Organic-Free, ZnO-Assisted Synthesis of Zeolite FAU with Tunable SiO2 /Al2 O3 Molar Ratio

Heteroatom Manipulation of Zeolite Crystallization: Stabilizing Zn-FAU against Interzeolite Transformation

The preparation of metastable zeolites is often restricted to a limited range of synthesis conditions, which is exemplified in commercial syntheses lacking organics to stabilize the crystal structure. In the absence of an organic structure-directing agent, interzeolite transformation is a common phenomenon that can lead to undesirable products or impurities. Many studies have investigated the substitution of Si and Al in zeolite frameworks with alternative elements (heteroatoms) as a means of tailoring the properties of zeolites; however, relatively few studies have systematically explored the impact of heteroatoms on interzeolite transformations and their concomitant effects on zeolite crystallization. In this study, we examine methods to prepare isostructures of faujasite (FAU), which is one of the most commercially relevant zeolites and also a thermodynamically metastable structure. A survey of multivalent elements revealed that zinc is capable of stabilizing FAU at high temperatures and inhibiting its frequent transformation to zeolite gismondine (GIS). Using combined experimental and computational studies, we show that zinc alters the chemical nature of growth mixtures by sequestering silicates. Zinc heteroatoms incorporate in the FAU framework with a loading-dependent coordination. Our collective findings provide an improved understanding of driving forces for the FAU-to-GIS interzeolite transformation where we observe that heteroatoms (e.g., zinc) can stabilize zeolite FAU over a broad range of synthesis conditions. Given the growing interest in heteroatom-substituted zeolites, this approach to preparing zinc-containing FAU may prove applicable to a broader range of zeolite structures.

Synthesis of mesoporous ZnO/TiO2-SiO2 composite material and its application in photocatalytic adsorption desulfurization without the addition of an extra oxidant

Photocatalytic adsorption desulfurization (PADS) technology has attracted enormous attention in the deep desulfurization field. Therefore, a good material with high photocatalytic activity and adsorption capacity toward organic sulfide is desirable. Herein, mesoporous ZnO/TiO2-SiO2 (ZTS) was synthesized for the first time and successfully applied in the photocatalytic desulfurization of dibenzothiophene (DBT). The composite materials were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), N2-physisorption, transmission electron microscopy (TEM), UV-Vis diffusive reflectance spectra (UV-Vis DRS), X-ray photo-electron spectroscopy (XPS), photoluminescence (PL) and electron spin resonance (ESR). The results show that the doping of TiO2 promotes the photocatalytic and adsorption abilities of the catalysts dramatically. ZTS-3 with Si/Ti = 3 exhibits the best photocatalytic desulfurization activity compared with other proportions of titanium doping. The final DBT conversion can reach 97%, and the maximum adsorption of DBT over ZTS-3 is 47 mg-S per g-cat. The photocatalytic test indicates that the remarkable photocatalytic activity of ZTS is due to the formation of a heterojunction by the interaction of ZnO and TiO2, which can successfully expand solar light absorption, improving the charge separation efficiency and inhibiting the recombination of photocatalytic electron-hole pairs. Moreover, no extra oxidants (such as O2, H2O2 or an organic oxidant) were added, which is highly beneficial for the consequent treatment of the fuel and can reduce the processing cost markedly.