Zeolite Growth by Addition of Subcolloidal Particles: Modeling and Experimental Validation

Seeded growth of tetrapropylammonium (TPA)−silicalite-1 is studied using simulations and dynamic light scattering, atomic force microscopy, and transmission electron microscopy experiments. The effects of the total silica concentration, temperature, and total seed concentration are examined. When the composition of silica in solution is above a critical value, growth is observed. In such a case, the size of the seeds increases linearly with time, with a growth rate that is not significantly affected by the total silica concentration. Growth appears to be activated with an activation energy of ∼90 kJ/mol for a range of seed concentrations. Transmission electron microscopy and dynamic light scattering indicate the presence of subcolloidal particles. Simulations of the growth of a static particle in a suspension of subcolloidal particles are carried out. Good agreement with experimental results regarding the growth rate and the apparent activation energy is possible by considering Derjaguin−Landau−Verwey−Overbeek (DLVO) interactions with electrostatic repulsion described with a constant surface charge model. The type of interaction was also verified with atomic force microscopy force measurements between a silicalite surface and a glass sphere. By use of these types of interactions, it is also possible to explain the stability of the seeded suspension and show that only a relatively narrow size distribution of growth precursors participate in the growth of the seeds. Our results support the possibility that under the conditions studied, growth of silicalite seeds proceeds by a mechanism with the rate-limiting step being the addition of subcolloidal particles.