Zeolite growth by addition of subcolloidal particles: Modeling and experimental validation

Seeded growth of tetrapropylammonium (TPA)-silicalite-1 is studied using si mulations and dynamic light scattering, atomic force microscopy, and transm ission electron microscopy experiments. The effects of the total silica con centration, temperature, and total seed concentration are examined. When th e composition of silica in solution is above a critical value, growth is ob served. In such a case, ;he 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 similar to 90 kJ/mol for a range of seed concentrations. Transmission elect ron microscopy and dynamic light scattering indicate the presence of subcol loidal particles. Simulations of the growth of a static particle in a suspe nsion of subcolloidal particles are carried out. Good agreement with experi mental results regarding the growth rate and the apparent activation energy is possible by considering Derjaguin-Landau-Verwey-Overbeek (DLVO) interac tions with electrostatic repulsion described with a constant surface charge model. The type of interaction was also verified with atomic force microsc opy force measurements between a silicalite surface and a glass sphere. By use of these types of interactions, it is also possible tea explain the sta bility 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, grow th of silicalite seeds proceeds by a mechanism with the rate-limiting step being the addition of subcolloidal particles.