Zeolite UTL Research Articles

Hierarchical Hybrid Organic–Inorganic Materials with Tunable Textural Properties Obtained Using Zeolitic-Layered Precursor

Novel layered zeolitic organic-inorganic materials have been synthesized using a two-dimensional zeolite precursor IPC-1P prepared by a top-down approach from zeolite UTL. The formation of porous materials containing organic linkers or polyhedral oligomeric siloxane covalently bonded to zeolite layers in the interlayer space was confirmed by a variety of characterization techniques (N2/Ar sorption analysis, XRD, (29)Si and (13)C NMR, TEM). The organic-inorganic porous hybrids obtained by intercalation with silsesquioxane posessed layered morphology and contained large crystalline domains. The hybrids exhibited mesoporous or hierarchical micro-/mesoporous systems, stable up to 350 °C. Textural properties of the formed zeolitic organic-inorganic materials can be controlled by varying the linker or synthetic conditions over a broad range. Surface areas and pore volumes of synthesized hybrids significantly exceed those for parent zeolite UTL and corresponding swollen material; the amount of micropores increased with increasing rigidity and size of the organic linker in the order biphenyl > phenylene > ethanediyl.

Extra‐Large‐Pore Zeolites with UTL Topology: Control of the Catalytic Activity by Variation in the Nature of the Active Sites

AbstractThe catalytic behavior of isomorphously substituted B‐, Al‐, Ga‐, and Fe‐containing extra‐large‐pore UTL zeolites was investigated in the acylation of p‐xylene with benzoyl chloride and Beckmann rearrangement of 1‐indanone oxime. The clear synergism between the Brønsted acidity (i.e., the concentration and the strength of protonic acid sites) of UTL catalysts and their activity in benzoylation was established. (Ga)UTL zeolite containing the Brønsted acid sites of medium strength is characterized by the optimum activity and selectivity in the benzoylation of p‐xylene. Because of a higher accessibility of active centers, (Al)UTL zeolite appears to be a more active and selective catalyst than (Al)BEA in the benzoylation of p‐xylene. In contrast to (B), (Ga), and (Al)UTL, the leaching of active sites occurs in the benzoylation over (Fe)UTL. All UTL zeolites showed 100 % selectivity in the Beckmann rearrangement of 1‐indanone oxime, which provides the target 3,4‐dihydroquinolin‐2(1H)‐one. (B) and (Fe)UTL zeolites containing the weakest acid centers were found to be more active in the Beckmann rearrangement of 1‐indanone oxime than (Ga) and (Al)UTL: 100 % yield of the target amide was achieved in 240 min of the reaction time over (B) and (Fe)UTL.

UTL zeolite and the way beyond

Zeolite UTL is the first zeolite synthesized with intersecting 14- and 12-ring channels in the form of germanosilicate. Its framework consists of dense layers supported (‘pillared’) by D4R units enriched in Ge. The synthesis of UTL enabled a new insight into our understanding of zeolite properties, role of different templates, mechanism of zeolite synthesis, and isomorphous substitution. In addition to its attractive properties, zeolite UTL is the first zeolite that has been selectively transformed (dis-assembled) into individual ‘UTL’ layers with preservation of their structure. This disassembly is not only completely new (‘top-down’) approach in the modification of zeolite materials but also enables further manipulation of the layers like swelling, pillaring, and stabilization. This resulted in a new family of UTL-based materials. Upon suitable manipulation, the UTL layers can be condensed to form two new zeolites IPC-2 and IPC-4 (IZA code PCR). These zeolites were synthesized via newly proposed synthetic mechanism ADOR (A – assembly, D – dis-assembly, O – organization, R – re-assembly). The ADOR approach is believed to be a general strategy that will lead to the preparation of new zeolites.

The Effect of Synthesis Conditions and Nature of Heteroelement on Acidic Properties of Isomorphously Substituted UTL Zeolites

The Effect of Synthesis Conditions and Nature of Heteroelement on Acidic Properties of Isomorphously Substituted UTL Zeolites

Catalytic performance of Metal-Organic-Frameworks vs. extra-large pore zeolite UTL in condensation reactions.

