Germanosilicate Zeolite Research Articles

Ni-Supported Germanosilicate Zeolite SCM-14 for Efficient Hydrogenolysis of 5-Hydroxymethylfurfural to 2,5-Dimethylfuran

Ni-Supported Germanosilicate Zeolite SCM-14 for Efficient Hydrogenolysis of 5-Hydroxymethylfurfural to 2,5-Dimethylfuran

Realizing the Direct Synthesis of High Silica IWS Zeolite with Improved Hydrothermal Stability.

Direct synthesis of germanosilicate zeolites with low Ge content and improved hydrothermal stability is a great challenge. Herein, we successfully achieve the direct synthesis of IWS zeolite with a Si/Ge ratio higher than 4 for the first time. High silica IWS zeolites can be prepared in a wide range of Si/Ge ratios (4-16) by utilizing bulky 1,3-bis(1-adamantyl)-imidazolium (BAdaI+) as an efficient organic structure-directing agent from the concentrated synthesis gel under fluoride conditions. It is proven by a series of characterizations that Ge atoms preferentially occupy the double-four-ring (D4R) units. Theoretical calculations reveal the preferential interactions of guest organic structure-directing agents (OSDAs) and host IWS zeolites with different Si/Ge ratios. The introduction of more Ge atoms cannot improve the host-guest interaction when the BAdaI+ molecule is accommodated within the nanopores of IWS zeolite compared to other OSDAs. The obtained IWS zeolite shows an extremely high specific surface area (905 m2/g) and pore volume (1.31 cm3/g). Due to the low Ge content, IWS zeolite exhibits outstanding hydrothermal stability and experiences high temperature steam heating with no loss of crystallinity and only a slight loss of microporosity.

Zeolite-catalyzed one-pot sucrose-to-HMF transformation: Ge outperforms Sn, Zr, and Al sites

The conversion of renewable compounds to versatile platform molecules over environmentally friendly heterogeneous catalysts is a major challenge. Zeolites stand as active, selective, and reusable solid catalysts for various acid-catalyzed reactions involved in the one-pot cascade transformation of polysaccharides to 5-hydroxymethylfurfural (HMF), a platform molecule opening the way to various valuable chemicals. However, the acidity-performance relationships of zeolite catalysts in HMF synthesis have not been fully elucidated. Here, we have addressed the effect of acid site nature in zeolite catalysts for sucrose-to-HMF transformation by comparing the performance of conventional Al-substituted IWW zeolite with that of Sn-, Zr-, and Ge-containing zeolite catalysts of the same structure. Ge-associated acid sites were found to exhibit superior HMF selectivity compared to Sn, Zr, and Al acid centers, while experiencing evolution into Brønsted acid centers during the catalytic run. The conversion of sucrose over germanosilicate zeolites enhances with increasing catalyst pore diameter or decreasing crystal size. Specifically, the extra-large pore Ge-UTL catalyst, featuring intersecting 14- and 12-ring pores (crystal size 10 × 20 × <1 μm), and large-pore Ge-IWW with 12-, 10- and 8-ring pores (crystal sizes of 1 μm) showed a yield of targeted HMF comparable to or even exceeding the values previously reported for homogeneous or heterogeneous catalysis (54 % after 3 h at 120 °C). Ge-IWW catalyst demonstrated reusability across a minimum of 3 catalytic runs, while in situ structural transformation precluded stable performance of Ge-UTL catalyst in the repetitive catalytic cycles. The results of this study highlight zeolites with uncharacteristic chemical compositions as active, selective, and reusable catalysts for highly demanding applications in biomass valorization.

Mechanism of the Low-Temperature Organic Removal from Imidazolium-Containing Zeolites by Ozone Treatment: Fluoride Retention in Double-4-Rings.

For zeolites synthesized using imidazolium cations, the organic matter can be extracted at very low temperatures (100 °C) using ozone. This is possible for zeolites with 12-ring or larger pores but requires higher temperatures in medium-pore zeolites. The first chemical events in this process occur fast, even at room temperature, and imply the loss of aromaticity likely by the formation of an adduct between ozone and the imidazole ring through carbons C4 and C5. Subsequent rupture of the imidazole ring provides smaller and more flexible fragments that can desorb more readily. This process has been studied experimentally, mainly through infrared spectroscopy, and theoretically by density functional theory. Amazingly, fluoride anions occluded in the small double-four-ring units (d4r) during the synthesis remain inside the cage throughout the whole process when the temperature is not too high (≤150 °C). However, fluoride in larger cages in MFI ends up bonded to silicon in penta or hexacoordinated units, likely out of the cages, after ozone treatment at 150 °C. For several germanosilicate zeolites, the process allows their subsequent degermanation to yield stable high-silica zeolites. Quaternary ammonium cations require harsher conditions that eventually also extract fluoride from zeolite cages, including the d4r unit.

