Ring Zeolites Research Articles

Selectivity Descriptors of Methanol-to-Aromatics Process over 3-Dimensional Zeolites.

The zeolite-catalyzed methanol-to-aromatics (MTA) process is a promising avenue for industrial decarbonization. This process predominantly utilizes 3-dimensional 10-member ring (10-MR) zeolites like ZSM-5 and ZSM-11, chosen for their confinement effect essential for aromatization. Current research mainly focuses on enhancing selectivity and mitigating catalyst deactivation by modulating zeolites' physicochemical properties. Despite the potential, the MTA technology is at a low Technology Readiness Level, hindered by mechanistic complexities in achieving the desired selectivity towards liquid aromatics. To bridge this knowledge gap, this study proposes a roadmap for MTA catalysis by strategically combining controlled catalytic experiments with advanced characterization methods (including operando conditions and "mobility-dependent" solid-state NMR spectroscopy). It identifies the descriptor-role of Koch-carbonylated intermediates, longer-chain hydrocarbons, and the zeolites' intersectional cavities in yielding preferential liquid aromatics selectivity. Understanding these selectivity descriptors and architectural impacts is vital, potentially advancing other zeolite-catalyzed emerging technologies.

Selectivity Descriptors of Methanol‐to‐Aromatics Process over 3‐Dimensional Zeolites

AbstractThe zeolite‐catalyzed methanol‐to‐aromatics (MTA) process is a promising avenue for industrial decarbonization. This process predominantly utilizes 3‐dimensional 10‐member ring (10‐MR) zeolites like ZSM‐5 and ZSM‐11, chosen for their confinement effect essential for aromatization. Current research mainly focuses on enhancing selectivity and mitigating catalyst deactivation by modulating zeolites′ physicochemical properties. Despite the potential, the MTA technology is at a low Technology Readiness Level, hindered by mechanistic complexities in achieving the desired selectivity towards liquid aromatics. To bridge this knowledge gap, this study proposes a roadmap for MTA catalysis by strategically combining controlled catalytic experiments with advanced characterization methods (including operando conditions and “mobility‐dependent” solid‐state NMR spectroscopy). It identifies the descriptor‐role of Koch‐carbonylated intermediates, longer‐chain hydrocarbons, and the zeolites′ intersectional cavities in yielding preferential liquid aromatics selectivity. Understanding these selectivity descriptors and architectural impacts is vital, potentially advancing other zeolite‐catalyzed emerging technologies.

Shape selection of alkane hydroisomerization over one-dimensional zeolite supported Pt catalyst: Pt/ZSM-48 versus Pt/ZSM-22

Hydroisomerization of long-chain n-alkanes plays a vital role in petrochemical and coal chemical industries, because it can produce high-quality hydrocarbon fuels and lubricant base oils. ZSM-48 (0.56 × 0.53 nm) and ZSM-22 (0.57 nm × 0.46 nm) are characteristic of one-dimensional 10-member ring zeolites suitable for n-alkanes hydroisomerization reaction. Here, the effect of the structure difference between ZSM-48 and ZSM-22 zeolites on hydroisomerization is titrated by the isobutane and n-dodecane. The product distribution of hydroisomerization of isobutane to n-butane shows the reaction pathway on Pt/ZSM-48 and Pt/ZSM-22, in which the monomolecular hydroisomerization of isobutane is involved within the active sites in zeolite channels, while the polymerization-cracking bimolecular reaction occurs on the pore-mouth of zeolite. Pt/ZSM-48 zeolite, possessing larger channel and aperture size than those of Pt/ZSM-22, is more conducive to the diffusion of butane molecules and bimolecular polymerization. Therefore, the isobutane conversion (14 %) on Pt/ZSM-48 produces less C1+C2 (1.7 wt% vs. 3.4 wt%) and more C3+C5+C8 (19.2 wt% vs. 16.9 wt%). For the hydroisomerization of n-dodecane, the iso-dodecane selectivity of Pt/ZSM-48 (43.3 wt%) is significantly higher than that of Pt/ZSM-22 (12.4 wt%) at the similar n-C12 conversion (40 %). Compare with the isomers of Pt/ZSM-22, the mono-branched isomers with methyl near the middle of the chains and multi-branched isomers are more easily formed on Pt/ZSM-48, which is conducive to the “key-lock” catalysis mechanism. The larger pore size of ZSM-48 is conducive to n-C12 insertion into zeolite pores, methyl migration and isomer diffusion, and its adjacent pores are more compatible with double-branched isomers. In addition, a high selectivity of C4∼C5 alkanes (53.2 wt%) on Pt/ZSM-22 and a high selectivity of C6∼C9 alkanes (44.7 wt%) on Pt/ZSM-48 show obvious difference in cracking product distribution, implying different position of methyl groups in i-C12 isomers on Pt/ZSM-22 and Pt/ZSM-48 samples, respectively. The present comparison between Pt/ZSM-48 and Pt/ZSM-22 benefits the selection and development of one-dimensional zeolitesupported metal catalyst in a wide range of hydro-processing reactions.

