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Abstract: Nanoparticle silicalite-1 crystallization from clear solutions was followed by nitrogen adsorption at 77K, applied to the products collected from the synthesis solution at different times. Isotherm data were analyzed by t-plot/BET, density functional theory (DFT), and Saito–Foley methods. Variation in the micropore and mesopore/external areas and volumes of the products with time, were in strong agreement with a recent study, which indicated that nucleation that took place after an induction time, was accompanied by an aggregation of a population of smaller particles. A sharp decrease in external surface area was observed parallel to a significant increase in the micropore area of the solid product at this stage of synthesis, when a sudden jump in the effective diameter of the nanoparticles in solution was recorded. Although earlier appearance in the solid products, of small amounts of particles/regions with pore sizes in a range including the pore sizes of silicalite-1, was indicated by both the DFT and Saito–Foley analyses, variation of the Saito–Foley median diameter with synthesis time provided a clear evidence of the significance of this “induction time”, after which particles could grow at a constant linear rate. Nitrogen adsorption at 77K was shown to be a useful tool to monitor the nucleation and crystal growth of silicalite-1 nanoparticles. [Copyright &y& Elsevier]

Abstract: Vapor phase adsorption isotherms of methyl tertiary butyl ether (MTBE) in silicalite-1 at temperatures in the range of 298–600K were measured using a gravimetric analysis system. A maximum saturation loading of 4mol/u.c. was measured. The diffusion coefficients as a function of loading at each temperature were calculated from the differential adsorption uptake data. Diffusivities were observed to increase with loading up to about 1mol/u.c., possibly due to significant adsorption on external surfaces of the particles. Above this value, diffusivities became independent of loading. Additionally, Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations were carried out to estimate the adsorption isotherms and the diffusion coefficients, and the results were compared to those of the experiments. The GCMC simulation results were in reasonable agreement with the experimental data, especially at higher pressures and lower temperatures, where the contribution of interparticle and surface adsorption became marginal. From the MD simulations, MTBE molecules were seen to move very slowly inside the crystal since they spend time at the channel intersections. These simulations were also extended to loadings higher than 4mol/u.c., in order to shed light on the higher adsorption capacities from aqueous solutions previously reported in the literature. The mobility of the MTBE molecules was observed to increase with loading beyond the value of 4mol/u.c., which deserves further investigation. [Copyright &y& Elsevier]