Balancing Ge de-intercalation and Si re-insertion rates stabilizes hydrolytically labile germanosilicate zeolites

Germanosilicate zeolites are attractive adsorbents and catalysts thanks to their diverse structures and versatile textural properties. However, hydrolytic instability of such zeolites, even under ambient conditions, restricts their practical applications....

Design of an Organic Template for Synthesizing ITR Zeolites under Ge-Free Conditions.

Germanosilicate zeolites with various structures have been extensively synthesized, but the syntheses of corresponding zeolite structures in the absence of germanium species remain a challenge. One such example is an ITR zeolite structure, which is a twin of the ITH zeolite structure. Through the modification of a classic organic template for synthesizing ITH zeolites and thus designing a new organic template with high compatibility to ITR zeolite assisted by theoretical simulation, we, for the first time, show the Ge-free synthesis of an ITR structure including pure silica, aluminosilicate, and borosilicate ITR zeolites. These materials have high crystallinity, corresponding to an ITR content of more than 95%. In the methanol-to-propylene (MTP) reaction, the obtained aluminosilicate ITR zeolite exhibits excellent propylene selectivity and a long lifetime compared with conventional aluminosilicate ZSM-5 zeolite. The strategy for the design of organic templates might offer a new opportunity for rational syntheses of novel zeolites and, thus, the development of highly efficient zeolite catalysts in the future.

Tailored alkyl-imidazolium templating synthesis of extra-large-pore germanosilicate zeolite ITT as Baeyer-Villiger oxidation catalyst

Extra-large-pore germanosilicate zeolite ITT was prepared with several structure-tailored alkyl-substituted imidazolium templates. The effect of alkyl chain length and substitution number of template on zeolite topology structure was studied with the variation of synthesis Si/Ge ratio. 1-hexyl-3-methyl-imidazaolium (1H3M) exhibited superior templating effect on the formation of ITT structure within the widest range of synthesis Si/Ge molar ratio of about 2–6. 1H→13C CP/MAS NMR, TGA and molecular simulation results revealed that two 1H3M was occluded in the 18-ring channels per unit cell, presenting the lowest interaction energy with framework. With the combination of XRD, SEM, EDS, ICP, 29Si, 19F MAS NMR, FTIR, N2 physisorption results, it was found that the increase of synthesis Si/Ge ratio improved framework Si/Ge ratio within d4r unit to a certain degree, and in the meantime resulted in the decrease of zeolite crystallinity with the formation of some amorphous phase. ITT showed better Lewis-acid catalytic activity and lactone selectivity for B–V oxidation of 2-adamantanone than BEC, the best germanosilicate zeolite ever reported. The excellent catalytic performance was ascribed to the presence of 18-ring channels in ITT, which facilitated the diffusion of bulky ketone substrate and lactone product. The structure stability of ITT during the reaction was evaluated with the use of either aqueous H2O2 or non-aqueous tert-butyl hydroperoxide (TBHP) as oxidant.

Synthesis and Characterization of A Stable Extra-Large-Pore Zeolite with 15×12×12 Member-Ring Channels.

Extra-large-pore zeolites have great application potential in various industrial fields, such as oil refinery, fine chemicals and biomass processing. Herein, we report the synthesis of an extra-large-pore germanosilicate zeolite (named NUD-13) by using an easily obtained aromatic organic cation 1,2-dimethyl-3-propyl-benzimidazolium as organic structure-directing agents. NUD-13 possesses a rare 15-member ring extra-large-pore channel intersecting with two elliptical 12-member ring channels, which is isostructural to germanosilicate zeolite GeZA synthesized by using triphenylsulfonium. The germanium in NUD-13 can be partially substituted by acid treatment to obtain stable high silica zeolite. In addition, aluminium is added into the framework of NUD-13 during the post-synthesis treatment process, which provides a foundation for catalytic application.