Comparative study of Pt/zeolites for n-hexadecane hydroisomerization: EU-1, ZSM-48, ZSM-23, ZSM-22, and ZSM-12

The hydroisomerization of n-hexadecane was investigated using bifunctional platinum catalysts supported on EU-1, ZSM-48, ZSM-23, ZSM-22, and ZSM-12 zeolites. These one-dimensional microporous zeolites were synthesized at 160 ℃ with an Si/Al molar ratio of 60, and 0.5 wt% Pt was loaded onto them using the impregnation method. The findings indicate that Brønsted acidity predominantly influences the conversion to n-hexadecane over 10 membered ring zeolites. Additionally, ZSM-12, characterized by a 12-ring channel, exhibits preferential activity in this regard. The apparent activation energy for the reactions increased from 81 kJ/mol (Pt/ZSM-23) to 134 kJ/mol (Pt/ZSM-48) across all tested catalysts. Pt/ZSM-22 demonstrated high selectivity towards mono-branched isomers, whereas Pt/ZSM-12 favored the formation of multi-branched isomers. The isomer selectivity trend was Pt/ZSM-22 > Pt/ZSM-12 > Pt/EU-1 > Pt/ZSM-48 > Pt/ZSM-23. Moreover, TG analysis of spent catalysts unveiled that coke formation on these zeolites was chiefly influenced by zeolite channel structure and Brønsted acid content. The average coke selectivity followed this order: Pt/EU-1 > Pt/ZSM-12 > Pt/ZSM-48 > Pt/ZSM-22 > Pt/ZSM-23.

Selectivity descriptors of the catalytic n-hexane cracking process over 10-membered ring zeolites.

Zeolite-mediated catalytic cracking of alkanes is pivotal in the petrochemical and refining industry, breaking down heavier hydrocarbon feedstocks into fuels and chemicals. Its relevance also extends to emerging technologies such as biomass and plastic valorization. Zeolite catalysts, with shape selectivity and selective adsorption capabilities, enhance efficiency and sustainability due to their well-defined network of pores, dimensionality, cages/cavities, and channels. This study focuses on the alkane cracking over 10-membered ring (10-MR) zeolites under industrially relevant conditions. Through a series of characterizations, including operando UV-vis spectroscopy and solid-state NMR spectroscopy, we intend to address mechanistic debates about the alkane cracking mechanism, aiming to understand the dependence of product selectivity on zeolite topologies. The findings highlight topology-dependent mechanisms, particularly the role of intersectional void spaces in zeolite ZSM-5, influencing aromatic-based product selectivity. This work provides a unique understanding of zeolite-catalyzed hydrocarbon conversion, linking alkane activation steps to the traditional hydrocarbon pool mechanism, contributing to the fundamental knowledge of this crucial industrial process.

