Due to the presence of small structural units (e.g., D4R, D3R), the frameworks of germanosilicate zeolites are generally characterized by high pore volumes and multidimensional/extra-large pore systems, making them especially suitable in processing bulky molecules (in particular, involved in biomass-derived compound valorization). However, the weak acidity, low hydrothermal stability and high cost of Ge significantly limited the practical use of Ge-containing zeolites.
This thesis aimed at design of sustainable germanosilicate zeolite-based catalysts of modifiable chemical composition and tunable porosity for relevant acid-catalyzed reactions, such as ketalization of polyols, epoxidation of olefins, Baeyer-Villiger oxidation of cyclic ketones and Meerwein-Ponndorf-Verley reduction of aldehydes.
Zeolites are crystalline microporous materials with three-dimensional frameworks built from corner-sharing TO4 tetrahedra. Traditionally, zeolites are defined as aluminosilicates (T = Si and Al). Nowadays, the skeleton atoms have been expanded to other tri-/tetra-valent elements, including B, Ga, Ge, Ti, etc., due to the chemical flexibility of zeolites. Resulting materials are termed as elementosilicates for respective element-containing zeolites. Such materials exhibit fascinating properties due to the different nature of elements in the framework, e.g. structural flexibility and tunable acidity. However, the complexity of the factors affecting the zeolite synthesis limits the possibility to control the key parameters of zeolites formation, e.g. crystallization mechanism, crystal growth rate, and phase selectivity. This thesis was focused on the design of a series of elementosilicate zeolites with tunable properties (in particular, morphology, porosity, or acidity) either through controlling the crystallization mechanism or by manipulation with the zeolite structure and chemical composition.
Zeolites are crystalline aluminosilicates and environmentally friendly solid acid catalysts thanks to their non-toxicity, large surface area, excellent (hydro)thermal stability, and tunable acidity. Traditionally, zeolite catalysts are applied in industrial processes related to petrochemistry, but several studies have recently shown their high potential in fine chemicals production and volatile organic compounds (VOCs) elimination. Advanced materials based on newly developed layered and nanosized zeolites have exhibited further fascinating properties, e.g., a short diffusion pathway, tunable structure and morphology. However, the limited correlation between key parameters of zeolite synthesis and their properties (structural, textural, acidic) and catalytic performance, especially for new layered and nanosized zeolites, hinders the development and application of zeolite catalysts.
This thesis was focused on the preparation of several sets of specific zeolite catalysts to gain further insights into the relationship between key properties of zeolites (structure, morphology, chemical composition, accessibility to acid sites or other functional groups, and organization of layers, among others) and their performance as catalysts, supports for other active phases or nanosized components of colloidal system
This PhD thesis focuses on modification of the structure and textural properties of germanosilicates using different ways of post-synthesis treatment: the ADOR (Assembly –Disassembly – Organization – Reassembly) transformation and post-synthesis degermanation and alumination.
Recent research in zeolite science is focused on designing strategies for preparation of
hierarchical micro-mesoporous or micro-macroporous zeolites, with the purpose of replacing
toxic and environmentally unfriendly homogeneous catalysts used for different reactions,
involving bulky reagents and/or products. A one-pot three-component Prins-Friedel-Crafts
reaction of an aldehyde, homoallylic alcohol, and aromatic compound is one of the processes
demanding such intensification for efficient production of valuable heterocyclic compounds
containing the 4-aryltetrahydropyran moiety. This work provides a detailed catalytic
evaluation of specially synthesized Al- and Ga- substituted zeolites with the same topology
but variable crystal morphology to address the acidic and textural characteristics of a
heterogeneous acid catalyst, which are crucial for attaining high activity and selectivity in the
PFC reaction of butyraldehyde, 3-buten-1-ol and anisole.
Controlling both size of metal nanoparticles (MNPs) and acidobasic characteristics of the zeolite support is highly desirable for preparation of stable and active bifunctional catalysts. 2D-3D transformation of layered zeolite precursor into three-dimensional zeolite coupled with metal encapsulation is one of the most efficient synthetic strategies so far to achieve the appropriate metal dispersion and aggregative stability of MNPs within zeolite matrix.
Nevertheless, the effect of support acidic characteristics on the properties of thus prepared metal@zeolite catalyst remained unrevealed, while the synthetic strategy itself requires further optimization to minimize the loss of metal component. This work addresses the influence of chemical composition of zeolite layered precursor on physical-chemical and catalytic properties of metal@zeolite catalysts prepared via 2D-3D transformation strategy, taken Pd@MCM-222D-3D system as a representative example. Both Si/Al ratio of MCM-22P layered precursor (e.g., Si/Al = 15, 20, 30) and Pd loading (e.g., 0.1, 0.3, 0.8 wt.%) were varied resulting in a set of nine Pd@MCM-222D-3D catalysts. In addition, three Pd@MCM-22impreg catalysts with the same metal loading (0.1 wt.%), but different Si/Al ratios of a support were synthesized via conventional impregnation method and used as benchmarking materials. Thus, prepared Pd@MCM-22 catalysts were characterized by various techniques, such as XRD, nitrogen physisorption, electron microscopy, FTIR spectroscopy, while their catalytic performance was tested in hydrogenation of 3-nitrotoluene to 3-aminotoluene.
Available from here.
Recently, post-synthesis degermanation/metallation approach opened the way to zeolite materials with new structures and variable functionalities promising for catalytic applications. However, the influence of the chemical composition of parent germanosilicate on the physicochemical characteristics of thus prepared Al-, Ti-, Sn-substituted zeolites has not been studied yet.
In this work, a series of Al-, Ti- and Sn-substituted zeolites were prepared using degermanation/metallation of IWW and ITH zeolites with variable Si/Ge ratios, while their physicochemical properties were studied using a set of characterization techniques, such as XRD, nitrogen physisorption, ICP-MS, UV-vis spectroscopy, and FTIR spectroscopy of adsorbed probe molecules.
The results of this B.Sc. thesis evidence that a variation in the Si/Ge ratio may result in modification of the crystal size and shape of germanosilicate zeolites and affect the state of metal atoms incorporated into zeolite by a degermanation/metallation approach.
Available from here.