In-situ ultrasonic monitoring of zeolite A crystallization from coal fly ash

In this study, high phase purity of zeolite A was prepared from coal fly ash precursors. The molar regime of both the clear solution extract and unseparated fly ash slurry was adjusted to achieve the right composition for zeolite A crystallization. The formation process for zeolite A from coal fly ash precursors was monitored in detail using an in situ ultrasonic system and was complemented by use of ex situ techniques such as XRD, FTIR, SEM and FTIR. The findings from both the in situ ultrasonic monitoring process and ex situ techniques clearly contributed significantly in unmasking the formation process of zeolite A from coal fly ash compared to previous studies reported in the literature. The study also enriches the existing body of literature by deeply investigating the gel–solution–crystal interactions starting from this complex feedstock. Comparable ultrasonic signals were generated when both clear and unseparated fly ash based precursor solutions were used during the zeolite synthesis process.Web of Scienc

Immobilization of Aspergillus sp. laccase on hierarchical silica MFI zeolite with embedded macropores

Laccase from Aspergillus sp. (LC) was immobilized on functionalized silica hierarchical (microporous-macroporous) MFI zeolite (ZMFI). The obtained immobilized biocatalyst (LC#ZMFI) was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (ATR-FTIR), N2 adsorption/desorption isotherms, solid-state NMR spectroscopy and thermogravimetric analysis (TGA) confirming the chemical anchoring of the enzyme to the zeolitic support. The optimal pH, kinetic parameters (KM and Vmax), specific activity, as well as both storage and operational stability of LC#ZMFI were determined. The LC#ZMFI KM and Vmax values amount to 10.3 µM and 0.74 µmol·mg-1 min-1, respectively. The dependence of specific activity on the pH for free and immobilized LC was investigated in the pH range of 2-7, The highest specific activity was obtained at pH = 3 for both free LC and LC#ZMFI. LC#ZMFI retained up to 50 % and 30 % of its original activity after storage of 21 and 30 days, respectively. Immobilization of laccase on hierarchical silica MFI zeolite allows to carry out the reaction under acidic pH values without affecting the support structure

Nano-casted N-Doped Carbon Created From a Task-Specific Protic Salt and Controlled Porous Glass

3-dimensionally interconnected macroporous carbons are versatile materials that can be used in catalysis, electrochemical devices, and separation technology. Herein, the synthesis of a nitrogen doped carbonaceous material with a well-defined nanoarchitecture via nano-casting is demonstrated. A novel carbon source, a task-specific protic salt, has been proposed to create nitrogen doped carbon by direct carbonization within the pores of controlled macroporous glass. After the removal of macroporous glass from the composite using an aqueous sodium hydroxide solution and upon further heat treatment, an oxidation resistant doped carbon with high nitrogen content (6 mass %) is obtained. The materials formed during the different stages of the nano-casting process exhibit interesting properties such as hierarchical porosity, very high nitrogen content (15 mass %), and increased oxidational stability. A combination of different properties to create tailor-made materials for different applications using this technique is possible

Synthesis and catalytic properties of hierarchically structured zeolite catalysts with intracrystalline macropores

Zeolites belong to the most important heterogeneous catalysts. They are widely applied in crude oil refining, petrochemistry, fine chemistry, as well as in environmental applications. A unique feature of zeolites is their well-ordered micropore system with pore diameters similar to the dimensions of molecules. These small pores give rise to the shape selective properties of zeolite catalysts. However, the diffusion of molecules to and from the active sites confined within the micropores is very slow, which often leads to diffusion limitations. These diffusion limitations result in reduced utilization of the zeolite crystal and can also lead to reduced selectivity or lifetime of zeolite catalysts. A nature-inspired approach to overcome such diffusion restrictions is the utilization of catalysts with an optimally designed, hierarchical structure. In nature, mass transport systems, such as trees or lungs, possess an optimized hierarchical architecture to reduce transport limitations across a wide range of length scales.1 Adapting this approach to zeolites can be realized by including at least one additional system of larger pores interconnected to the zeolitic micropores. Hereby, hierarchical zeolites coul already demonstrate enhanced diffusion properties and, consequently, better catalytic performance.3 In order to prepare a truly nature inspired catalyst, a guided material design is crucial. Therefore, the transport pore system must exhibit an optimal porosity and the zeolitic domains in between the transport pores need to be small enough to eliminate local diffusion limitations. The pore size can be neglected, if it is larger than a certain minimum pore size, usually in the range of macropores or very large mesopores.3 However, preparation approaches for hierarchical zeolites are often unguided and result mostly in materials containing relative small mesopores. In this contribution we introduce a synthesis approach for zeolite single crystals with intracrystalline macropores by a so-called inverse crystallization, which allows control over the porosity, pore size and wall thickness of the hierarchical zeolite (see Figure 1 b). This synthesis approach utilizes mesoporous spherical silica particles as a sacrificial template for the macropore formation during zeolite synthesis by steam-assisted crystallization. Furthermore, we show the effect of these additional intracrystalline macropores on the catalytic performance for the direct conversion of methanol to short chain olefins (MTO), with focus on coke formation and catalyst lifetime. Please click Additional Files below to see the full abstract

Combined 3D characterization of porous zeolites by STEM and FIB tomography

German Research Foundation Priority Program 1570German Research Foundation Cluster of Excellence EXC 315 “Engineering of Advanced Materials

MFI Type Zeolite Aggregates with Nanosized Particles via a Combination of Spray Drying and Steam-Assisted Crystallization (SAC) Techniques

This article belongs to the Special Issue Catalysis on Zeolites and Zeolite-Like Materials II

Organic-free synthesis of layer-like FAU-type zeolites

The formation of layer-like FAU-type zeolites was facilitated in the absence of any organic template. Instead, the addition of simple inorganic salts turned out to be an effective and easy to handle alternative to organic additives to induce morphological and even structural changes during zeolite crystallisation