Direct synthesis of aluminosilicate ITH zeolite in the presence of a small organic template

Despite very successful synthesis of many pure silica or germanosilicate zeolites, there are still challenges for direct synthesis of their aluminosilicate forms. As a typical example, it is easy to synthesize germanosilicate ITH, but difficult for direct synthesis of its aluminosilicate form. Recently, cationic oligomer has been successfully templated for direct formation of aluminosilicate ITH, but relatively complex steps for controlling molecular weight of the cationic oligomer strongly hinder the practical production of zeolite products. Herein, it is shown an alternative route for direct synthesis of aluminosilicate ITH zeolite in the presence of a small organic template with both structural directing ability for the ITH structure and strong interaction ability to aluminum species. Characterizations of the zeolite products with Si/Al ratios from 46 to 148 show high crystallinity, nanosheet-like crystal morphology, large microporous surface area (338 m2/g), high micropore volume (0.16 cm3/g), four-coordinated Al species, controllable acidic sites, and extraordinary hydrothermal stability (hydrothermal aging at 800 °C for 5 h with 10% water steaming). Catalytic tests in methanol-to-propylene (MTP) show that the aluminosilicate ITH zeolite has higher selectivity for propylene than that of commercial ZSM-5 zeolite with similar Si/Al ratio, which provides a candidate catalyst for MTP reaction in the near future.

Synthesis and structure of the medium-pore zeolite PST-35 with two interconnected cages of unusual orthorhombic shape.

The search for new zeolite structures and compositions remains important in synthetic materials science due to the high impact on developing new chemical technologies, as well as on improving existing ones. Herein we present the synthesis and structure of PST-35, a novel medium-pore germanosilicate (Si/Ge = 2.1–6.6) zeolite, achieved by combining the excess fluoride approach and the unique structure directing ability of Ge in the presence of 1,2,3-triethylimidazolium ions as an organic structure-directing agent. PST-35 contains a zig-zag 10-ring (4.6 × 6.7 Å) channel system constructed of strictly alternating large 28-hedral ([48·58·68·82·102]) and smaller 18-hedral ([46·54·64·82·102]) cages of anomalous orthorhombic shape. The PST-35 structure is built from the connection of pst-35 layers consisting of small 8-hedral ([43·54·6]) cages, previously unobserved zeolite building layers, through single 4-rings.

Tailored Alkyl-Imidazolium Templating Synthesis of Extra-Large-Pore Germanosilicate Zeolite Itt as Baeyer-Villiger Oxidation Catalyst

Tailored Alkyl-Imidazolium Templating Synthesis of Extra-Large-Pore Germanosilicate Zeolite Itt as Baeyer-Villiger Oxidation Catalyst

In situ synchrotron X-ray diffraction reveals the disassembly–organisation mechanism of germanosilicate zeolites in HCl vapour

In situ synchrotron X-ray diffraction technique was applied for germanosilicate zeolites to study the disassembly–organisation mechanism of ADOR in HCl vapour, in which three steps are involved.

HPM‐16, a Stable Interrupted Zeolite with a Multidimensional Mixed Medium–Large Pore System Containing Supercages

AbstractHPM‐16 is a highly porous germanosilicate zeolite with an interrupted framework that contains a three‐dimensional system of 12+10×10(12)×12+10‐membered ring (MR) pores. The 10(12) MR pore in the b direction is a 10 MR pore with long 12 MR stretches forming 30 Å long tubular supercages. Along one direction the 10 MR pores are fused, meaning that the separation between adjacent pores consists of a single tetrahedron that is, additionally, connected to only three additional tetrahedra (a Q3). These fused pores are thus decorated by T‐OH groups along the whole diffusion path, creating a hydrophilic region embedded in an otherwise essentially hydrophobic environment. The structure is built from highly porous 12×12×12 MR uninterrupted layers that are connected to each other through Q3 producing a second system of 10×10×10 MR pores. This zeolite can be extensively degermanated yielding a material with high thermal stability, despite its interrupted nature.

Toward Controlling Disassembly Step within the ADOR Process for the Synthesis of Zeolites

The application of the Assembly–Disassembly–Organization–Reassembly (ADOR) protocol to the synthesis of germanosilicate zeolites has become a major milestone in material design by enabling the prep...

Reverse ADOR: reconstruction of UTL zeolite from layered IPC-1P.

The assembly–disassembly–organisation–reassembly (ADOR) process has led to the discovery of numerous zeolite structures, albeit limited to materials with decreased pore size in relation to the parent germanosilicate zeolite. This limitation stems from the rapid decrease in d-spacing upon hydrolysis (disassembly). Nevertheless, we have artificially increased the d-spacing of layered IPC-1P by intercalating organic species. Furthermore, we have reconstructed double four rings (D4R) between layers, thus transforming IPC-1P back into the parent UTL zeolite. This reconstruction has provided not only germanosilicate but also a new, high-silica UTL zeolite (Si/Ge = 481). Therefore, our “reverse ADOR” opens up new synthetic routes towards promising extra-large-pore zeolite-based materials with new chemical compositions.

