Transformation of Discrete Amorphous Aluminosilicate Nanoparticles into Nanosized Zeolites

Abstract

The effect of amorphous aluminosilicate precursor nanoparticles on the formation of nanosized zeolites with faujasite (FAU) and sodalite (SOD) type frameworks is illustrated using a new synthetic strategy to prepare nanosized zeolites with tailored particle size distribution, morphology, and structure. This two‐step synthesis procedure includes the formation of colloidal suspensions followed by separation of the amorphous precursor nanoparticles, and their subsequent transformation into nanosized crystals by treatment with alkali suspensions (NaOH) solutions only. The selective transformation of the amorphous nanoparticles into FAU and SOD nanosized crystals is studied at atomistic and microscopic levels using 29Si and 23Na nuclear magnetic resonanse (NMR) spectroscopy, X‐ray powder diffraction, and N2 physisorption, respectively. The presence of sodalite cages occluding highly mobile sodium in the amorphous nanoparticles is confirmed by 23Na‐1H D‐HMQC NMR spectroscopy. The subsequent treatment of these amorphous precursor particles with aqueous sodium hydroxide illustrates that the cations are not only charge compensators but also inorganic templates stabilizing sodalite cages during the long‐range ordering in the amorphous particles.

Zeolite for Potential Toxic Metal Uptake from Contaminated Soil: A Brief Review

“…The most commonly formed zeolites are zeolite A (LTA), faujasite, zeolite P and sodalite ( Figure 6). In the last few decades, many researches have focused on the formation of nanozeolites showing advanced applications in many contexts such as medicine, catalysis, or the food industry [93][94][95].…”

Synthesis of Dendritic ZSM-5 Zeolite through Micellar Templating Controlled by the Amphiphilic Organosilane Chain Length

“…Several strategies have been proposed for overcoming steric and diffusional constraints in zeolites. The reduction of the zeolite crystal size (nanozeolites) is one of the most widely studied alternatives. − Likewise, another interesting strategy consists of the introduction of a secondary porosity that may lie in the supermicro-, meso-, and macropore ranges (hierarchical zeolites), which has arisen a huge amount of interest during the past 15 years. − In comparison with conventional microporous zeolites, hierarchical ones have shown a number of relevant advantages derived from their enhanced accessibility. Thus, the presence of a large share of mesopore surface area, which may represent up to 50% of the overall surface area, has made possible their use as efficient catalysts in a large variety of chemical transformations involving bulky reactants or products, unable to enter or leave the zeolite micropores .…”

Acid Catalysis over Low-Silica Faujasite Zeolites

“…7,8 Remarkably, ion exchange of low-silica FAU materials using 0.01 M NH 4 NO 3 does not allow occluded alkali cations within small-pore sodalite cages to be removed, but instead only removes Na + circumscribed by large pore 12-membered ring supercages. Na + cations act as inorganic templates to stabilize sodalite cages during zeolite crystallization, 9 and we surmise that the characteristic of lowsilica FAU to limit H + exchange to supercages enables occluded Na + cations within sodalite cages to stabilize the framework for H + -catalyzed reactions at ∼800 K. Protons on low-silica FAU materials engendered upon moderate ion exchange can be associated with two distinct crystallographic positions within the supercage and exhibit different reactivity for high-temperature protolytic reactions of propane. We used a combination of techniquesincluding probe molecule infrared spectroscopy, synchrotron X-ray diffraction (XRD), and Ar-adsorptionto probe the structural and chemical characteristics of low-silica H-FAU zeolites, and distinguish two kinds of protons within supercages based on the band area ratio of OH 3630 /OH 3650 (i.e., OH SII /OH SIII , S II and S III refer to site II and site III in supercages, as shown in Figure 1a infrared spectra acquired upon the adsorption of pyridine.…”