Modification of Zeolite Morphology via NH4F Etching for Catalytic Bioalcohol Conversion

AbstractVarious commercial zeolites, including FER, MOR, ZSM‐5, BEA, and FAU frameworks, were treated with NH4F aqueous solutions to study the effects of fluoride etching on different zeolite frameworks. NH4F‐treated small‐medium pore FER, MOR, and ZSM‐5 samples showed much higher mesoporosities than the untreated ones without alteration of the structural compositions and acidic properties. On the other hand, the 12‐membered ring zeolites BEA and FAU showed severe dissolution of the framework aluminosilicate structure after NH4F etching due to the high accessibility of fluoride species into the framework structures. The effect of NH4F concentration on the fluoride treatment of H‐ZSM‐5 zeolite was specifically studied. From the results, we observed that structural etching with 20 wt % NH4F was optimal for fabricating open‐pore H‐ZSM‐5 zeolite and resulted in a high mesoporosity with comparable relative crystallinity and acidity with respect to the untreated H‐ZSM‐5. The catalytic activities of the open‐pore H‐ZSM‐5 were evaluated with acid‐catalyzed methanol and bioethanol conversions. Remarkably, the hierarchical open‐pore H‐ZSM‐5 zeolite fabricated via fluoride etching exhibited an enhanced catalytic performance in bioethanol conversion with >85 % conversion over 34 h TOS and a higher catalytic stability in methanol conversion than the parent H‐ZSM‐5 (~50 % of bioethanol conversion at 34 h TOS).

Hierarchical zeolites TNU-9 and IM-5 as the catalysts for cracking processes

The 10-ring zeolites TNU-9 and IM-5 were obtained by a desilication and evaluated in series of acid-catalysed cracking reactions. n-Decane and 1,3,5-tri-iso-propylbenzene cracking were performed as model reactions, while vacuum gas oil, polypropylene and polyethylene were cracked into add-value lower molecular weight chemicals. The catalytic performance improvement of hierarchical zeolites was rationalized by deep acid sites characterization in situ FT-IR studies of pyridine, carbon monoxide and 2,6-di-tert-butylpyridine sorption. Further, operando FT-IR-GC studies supported by 2D COS (two-dimensional correlation) analysis provided insight into cracking and coking of catalysts during polypropylene and polyethylene decomposition. It was found that NaOH-derived catalysts ensure the most upsurged acidity, in terms of number and accessibility of the sites, and then with better performance. In VGO cracking the connected mesopores added post-synthesis increased yields to propylene and middle distillates and lowered coke production. A bigger share of iso-olefins was observed both in VGO and polyolefins cracking products.

Mercaptoamine‐assisted Post‐encapsulation of Metal Nanoparticles within Preformed Zeolites and their Analogues for Hydroisomerization and Methane Decomposition

AbstractWe report a general synthetic strategy for post‐encapsulation of metal nanoparticles within preformed zeolites using post‐synthetic modification. Both anionic and cationic precursors to metal nanoparticle are supported on 8‐ and 10‐membered ring zeolites and analogues during wet impregnation using 2‐aminoethanethiol (AET) as a bi‐grafting agent. Thiol groups are coordinated to metal centers, whereas amine moieties are dynamically attached to micropore walls via acid‐base interactions. The dynamic acid‐base interactions cause the even distribution of the metal‐AET complex throughout the zeolite matrix. These processes encapsulate Au, Rh, and Ni precursors within the CHA, *MRE, MFI zeolite, and SAPO‐34 zeolite analogues, for which small channel apertures preclude the post‐synthesis impregnation of metal precursors. Sequential activation forms small and uniform nanoparticles (1–2.5 nm in diameter), as confirmed through electron microscopy and X‐ray absorption spectroscopy. Containment within the small micropores protected the nanoparticles against harsh thermal sintering conditions and prevented the fouling of the metal surface by coke, thus resulting in a high catalytic performance in n‐dodecane hydroisomerization and methane decomposition. The remarkable specificity of the thiol to metal precursors and the dynamic acid‐base interaction make these protocols extendable to various metal‐zeolite systems, suitable for shape‐selective catalysts in challenging chemical environments.

Mercaptoamine-assisted Post-encapsulation of Metal Nanoparticles within Preformed Zeolites and their Analogues for Hydroisomerization and Methane Decomposition.

