Synthesis and Catalytic Application of Macroscopic Zeolite Beads with Hierarchical Porosity

The thesis has been focused on synthesis and catalytic application of macroscopic and hierarchical zeolite beads using hard templating techniques. The hierarchical porosity containing larger meso- and macropores are useful to decrease the diffusion limitation which is a drawback of inherently microporous zeolites. These structured zeolites were used as heterogeneous catalysts in several reactions such as acylation, acetalization, biobased up-grading and epoxidation reactions

A Review on the Effects of Organic Structure-Directing Agents on the Hydrothermal Synthesis and Physicochemical Properties of Zeolites

The study on the synthesis of zeolites, including both the development of novel techniques of synthesis and the discovery of new zeolitic frameworks, has a background of several decades. In this context, the application of organic structure-directing agents (SDAs) is one of the key factors having an important role in the formation of porous zeolitic networks as well as the crystallization process of zeolites. There are various elements that are needed to be explored for elucidating the effects of organic SDAs on the final physicochemical properties of zeolites. Although SDAs were firstly used as pore generators in the synthesis of high-silica zeolites, further studies proved their multiple roles during the synthesis of zeolites, such as their influences on the crystallization evolution of zeolite, the size of the crystal and the chemical composition, which is beyond their porogen properties. The aim of this mini review is to present and briefly summarize these features as well as the advances in the synthesis of new SDAs during the last decades

Efficient and Easily Reusable Metal-Free Heterogeneous Catalyst Beads for the Conversion of CO2 into Cyclic Carbonates in the Presence of Water as Hydrogen-Bond Donor

Two porous Amberlite resin beads consisting of ammonium-functionalized polystyrene cross-linked with divinylbenzene were demonstrated to be efficient, easily recyclable, and viable metal-free heterogeneous catalysts for the reaction of CO2 with epoxides to yield cyclic carbonates. The catalysts were prepared from two affordable, commercially available resin beads, which differ in the nature of their functional groups, i.e., trimethylammonium chloride or dimethylethanolammonium chloride. These materials were converted through a straightforward ion-exchange step into their iodide counterparts (Amb-I-900 and Amb-OH-I-910). The ion-exchanged resin beads were tested as heterogeneous catalysts for the reaction of CO2 with styrene oxide at different reaction conditions (45-150 °C, 2-60 bar of CO2, 3-18 h). The effect of the presence of water as a hydrogen-bond donor in combination with a heterogeneous catalyst was systematically investigated here for the first time. With both catalysts, the presence of water led to higher yields of cyclic carbonate (from 12% to 58% with Amb-I-900 and from 59% to 66% with Amb-OH-I-910; ≥98% selectivity). The highest catalytic activity was observed with Amb-OH-I-910, due to the presence of -OH groups in its active site, which together with water enhanced the activity through hydrogen-bonding interactions. This catalytic system attained higher turnover numbers and turnover frequencies (TON = 505, TOF = 168 for reaction at 150 °C) and improved cyclic carbonate productivity compared to the state-of-the-art supported polymeric bead catalysts and was active in catalyzing the synthesis of styrene carbonate also at low temperature (33% yield at 45 °C and 10 bar of CO2). Additionally, the Amb-OH-I-910 proved to be a versatile catalyst for the conversion of a variety of epoxides into their corresponding cyclic carbonates with good to excellent yields and very high selectivity (≥98%). The two polymeric bead catalysts could be easily recovered and reused without significant loss in their activity and thus represent an easily accessible, environmentally friendly, cost-effective catalytic system for the synthesis of cyclic carbonates from CO2

Bimetallic Zeolite Beta Beads with Hierarchical Porosity as Brønsted-Lewis Solid Acid Catalysts for the Synthesis of Methyl Lactate