Catalytic behavior of isomorphously substituted B-, Al-, Ga-, and Fe-containing extra-large pore UTL zeolites was investigated in Knoevenagel condensation involving aldehydes, Pechmann condensation of 1-naphthol with ethylacetoacetate, and Prins reaction of β-pinene with formaldehyde and compared with large-pore aluminosilicate zeolite beta and representative Metal-Organic-Frameworks Cu3(BTC)2 and Fe(BTC). The yield of the target product over the investigated catalysts in Knoevenagel condensation increases in the following sequence: (Al)beta < (Al)UTL < (Ga)UTL < (Fe)UTL < Fe(BTC) < (B)UTL < Cu3(BTC)2 being mainly related to the improving selectivity with decreasing strength of active sites of the individual catalysts. The catalytic performance of Fe(BTC), containing the highest concentration of Lewis acid sites of the appropriate strength is superior over large-pore zeolite (Al)beta and B-, Al-, Ga-, Fe-substituted extra-large pore zeolites UTL in Prins reaction of β-pinene with formaldehyde and Pechmann condensation of 1-naphthol with ethylacetoacetate.

Transformation of aromatic hydrocarbons over isomorphously substituted UTL: Comparison with large and medium pore zeolites

Isomorphously substituted UTL zeolite with heteroatoms Al, Ga and Fe was synthesized, characterized by X-ray powder diffraction, scanning electron images, nitrogen adsorption isotherms and pyridine adsorption followed by FTIR spectroscopy and tested in disproportionation of toluene, toluene alkylation with isopropyl alcohol and trimethylbenzene disproportionation/isomerization. The catalytic properties of UTL zeolites were compared with those of BEA and MFI zeolites and the observed differences are discussed. Isomorphously substituted (Al, Ga, Fe) UTL zeolites show in most cases lower conversions for the reactions studied but higher selectivities to more valuable products. For toluene disproportionation reaction UTL zeolites shown higher selectivity to xylenes compared with BEA and MFI. In toluene alkylation with isopropyl alcohol no n-propyltoluenes are formed over (Ga)UTL or (Fe)UTL while some traces of this undesired product were observed over (Al)UTL. (Al)UTL shows high selectivity to cymenes and iso-/n-propyltoluene ratio orders of magnitude higher than for MFI. The initial selectivity to xylenes in trimethylbenzene disproportionation/isomerization decreases in the order (Ga)UTL>(Al)UTL≈BEA≫MFI and correlates with increasing of acid centres strength, showing that isomorphously substituted extra-large pore zeolites can be enough active and more selective catalysts in some aromatic hydrocarbon transformation reaction.

Theoretical investigation of layered zeolite frameworks: Interaction between IPC-1P layers derived from zeolite UTL

Interaction between layers of layered zeolite framework IPC-1P was investigated computationally. The inter-layer interaction is controlled by inter-layer hydrogen bonds formed between silanols on adjacent layers. Due to a relatively large concentration of surface silanols in IPC-1P the inter-layer hydrogen bonds account for about 80% of inter-layer interactions. Large number of possible arrangements of neighboring layers exist; the stability of individual arrangements depends primarily on the number of inter-layer hydrogen bonds and their strength. The most stable structure is formed when silanol groups are all parallel with the ac plane and forming a hydrogen-bonded analogue of 10R channel along b direction. Several different arrangements were found with similar interaction energies (within 2.5kJmol−1 per surface silanol). The reliability of computational methods was also investigated. The non-local vdW-DF2 exchange-correlation functional was found to give very accurate description of inter-layer interactions.

Catalytic activity of germanosilicate UTL zeolite in bifunctional hydroisomerisation of n-decane

The factors influencing stability, acidity and catalytic activity of germanosilicate UTL zeolites have been systematically investigated. Three different strategies of bifunctional catalyst preparation were explored. Both X-ray diffraction and 29Si MAS NMR were performed to study structure transformation/degradation of the catalysts. Our results show classical methods of catalysts preparation are not suitable for germanosilicate zeolites which possess low hydrolytic stability and are sensitive to humidity. The present work provides an optimized strategy of catalyst preparation starting from uncalcined UTL zeolite. This method allows to obtain a catalyst stable even after three runs of testing in the n-decane hydroisomerization/hydrocracking reaction.

Synthesis of isomorphously substituted extra-large pore UTL zeolites

The influence of various synthesis parameters (e.g. gel composition, pH of the reaction mixture, duration of crystallization) on the phase selectivity of zeolite formation in germanosilicate reaction medium in the presence of different three-valent heteroatoms (B, Al, Ga, Fe or In) was systematically studied and compared with a controlled crystallization from pure germanosilicate media. The boundary conditions of the formation of the pure phase of isomorphously substituted extra-large pore zeolite UTL were established. In the presence of 1 mol% of the respective heteroelement in the initial gel the pH borders of UTL formation are found to be 7.5–11.9 for Fe-, 7.8–12.0 for B-, 8.2–11.0 for Ga-, 11.0–12.0 for In-, and 11.3–12.0 for Al-containing reaction mixtures. The maximum concentration of heteroelements in the reaction mixture for the successful synthesis of UTL is 1.5 mol% for Al and Ga, 6 mol% for In, and 13 mol% for B. The size of UTL crystals decreases in the order Al- > In- > Ga- > Fe- ≈ B-UTL. The nature of isomorphous substituent influences the textural properties (pore size distribution) of the respective UTL zeolites.