We report a general synthetic strategy for post-encapsulation of metal nanoparticles within preformed zeolites using post-synthetic modification. Both anionic and cationic precursors to metal nanoparticle are supported on 8- and 10-membered ring zeolites and analogues during wet impregnation using 2-aminoethanethiol (AET) as a bi-grafting agent. Thiol groups are coordinated to metal centers, whereas amine moieties are dynamically attached to micropore walls via acid-base interactions. The dynamic acid-base interactions cause the even distribution of the metal-AET complex throughout the zeolite matrix. These processes encapsulate Au, Rh, and Ni precursors within the CHA, *MRE, MFI zeolite, and SAPO-34 zeolite analogues, for which small channel apertures preclude the post-synthesis impregnation of metal precursors. Sequential activation forms small and uniform nanoparticles (1-2.5 nm in diameter), as confirmed through electron microscopy and X-ray absorption spectroscopy. Containment within the small micropores protected the nanoparticles against harsh thermal sintering conditions and prevented the fouling of the metal surface by coke, thus resulting in a high catalytic performance in n-dodecane hydroisomerization and methane decomposition. The remarkable specificity of the thiol to metal precursors and the dynamic acid-base interaction make these protocols extendable to various metal-zeolite systems, suitable for shape-selective catalysts in challenging chemical environments.

Butane Hydroisomerisation Using Pt‐Promoted OSDA‐Free Zeolite Beta

AbstractHydroisomerisation of n‐butane to isobutane is a challenging reaction, even for Pt‐loaded zeolites with strong acid sites. In comparison with 10‐membered ring (10MR) zeolites, 12‐membered ring (12MR) zeolites give consistently higher isomerisation yields. We report that besides the known catalysts with *BEA topology, also three‐dimensional frameworks with MSE and YFI topologies (with Si/Al∼10) are suitable to obtain high isobutane selectivities and yields. As an alternative to Beta zeolites obtained via templated synthesis, Beta zeolites prepared via a template‐free synthesis proved to be more active at lower temperatures and delivered higher isobutane yields in such conditions. Side reactions such as the Pt‐catalysed hydrogenolysis were successfully suppressed by decreasing the Pt content, even in hydrogen‐rich conditions. Isobutane yields up to 31 % were achieved in a single pass.

SAPO-35 zeolite crystallized using novel structure-directing agent for catalytic conversion of levulinic acid into ethyl levulinate under non-microwave instant heating

SAPO-35 zeolite (LEV topology) is an 8-membered ring zeolite material that offers high selectivity and activity in separation and catalysis but this microporous material can only be crystallized using hexamethyleneimine, quinuclidine and cyclohexylamine organic templates thus far. Herein, the hydrothermal synthesis and crystallization evolution of SAPO-35 using a novel N-heterocyclic organic template, namely 1-propylpyridinium hydroxide ([PPy]OH), are reported. As compared to the previous reported hexamethyleneimine-templated synthesis conditions (24 h, 200 °C), the current system requires merely 21 h to fully crystallize SAPO-35 using [PPy]OH new template. Furthermore, the current system also witnesses a different route for crystallizing SAPO-35 where dissolution of reactants (induction), nucleation, crystal growth and intrazeolite transformation from SAPO-34 to SAPO-35 are observed. The resulting SAPO-35 zeolite of high porosity and acidity is active and selective in the catalytic conversion of levulinic acid into ethyl levulinate―a biofuel additive―under non-microwave instant heating, where it shows 96.3% conversion and 100% selectivity towards ethyl levulinate after 20 min at 190 °C with high catalyst reusability. Hence, this work offers a promising route to crystallize SAPO-35 that is benign for catalytic biofuel upgrading.

