Silicalite-1 Zeogrid: A New Silica Molecular Sieve with Super- and Ultra-Micropores

Abstract

Spherical, micrometer‐sized particles with a layered structure were obtained by precipitation of a Silicalite‐1 zeolite nanoslab suspension upon addition of cetyltrimethylammonium bromide (CTMABr) and subsequent calcination. The material had a specific micropore volume of 0.69 cm3 g–1, distributed over super‐ and ultra‐micropores. The formation process of this peculiar microporous solid was studied using X‐ray diffraction (XRD), 29Si MAS NMR spectroscopy, thermogravimetry (TG), and nitrogen adsorption. In the precipitate, the Silicalite‐1 nanoslabs were laterally fused into nanoplates and stapled into layers with intercalated surfactant molecules. Removal of the surfactant through calcination caused facial fusion, besides additional lateral fusion, of the nanoplates. Empty spaces left lying laterally between individual nanoplates were responsible for the super‐microporosity. The ultra‐micropores were zeolitic channels inside the fused nanoplates. The potential of these Silicalite‐1 zeogrids as molecular sieves was demonstrated with pulse gas‐chromatographic separation of alkane mixtures. The mass‐transfer resistance of a packed bed of zeogrid particles was considerably lower than of compacted zeolite powder.

Synthesis and characterization of Pd/ZSM-5/MCM-48 biporous catalysts with superior activity for benzene oxidation

“…Over the last couple of years, several simple and reliable approaches have been developed to form micro/mesoporous combined materials using zeolite nanoparticles or zeolite seeds as the silica source [31][32][33][34][35][36]. However, most of the published reports on composite catalysts have focused on one-dimensional materials (such as MCM-41 or SBA-15) as the mesostructured component, although three-dimensional materials, such as cubic MCM-48, are more interesting from the viewpoint of catalysis due to the interwoven pore system, which allows the sufficient diffusion of reactants within the pores, subsequently leading to a better catalytic performance [37].…”

“…However, M41S materials generally exhibit weak acidity and low hydrothermal stability due to their amorphous frameworks. As a consequence, new synthesis strategies have been developed to obtain materials which com-bine the advantages of mesoporous materials and those of zeolites [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. For example, Corma et al [21] reported a post-synthesis dealumination process via steaming or acid leaching on full-grown zeolites.…”

Synthesis and characterization of zeogrid molecular sieves

“…The presence of a dual microporosity, viz. a combination of ultra-and super-micropores was evidenced with nitrogen adsorption isotherms at 77 K [17]. Zeogrid exhibits molecular shape selectivity in chromatographic separations of mixtures of branched and linear alkanes [17].…”

“…Empty spaces left laterally between nanoslabs are responsible for the formation of well-defined slit-shaped super-micropores, with a characteristic height of ca. 1.4 nm [17]. The presence of a dual microporosity, viz.…”

“…Zeolite micropores are conventionally designated as ultra-micropores with pore widths smaller than 1 nm, to be distinguished from super-micropores with diameters from 1 to 2 nm. An ultra-microporesuper-micropore combination can be realized in Zeogrid materials [17,18]. Zeogrid is obtained through precipitation of a suspension of Silicalite-1 nanoslabs [19,20] upon addition of an ethanolic solution of cetyltrimethylammonium bromide (CTMABr).…”