HPM-14: A New Germanosilicate Zeolite with Interconnected Extra-Large Pores Plus Odd-Membered and Small Pores*.

HPM-14 is a new extra-large pore zeolite synthesized using imidazolium-based organic structure-directing agents (SDAs), fluoride anions, and germanium and silicon as tetrahedral components of the framework. Owing to the presence of stacking disorder, the structure elucidation of HPM-14 was challenging, and different techniques were necessary to clarify the details of the structure and to understand the nature of the disorder. The structure has been solved by three-dimensional electron-diffraction technique (3D ED) and consists of an intergrowth of two polymorphs possessing a three-dimensional channel system, including an extra-large pore opened through windows made up of sixteen tetrahedral atoms (16-membered ring, 16MR) as well as two additional sets of odd-membered (9MR) and small (8MR) pores. The intergrowth has been studied by scanning transmission electron microscopy (Cs -STEM) and powder X-ray diffraction simulations (DIFFaX), which show a large predominance of the monoclinic polymorph A.

HPM‐14: A New Germanosilicate Zeolite with Interconnected Extra‐Large Pores Plus Odd‐Membered and Small Pores**

AbstractHPM‐14 is a new extra‐large pore zeolite synthesized using imidazolium‐based organic structure‐directing agents (SDAs), fluoride anions, and germanium and silicon as tetrahedral components of the framework. Owing to the presence of stacking disorder, the structure elucidation of HPM‐14 was challenging, and different techniques were necessary to clarify the details of the structure and to understand the nature of the disorder. The structure has been solved by three‐dimensional electron‐diffraction technique (3D ED) and consists of an intergrowth of two polymorphs possessing a three‐dimensional channel system, including an extra‐large pore opened through windows made up of sixteen tetrahedral atoms (16‐membered ring, 16MR) as well as two additional sets of odd‐membered (9MR) and small (8MR) pores. The intergrowth has been studied by scanning transmission electron microscopy (Cs‐STEM) and powder X‐ray diffraction simulations (DIFFaX), which show a large predominance of the monoclinic polymorph A.

Synthesis of BEC-type germanosilicates with asymmetric diquaternary ammonium salts

This paper deals with the synthesis of germanosilicate zeolites using asymmetric diquaternary ammonium salts as organic structure-directing agents (OSDA). Seven pyrrolidinium and piperidinium derivatives were chosen, with different carbon chain lengths and different terminal groups linked to the nitrogen atoms. For each OSDA, the syntheses were performed with four different gel compositions, i.e. in fluoride or hydroxide media both in concentrated or diluted conditions. The products were identified using powder X-ray diffraction data (PXRD). The integrity of the structure-directing agents were verified using 13C liquid and solid-state NMR spectroscopy and thermogravimetric analyses. For one sample, the Rietveld method allowed us to localize the OSDA inside the pore and the fluoride ions inside the d4r composite building unit but, also inside the main 12-ring channels as proved by 19F solid-state NMR spectroscopy.

Synthesis and Post-Synthesis Transformation of Germanosilicate Zeolites.

Zeolites are one of the most important heterogeneous catalysts, with a high number of large-scale industrial applications. While the synthesis of new zeolites remain rather limited, introduction of germanium has substantially increased our ability to not only direct the synthesis of zeolites but also to convert them into new materials post-synthetically. The smaller Ge-O-Ge angles (vs. Si-O-Si) and lability of the Ge-O bonds in aqueous solutions account for this behaviour. This Minireview discusses critical aspects of germanosilicate synthesis and their post-synthesis transformations to porous materials.

Synthesis and Post‐Synthesis Transformation of Germanosilicate Zeolites

AbstractZeolites are one of the most important heterogeneous catalysts, with a high number of large‐scale industrial applications. While the synthesis of new zeolites remain rather limited, introduction of germanium has substantially increased our ability to not only direct the synthesis of zeolites but also to convert them into new materials post‐synthetically. The smaller Ge‐O‐Ge angles (vs. Si‐O‐Si) and lability of the Ge−O bonds in aqueous solutions account for this behaviour. This Minireview discusses critical aspects of germanosilicate synthesis and their post‐synthesis transformations to porous materials.