solutions decreases substantially the point at which nanoparticles form. At high alumina concentrations, the particles are smaller than those found in all-silica solutions and spherical in shape. We argue, using equilibrium thermodynamic theory, that the composition should be rich in aluminum. In the case of sodium, larger rather than smaller particles are observed and the data strongly suggests that sodium cations are being incorporated within the inorganic silica/alumina core, as opposed to organic cations that appear to be excluded from such clusters. As was the case for the pure-silica system, important insights are gained by making analogies to the behavior of mixed surfactant systems.