Bimetallic zeolite Beta in bead format and containing Al sites with Brønsted acid behavior and Sn, Zr or Hf sites with Lewis acid character, were prepared using a two-step synthetic route. First, zeolite Beta in the format of macroscopic beads (400 to 840 μm) with hierarchical porosity (micropores accessed through meso- and macropores in the range of 30 to 150 nm) were synthesized by hydrothermal crystallization in the presence of anion-exchange resin beads as hard template and further converted into their H-form. Next, the zeolite beads were partially dealuminated using different concentrations of HNO3 (i.e., 1.8 or 7.2 M), followed by grafting with one of the above-mentioned metals (Sn, Zr or Hf) to introduce Lewis acid sites. These bimetallic zeolites were tested as heterogeneous catalysts in the conversion of dihydroxyacetone (DHA) to methyl lactate (ML). The Sn-containing zeolite Beta beads treated by 1.8 M HNO3 and grafted with 27 mmol of SnCl4 (Sn-deAl-1.8-Beta-B) demonstrated the best catalytic activity among the prepared bimetallic zeolite beads, with 99% selectivity and 90% yield of ML after 6 h at 90 °C. This catalyst was also tested in combination with Au-Pd nanoparticles supported on functionalized carbon nanotubes (CNTs) as multifunctional catalytic system for the conversion of glycerol to ML, achieving 29% conversion of glycerol and 67% selectivity towards ML after 4.5 h at 140 °C under 30 bar air. The catalytic results were rationalized by means of a thorough characterization of the zeolitic beads with a combination of techniques (XRD, N2-physisorption, SEM, XRF, TEM, UV-vis spectroscopy and pyridine-FT-IR)

A Comparative Review of Binder-Containing Extrusion and Alternative Shaping Techniques for Structuring of Zeolites into Different Geometrical Bodies

Zeolites are crystalline metallosilicates displaying unique physicochemical properties with widespread applications in catalysis, adsorption, and separation. They are generally obtained by a multi-step process that starts with primary mixture aging, followed by hydrothermal crystallization, washing, drying, and, finally, a calcination step. However, the zeolites obtained are in the powder form and because of generating a pressure drop in industrial fixed bed reactors, not applicable for industrial purposes. To overcome such drawbacks, zeolites are shaped into appropriate geometries and desired size (a few centimeters) using extrusion, where zeolite powders are mixed with binders (e.g., mineral clays or inorganic oxides). The presence of binders provides good mechanical strength against crushing in shaped zeolites, but binders may have adverse impacts on zeolite catalytic and sorption properties, such as active site dilution and pore blockage. The latter is more pronounced when the binder has a smaller particle size, which makes the zeolite internal active sites mainly inaccessible. In addition to the shaping requirements, a hierarchical structure with different levels of porosity (micro-, meso-, and macropores) and an interconnected network are essential to decrease the diffusion limitation inside the zeolite micropores as well as to increase the mass transfer because of the presence of larger auxiliary pores. Thus, the generation of hierarchical structure and its preservation during the shaping step is of great importance. The aim of this review is to provide a comprehensive survey and detailed overview on the binder-containing extrusion technique compared to alternative shaping technologies with improved mass transfer properties. An emphasis is allocated to those techniques that have been less discussed in detail in the literature.</p

Binder-free zeolite Beta beads with hierarchical porosity:Synthesis and application as heterogeneous catalysts for anisole acylation

Three zeolites (H-Beta, H-ZSM-5 and H-Y) were synthesized in the form of binder-free macroscopic beads (350-800 µm) using a hydrothermal method employing anion-exchange resin beads as hard template. The beads obtained after removal of the hard template by calcination consisted of crystalline zeolite domains connected with each other to form a hierarchical porous network in which the zeolitic micropores are accessible through meso- and macropores, as proven by characterization with XRD, N2 physisorption, SEM, and TEM. The composition, the nature and amount of acid sites and the degree of hydrophobicity of these beads were investigated by means of XRF, solid-state NMR, pyridine-FTIR and TGA. The zeolite beads were tested as heterogeneous catalysts in the Friedel-Crafts acylation of anisole with acetic anhydride to produce para-methoxyacetophenone. H-Beta-Beads displayed the best catalytic performance with 95% conversion of acetic anhydride and 76% yield of para-methoxyacetophenone in a batch reactor test (90 °C, 6 h). Next, the catalytic performance of H-Beta-Beads was compared in both batch and continuous-flow mode to extrudates prepared by mixing zeolite Beta powder with either kaolin or bentonite binders. H-Beta-Beads outperformed the extrudates in batch-mode reactions and could be reused in multiple runs without discernible loss of activity. In the continuous-flow test, H-Beta-Beads demonstrated higher average activity but deactivated more rapidly than the extrudates

