10-membered Ring Channels Research Articles

Unlocking Enhanced Butadiene Selectivity: The Crucial Role of Zeolite Channel Confinement in the Selective Decarbonylation of γ-Valerolactone.

Herein, we report a highly selective production route for butadiene from γ-valerolactone over zeolite catalysts. The catalytic performance of eight zeolites with different framework topologies were compared, revealing that zeolites with narrower 10-membered ring channels exhibit enhanced selectivity of butadiene. Specifically, ZSM-35 and ZSM-22, featuring the narrowest 10-membered ring channels, demonstrate the highest butadiene selectivity to 61 % and 59 %, respectively. Notably, surface passivation of ZSM-35 leads to a remarkable increase in butadiene selectivity to 82 %, maintaining a 99 % conversion. Additionally, we propose a reaction network and identify cyclopentenone as a key intermediate in the transformation of γ-valerolactone to butadiene. Both experimental and theoretical results conclude that confinement effect of 10-membered ring channels improves the selectivity of butadiene.

Hierarchical beta zeolites assisted aromatics production from lignin via catalytic fast pyrolysis

Converting lignin waste into aromatics is a challenging but crucial aspect of lignin valorization. Although ZSM-5 zeolite is extensively used in lignin deoxygenation, its 10-membered ring (MR) channels limit the diffusion of bulky phenols and tend to produce coke. Herein, a series of 12-MR beta zeolites with varying acidity and hierarchical porosity were synthesized for lignin catalytic fast pyrolysis (CFP). An optimal lignin pyrolysis temperature of 600 °C was initially selected. Subsequently, lignin CFP demonstrated that beta zeolite with medium acidity facilitated aromatics production, with Beta(36) even outperforming ZSM-5(36). The introduction of mesopores further enhanced lignin deoxygenation and the hierarchical B36-0.3-24 increased aromatics selectivity to 56.0 area%, which was 1.5 times that of Beta(36). Combined with the CFP of model compounds (vanillin and catechol), it was inferred that the mesopores and weak acidity played a key role in heavy phenols conversion and aromatics production. In addition, B36-0.3-24 exhibited outstanding reusability in pyrolysis regeneration cycles, underscoring its potential for practical application in lignin valorization.

Boron-incorporated nanosized SUZ-4 zeolite for DME carbonylation.

Boron-incorporated nanosized HB-SUZ-4 showcased a noteworthy 24% boost in dimethyl ether carbonylation, with an elevation in methyl acetate selectivity from 91.8% to 96.0%. The improved performance is attributed to shortened diffusion lengths along the 8-member ring channels, decreased Brønsted acidity in the 10-member ring channels, and Lewis acid sites stabilizing CO.

Nonionic polymer and amino acid-assisted synthesis of ZSM-5 nanocrystals and their catalytic application in the alkylation of 2-methylnaphthalene.

The synthesis of nanosized ZSM-5 zeolites with high crystallinity and suitable acidity is very significant for their great potential in various catalytic applications. Herein, a series of zeolite ZSM-5 crystals with different particle sizes and SiO2/Al2O3 ratios (10-30) were synthesized by a temperature-varying two-step crystallization method in a concentrated gel system containing L-lysine and/or polyvinylpyrrolidone (PVP) additives. By optimizing the addition amounts of the two additives, the crystal size of the ZSM-5 zeolite could be reduced to less than 100 nm. Meanwhile, relatively high crystallinity and framework Al incorporation rates could be achieved, resulting in the generation of high-quality ZSM-5 nanocrystals. The nanosized H-form ZSM-5 zeolite with a SiO2/Al2O3 ratio of 20 showed enhanced catalytic efficiency and stability for the alkylation of 2-methylnaphthalene (2-MN) with methanol to produce an important intermediate, 2,6-dimethylnaphthalene (2,6-DMN). A relatively high and steady yield of 2,6-DMN (above 7.2%) could be achieved during 20 h time-on-stream at 400 °C. The smaller crystal size, higher crystallinity and framework Al content could provide more accessible Brønsted acid sites in the 10-membered ring channel of the ZSM-5 nanocrystals, which are the main active sites responsible for the shape-selectivity of the targeted product of 2,6-DMN. As a result, the formation of other side products like 1-MN and poly-MN could be effectively inhibited, thus leading to an improved 2,6-DMN yield and coke resistance over the nanosized ZSM-5 catalyst.

Use of Borosilicate Seeds to Synthesize Aluminosilicate SSZ-82, a Zeolite Containing Intersecting 12- and 10-Membered Ring Channels

Use of Borosilicate Seeds to Synthesize Aluminosilicate SSZ-82, a Zeolite Containing Intersecting 12- and 10-Membered Ring Channels

Insight into performance over IM-5, ZSM-5 and ZSM-11 zeolites for n-heptane cracking to light olefins in the absence & presence of steam