Acidic property of YNU-5 zeolite influenced by its unique micropore system

YNU-5 zeolite has the YFI -type framework with a 12-12-8-ring system (2-dimensional 12-oxygen membered ring pores 3-dimensionally connected by twin 8-ring channels), and isolated 8-ring channels separated from the system by a thin (mono-atomic silicate) wall. In this study, the acidic property of YNU-5 zeolite was analyzed mainly by means of the ammonia IRMS-TPD (infrared/mass spectroscopy temperature-programmed desorption) method. In addition, the accessibility of acid sites was evaluated through adsorption of pyridine. The number of Brønsted acid sites approximately agreed with the number of Al atoms, and the amount of Lewis acid sites was negligible, indicating that most acid sites have the nature of bridging Si(OH)Al group in the YFI framework. Most of the Brønsted acidic OH groups on the YNU-5 zeolites (including the dealuminated samples) reacted with pyridine vapor at 343 K to form pyridinium cations, indicating that the Brønsted acid sites are highly accessible through the 12-12-8-ring system. Enthalpy of ammonia desorption from the Brønsted acid site, which can be an index of acid strength or reactivity of the acid site with a basic reactant, was in the following order: FAU < MOR (12-ring) ≈ *BEA < MFI < MWW ≈ YFI < MOR (8-ring), indicating the markedly large ammonia desorption enthalpy on the YNU-5 zeolite compared to the other 12-ring zeolites. The DFT calculations suggest that the Brønsted acidic protons with especially high ammonia desorption enthalpy are located in the isolated 8-ring but accessible from the 12-12-8-ring system side. In addition, dealumination at a high temperature under the reflux conditions with nitric acid resulted in the preferential removal of Brønsted acid sites with low ammonia desorption enthalpy, probably in the 12-12-8-ring system. The presence of reactive Brønsted acid sites in the isolated 8-ring, accessibility to them from the 12-12-8-ring system, and preferential removal of the Brønsted acid sites from the 12-12-8-ring system are reasonably consistent with the previously reported catalytic properties for dimethyl ether-to-olefin reaction. • Enthalpy of ammonia desorption (Δ H ) from the Brønsted acid site on the YNU-5 zeolite was high. • The Brønsted acidic protons with high Δ H were located in the isolated 8-ring but accessible from the 12-12-8-ring system. • Dealumination in the reflux conditions of nitric acid preferential proceeded in the 12-12-8-ring system.

Reaction pathways of n-butane cracking over the MFI, FER and TON zeolites: Influence of regional differences in Brønsted acid sites

Three zeolites ZSM-5, ZSM-35 and ZSM-22 are applied in n -butane cracking to reveal the influence of regional differences in Brønsted acid sites on reaction pathways. The Brønsted acid sites located in the channels of ZSM-5 exhibit a higher catalytic activity and yields to light olefins (especially the ethylene), which can be attributed to more relative contribution of bimolecular pathway. In comparison, more Brønsted acid sites are situated on the external surface or micropore mouths of ZSM-35 and ZSM-22, which are beneficial to propylene production. Note-worthily, almost no propane production on the two zeolites implies the predomination of monomolecular pathway. In situ FTIR technique further discloses that the difference in the reaction pathways is tailored by adsorption configurations of n -butane at two types of Brønsted acid sites. Under comparable conditions, the ZSM-5 performs a relatively good catalytic stability through bimolecular pathway. Furthermore, the correlation between deactivation rate and light olefins reveals that the enhancement of propylene selectivity accelerates the deactivation of ZSM-35 and ZSM-22. While, promotion on the ethylene selectivity is a significant inducement for the deactivation of ZSM-5. Reaction pathways of n-butane cracking tailored by the influence of regional differences in Brønsted acid sites. • Three typical 10-member ring zeolites ZSM-5, ZSM-35 and ZSM-22 are prepared. • Reaction pathways of n -butane cracking over the zeolites are investigated. • Regional differences in Brønsted acid sites tailor the selectivities to propylene and ethylene. • ZSM-5 zeolite exhibits high catalytic activity and stability compared to ZSM-35 and ZSM-22. • Catalyst deactivation mechanisms are revealed on different reaction pathways.