Synergistic Catalytic Effects of Alloys of Noble Metal Nanoparticles Supported on Two Different Supports:Crystalline Zeolite Sn-Beta and Carbon Nanotubes for Glycerol Conversion to Methyl Lactate

Two multifunctional catalytic systems comprising Sn-based/doped crystalline zeolite Beta were synthesized, and they were employed as heterogeneous catalysts in the selective conversion of glycerol to methyl lactate. The first catalytic system, named Au-Pd-Sn-deAl-7.2-Beta-DP, was created through the post-synthesis dealumination of the parent zeolite Beta (Si/Al = 10) using 7.2 M HNO3. Subsequently, it was grafted with 27 mmol of SnCl4, resulting in Sn-deAl-7.2-Beta. Following this, Au and Pd nanoparticles were supported on this catalyst using the deposition–precipitation (DP) method. The second catalytic system was a physical mixture of Au and Pd nanoparticles supported on functionalized carbon nanotubes (Au-Pd-F-CNTs) and Sn-containing zeolite Beta (Sn-deAl-7.2-Beta). Both catalytic systems were employed in glycerol partial oxidation to methyl lactate under the following conditions: 140 °C for 4.5 h under an air pressure of 30 bar. The Au-Pd-Sn-deAl-7.2-Beta-DP catalytic system demonstrated 34% conversion of glycerol with a 76% selectivity for methyl lactate. In contrast, the physical mixture of Au-Pd-F-CNTs and Sn-deAl-7.2-Beta exhibited higher activity, achieving 58% glycerol conversion and a nearly identical selectivity for methyl lactate (77%). The catalytic results and catalyst structure were further analyzed using various characterization techniques, such as X-ray diffraction (XRD), N2 physisorption, scanning electron microscopy (SEM), X-ray fluorescence (XRF), transmission electron microscopy (TEM), UV-vis spectroscopy, and pyridine Fourier transform infrared (FTIR). These analyses emphasized the significance of adjusting the quantity of active sites, particle size, and active sites proximity under the chosen reaction conditions.</p

Synergistic Catalytic Effects of Alloys of Noble Metal Nanoparticles Supported on Two Different Supports:Crystalline Zeolite Sn-Beta and Carbon Nanotubes for Glycerol Conversion to Methyl Lactate

Two multifunctional catalytic systems comprising Sn-based/doped crystalline zeolite Beta were synthesized, and they were employed as heterogeneous catalysts in the selective conversion of glycerol to methyl lactate. The first catalytic system, named Au-Pd-Sn-deAl-7.2-Beta-DP, was created through the post-synthesis dealumination of the parent zeolite Beta (Si/Al = 10) using 7.2 M HNO3. Subsequently, it was grafted with 27 mmol of SnCl4, resulting in Sn-deAl-7.2-Beta. Following this, Au and Pd nanoparticles were supported on this catalyst using the deposition–precipitation (DP) method. The second catalytic system was a physical mixture of Au and Pd nanoparticles supported on functionalized carbon nanotubes (Au-Pd-F-CNTs) and Sn-containing zeolite Beta (Sn-deAl-7.2-Beta). Both catalytic systems were employed in glycerol partial oxidation to methyl lactate under the following conditions: 140 °C for 4.5 h under an air pressure of 30 bar. The Au-Pd-Sn-deAl-7.2-Beta-DP catalytic system demonstrated 34% conversion of glycerol with a 76% selectivity for methyl lactate. In contrast, the physical mixture of Au-Pd-F-CNTs and Sn-deAl-7.2-Beta exhibited higher activity, achieving 58% glycerol conversion and a nearly identical selectivity for methyl lactate (77%). The catalytic results and catalyst structure were further analyzed using various characterization techniques, such as X-ray diffraction (XRD), N2 physisorption, scanning electron microscopy (SEM), X-ray fluorescence (XRF), transmission electron microscopy (TEM), UV-vis spectroscopy, and pyridine Fourier transform infrared (FTIR). These analyses emphasized the significance of adjusting the quantity of active sites, particle size, and active sites proximity under the chosen reaction conditions.</p