Postsynthesis Transformation of Three-Dimensional Framework into a Lamellar Zeolite with Modifiable Architecture

Mild treatment of zeolite UTL results in degradation of its structure with preservation of the initially present dense layers connected by D4R "bridges". The lamellar product obtained through this 3D to 2D zeolite conversion has been structurally modified similar to methodologies applied to layered zeolite precursors, which show the opposite 2D to 3D zeolite transformation.

Catalytic activity and extra-large pores of germanosilicate UTL zeolite demonstrated with decane test reaction

Pyridine adsorption monitored by FTIR spectroscopy revealed germanosilicate UTL type zeolite to contain intrinsic Bronsted acidity required for catalytic activity. Germanosilicate UTL type zeolite was converted into a bifunctional catalyst and evaluated in n-decane isomerization and hydrocracking. To assess the stability of the framework during catalyst preparation and use, three different strategies of converting the zeolite into bifunctional catalyst were followed: incipient wetness impregnation with Pt(NH3)4Cl2 solution before and after evacuation of the template by calcination, and physical mixing of calcined UTL with Pt-containing amorphous silica. All three samples showed catalytic activity but to very different degrees. The possibility of structure degradation during catalyst preparation and catalysis was investigated by XRD and 29Si MAS NMR. The impregnation of as-made germanosilicate UTL zeolite with platinum and pretreatment in the reactor led to superior stability and activity. The n-decane test previously was used to probe zeolite micropore architectures with 8-, 10- and 12-membered rings. Its validity is now extended to the extra-large pore zeolites. The linear trend of increasing ethyloctanevs.methylnonane selectivity with increasing pore size has now been confirmed also for UTL with 14 membered rings.

Decane Hydroisomerization Test Probing Catalytic Activity and Selectivity of Aluminum and Boron Substituted Extra-Large Pore UTL Zeolite

Extra-large pore germanosilicate zeolite with UTL structure was tested in the n-decane hydroisomerization/hydrocracking reaction. The product selectivity demonstrated UTL to be the most open zeolite material ever characterized with the decane test. Al- and B-containing samples were synthesized with high degree of crystallinity. The incorporation of part of the heteroelements was confirmed with 27Al and 11B NMR spectroscopy. The catalytic activity and the structural stability of these samples was significantly lower compared to germanosilicate UTL and followed the sequence: UTL > Al-UTL > B-UTL.

The Role of Template Structure and Synergism between Inorganic and Organic Structure Directing Agents in the Synthesis of UTL Zeolite

The extra-large-pore germanosilicates with UTL topology have been synthesized using a large variety of spiroazocompounds as structure-directing agents. Synthesis conditions were optimized and zeolites with a high crystallinity degree were obtained with 13 different organic structure-directing agents. The influence of the composition of the reaction mixture and template nature (structure, hydrophilicity/hydrophobicity balance, rigidity, pKa) on the phase selectivity, crystallinity degree, and adsorption properties of zeolites with UTL structure was investigated. Selection criteria of organic molecules as potential structure-directing agents (SDAs) in the synthesis of large-pore and extra-large-pore zeolites from silicate and germanosilicate media are proposed. The optimum synthesis time was determined to be 4−9 days for different SDA and (Si + Ge)/SDA molar ratios. Clear synergism between the optimum structure of organic template and the presence of critical amount of inorganic component (GeO2) was evidenc...

The Role of Crystallization Parameters for the Synthesis of Germanosilicate with UTL Topology

The investigation of the critical synthesis parameters of germanosilicate of UTL topology, possessing 14- and 12-rings, has been carried out in detail. (6R,10S)-6,10-Dimethyl-5-azoniaspiro[4.5]decane hydroxide was used as the structure-directing agent (SDA). The kinetics of the synthesis, the role of the Si/Ge ratio in the synthesis mixture, and the effect of the calcination procedure were investigated in relation to the crystallinity and textural properties of the synthesized material. The optimum synthesis time was found to be six days for Si/Ge and (Si+Ge)/SDA molar ratios of 2 and 1.7, respectively. The UTL zeolite crystallizes as small sheets of 10 mum in size. The micropore volume of the best crystals is 0.22 cm(3) g(-1) with a micropore diameter of 1.05 nm, based on DFT and Saito-Foley analyses of adsorption data.