Unveiling the elusive role of tetraethyl orthosilicate hydrolysis in ionic-liquid-templated zeolite synthesis

Despite previous reports showing that crystallization kinetics affects zeolite phase selectivity because zeolites are metastable species in their synthesis solution rather than thermodynamic end points, the critical kinetics-controlling parameter is yet to be determined. This work elucidated the effect of tetraethyl orthosilicate (TEOS) hydrolysis before hydrothermal treatment on the final zeolite phase selectivity in the ionic liquid-templated synthesis of 10-membered ring zeolites (MFI- or TON-type zeolites). The results showed that the dissolved silica concentration in the synthesis solution, which is controlled by varying the TEOS hydrolysis temperature and addition rate, induced heterogeneous nuclear growth. Specifically, in 1-butyl-3-methylimidazolium ([BMIM]Br)-directed syntheses, the high and low concentrations of dissolved silica species led to MFI and TON zeolite formation, respectively. The experimental results are supported by silica polymerization modeling using the Reaction Ensemble Monte Carlo method and theoretical calculations on composite building unit formation. The results are valuable for understanding the nucleation mechanism in zeolite crystallization.

Study on the Synthesis of Chabazite Zeolites via Interzeolite Conversion of Faujasites.

The interzeolite conversion of faujasite (FAU-type) zeolites to chabazite (CHA-type) zeolite in the presence of N,N,N-trimethyladamantammonium and N,N,N-dimethylethylcyclohexylammonium cations was investigated over a large compositional range by carefully controlling the reaction mixture compositions. Highly crystalline CHA zeolites were also obtained by the transformation of several zeolite types including EMT, LTL, LEV, RTH, and MFI frameworks. The formation of CHA zeolite from FAU zeolite precursors was substantially faster than that from zeolite L with a similar composition. High-silica CHA zeolites were also produced successfully using a mixture of TMAda with a number of less expensive organic structure-directing agents. The CHA zeolite materials have been synthesized with high crystallinity and with a Si/Al ratio ranging from 5 to 140. Our data support the importance of structural similarity between the zeolite precursors, nucleation/crystallization processes, and the zeolite product in the interzeolite conversion compared to conventional amorphous aluminosilicate gels. Our synthetic methods could be used to prepare other 8-membered ring zeolites such as AEI and AFX frameworks, potential candidates for selective catalytic reduction of NOx, light olefin production, and CO2 abatement.

Catalysts and shape selective catalysis in the methanol-to-olefin (MTO) reaction

Recent advances in the shape selectivity of zeolites and molecular sieve catalysts for the methanol-to-olefins (MTO) reaction are elaborated in this minireview. The concept and classification of shape selectivity are briefly introduced and summarized. The effect of cavity structure of cavity-type zeolites and molecular sieves are comprehensively discussed, with focus on the formation of hydrocarbon pool intermediates, reaction route, diffusion, product selectivity, as well as deactivation in the chemical environment of cavity-type molecular sieves. Furthermore, the impact of topology of zeolites and molecular sieves on reaction route and product selectivity are elucidated, with special attention on the shape selectivity of 1-dimensional 10-membered ring zeolites. The debate regarding the impact of coke formation on product selectivity over SAPO-34 is also discussed in detail. Moreover, the progress of modification strategies including metal cations incorporation and pre-coking process for improving shape selectivity have been summarized. The perspective of shape selective catalysis in future is outlined and predicted.

Preparation of extra-large micropore Sn-zeolites and their catalytic performance in Baeyer–Villiger oxidations

A series of extra-large micropore Sn-zeolites with different Si/Sn ratios is post-synthesized by treating the interlayer-expanded material ECNU-9-cal773 with a solution of HCl containing NH4F and SnCl4∙5H2O, named as IEZ-Sn-PLS-3(S4R). During treatment, HCl, NH4F, and SnCl4∙5H2O are hydrolyzed into H+, F+, and Sn4+ ions. The formation of a small amount of HF formed from H+ and F+ ions can corrode the Si atom of the zeolite sheets and generate hydroxy-nest defect sites, Sn4+ ions fill up the hydroxy-nests to form isolated framework Sn active sites. The structure and active sites of the obtained materials are studied by various characterization methods. IEZ-Sn-PLS-3(S4R) possesses a 14 × 12-ring (R) pore system and framework Sn active sites. With enlarged pore sizes, IEZ-Sn-PLS-3(S4R) has been proved to be efficient for catalyzing the Baeyer–Villiger oxidation of 2-admantanone using H2O2 as the oxidant. The low Si/Sn sample resulted in a higher conversion compared to typical 12-ring zeolite Sn-Beta hydrothermally synthesized in an F− system.

State of the Art and Perspectives of Hierarchical Zeolites: Practical Overview of Synthesis Methods and Use in Catalysis.

Microporous zeolites have proven to be of great importance in many chemical processes. Yet, they often suffer from diffusion limitations causing inefficient use of the available catalytically active sites. To address this problem, hierarchical zeolites have been developed, which extensively improve the catalytic performance. There is a multitude of recent literature describing synthesis of and catalysis with these hierarchical zeolites. This review attempts to organize and overview this literature (of the last 5 years), with emphasis on the most important advances with regard to synthesis and application of such zeolites. Special attention is paid to the most common and important 10- and 12-membered ring zeolites (MTT, TON, FER, MFI, MOR, FAU, and *BEA). In contrast to previous reviews, the research per zeolite topology is brought together and discussed here. This allows the reader to instantly find the best synthesis method in accordance to the desired zeolite properties. A summarizing graph is made available to enable the reader to select suitable synthesis procedures based on zeolite acidity and mesoporosity, the two most important tunable properties.

Dehydration of 1,3-butanediol to butadiene over medium-pore zeolites: Another example of reaction intermediate shape selectivity

Here we compare the catalytic properties of the proton form of 11 medium-pore zeolites, with different framework topologies and/or compositions for the dehydration of biomass-derived 1,3-butanediol at 300 °C under excess water conditions (H2O/1,3-butanediol = 45). It was found that high-silica H-ferrierite (Si/Al = 130) with intersecting 10- and 8-ring channels exhibits the highest butadiene yield, together with the best durability, among the zeolites tested. Due to its highly inactive nature, however, 3-buten-1-ol, one of the butenol reaction intermediates in 1,3-butanediol dehydration, also remained a major by-product. IR spectroscopy with adsorbed 3-buten-1-ol shows that intramolecularly hydrogen-bonded 3-buten-1-ol exists predominantly in H-ZSM-5 with two intersecting 10-ring channels, while the one with no intramolecular hydrogen bonding is another species found not only in H-ferrierite but also in the one-dimensional 10-ring zeolite H-ZSM-22. By combining both experimental and theoretical results, we conclude that 1,3-butanediol dehydration over medium-pore zeolites may constitute another example of reaction intermediate shape selectivity.

Synthesis of 10 and 12 Ring Zeolites (MCM-22, TNU-9 and MCM-68) Modified with Zn and Its Potential Application in the Reaction of Methanol to Light Aromatics and Olefins

The effect on the incorporation of zinc of three zeolites TNU-9, MCM-22, and MCM-68 was investigated. The physico-chemical properties of zeolites were studied by X‐ray diffraction, N2-adsorption, temperature‐programmed desorption of NH3 (TPD), nuclear magnetic resonance of 27Al and 29Si (MAS NMR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Then all the samples were characterized and evaluated in the reaction of methanol to aromatics (MTA). The correlation of zinc incorporation method and acidic properties of zeolites with catalytic performance was investigated. The form of zinc incorporation, the acidity, the type of zeolitic structure and the reaction temperature had a great influence on the catalytic activity. Regarding the type of structure, the total aromatics selectivity in this work increased in the followed order for zeolites modified with Zn: MCM-68 > TNU-15 > MCM-22. The medium pore zeolite T9-15 (TNU-9 zeolite and Si/Al 15 ratio) catalysts with the ratio ZnO/ZnO + Al2O3 equal to 0.34 (T9-15 0.5 Zn) showed better stability with conversion of methanol completes during 9 h of reaction and 17% to BTX selectivity and 32% to total aromatics compounds at 450 °C and WHSV of 4.24 h−1. In methanol conversion, the selectivity to aromatics over the T9-15 modified-Zn materials (TNU-9 zeolite and Si/Al 15 ratio) under study, increased in the followed order: T9-15 0.5 Zn > ZT9-15 > T9-15 > T9-15 0.2 Zn. The reaction temperature is an important variable in the MTA process. At 450 °C a better activation of acid sites is achieved in zeolite with Zn and therefore a high percentage of BTX selectivity is obtained for TNU-9 zeolite.