The three dimension (3D) 10-membered ring channels zeolite has a unique advantage in increasing light olefins for catalytic cracking reaction. Herein, zeolites IM-5, ZSM-5 and ZSM-11 were synthesized hydrothermally to achieve comparable texture properties and SiO2/Al2O3 ratios. The acid content and acid strength of the three zeolites were as follows: IM-5 > ZSM-5 > ZSM-11. Meanwhile, 1H DQ MAS NMR confirmed that there was a synergistic effect between Brønsted and Lewis acids in IM-5 zeolite. However, IM-5 zeolite with lots of strong BAS had an unexpected low TOF in n-heptane cracking. Furthermore, the light olefins selectivity was as follows: IM-5 > ZSM-11 > ZSM-5 at 550–650 ℃ in the absence of steam. IM-5 zeolite had the particular advantage in ethylene, and its selectivity was up to 44.9 %. After steam was introduced, the monomolecular cracking reaction, the aromatization of propylene and the deep cracking of C3 and C4 hydrocarbons were inhibited over the three zeolites. Steam could prolong the activity of IM-5 zeolite, but accelerate the deactivation of ZSM-5 and ZSM-11 zeolites. The primary cause for the rapid deactivation of ZSM-5 and ZSM-11 zeolites was dealuminization in steam, whereas for the IM-5 zeolite, it was the rapid formation of coke on its surface, thereby blocking its micropore channels.

Aldol condensation of biomass-derived aldehydes and ketones followed by hydrogenation over Ni/HZSM-5 to produce aviation fuel: Role of acid sites

As the aviation sector grows and fossil fuels are utilized, the environment and economy depend on biomass-based aviation fuel. This study investigated acid sites in aldol condensation to produce aviation fuel from biomass-derived aldehydes and ketones over the bifunctional catalyst Ni/HZSM-5. Due to its excellent 10-member ring channels structure, HZSM-5 yielded 63.81% of the targeted condensates as aviation fuel precursor. At 200 °C for 9 h, aldehydes and ketones were converted to 90.32% and 69.53% of the required condensates. Sodium ion-exchange HZSM-5 with different Brönsted acid site quantities was tested for condensation. Brönsted acid sites were the active center for aldol condensation of aldehydes and ketones, increasing product yield. In γ-Al2O3, the overall amount of Brönsted acid and Lewis acid was equivalent to that of HZSM-5, the amount of Lewis acid was much more. The yield of the targeted condensates over γ-Al2O3 was only 46.11%, much lower than that of HZSM-5 (69.53%). Thus, Brönsted acid sites were better than Lewis acid sites for aldol condensation of aldehydes and ketones. The balance of active sites for aldol condensation and hydrogenation increased the intended alkane yield to 62.91% with 20 wt% Ni loading. This study involves improving biomass-based aviation fuel generation.

Improved catalytic performance in gas-phase dimethyl ether carbonylation over facile NH4F etched ferrierite.

Gas-phase dimethyl ether (DME) carbonylation to methyl acetate (MA) initiates a promising route for producing ethanol from syngas. Ferrierite (FER, ZSM-35) has received considerable attention as it displays excellent stability in the carbonylation reaction and its modification strategy is to improve its catalytic activity on the premise of maintaining its stability as much as possible. However, conventional post-treatment methods such as dealumination and desilication usually selectively remove framework Al or Si atoms, ultimately altering the intrinsic composition, crystallinity, and acidity of zeolites inevitably. In this study, we successfully prepared a series of hierarchical ZSM-35 materials through post-treatment with NH4F etching, which dissolved framework Al and Si at similar rates and preferentially attacked the defective sites. Interestingly, the produced pore systems effectively penetrated the [100] plane, offering elevated access to both the 8-membered ring (8-MR) and 10-membered ring (10-MR) channels. The physicochemical and acid properties of the pristine and NH4F etched ZSM-35 samples were comprehensively characterized using various techniques, including XRD, XRF, FESEM, HRTEM, Nitrogen adsorption-desorption, NH3-TPD, Py-IR, 27Al MAS NMR, and 29Si MAS NMR. Under moderate treatment conditions, the intrinsic microporous structure, acid properties, and crystallinity of zeolite were retained, leading to superior catalytic activity and stability with respect to the pristine sample. Nonetheless, severe NH4F etching disrupted the crystalline framework and created additional defective sites, bringing about faster deposition of coke precursors on the interior Brønsted acid sites (BAS) and decreased catalytic performance. This technique provides a novel and efficient method to slightly enhance the micropore and mesopore volume of industrially pertinent zeolites through a straightforward post-treatment, thus elevating the catalytic performance of these zeolites.

Preparation of core-shell ZSM-5@Beta molecular sieve and catalytic alkylation to 2,6-Dimethylnaphthalene

ZSM-5@Beta core-shell molecular sieve was prepared by dynamic hydrothermal synthesis method using ZSM-5 adhered Beta seed crystals as the core phase, and polydiallyl dimethyl ammonium chloride (PDDA) was used as a coupling agent to adhere Beta seed crystals on the surface of ZSM-5. The structure and physical properties of composite molecular sieves were characterized by XRD, N2 adsorption-desorption, SEM, TEM, ICP, NH3-TPD and Py-FTIR. The catalytic performance of composite molecular sieves for alkylation of 2-methylnaphthalene (2-MN) with methanol was investigated. The results showed that ZSM-5@Beta composite molecular sieve prepared by this method had a core-shell structure, and the particle size was about 500 nm. Compared with mechanically mixed binary molecular sieve, core-shell molecular sieve had higher specific surface area and external surface area, lower acid strength and stronger acid center density. Through the construction of core-shell interface and hierarchical porous, the catalytic activity was improved by shell phase Beta molecular sieve with 12-membered ring channel, and the catalytic selectivity was improved by core phase ZSM-5 molecular sieve with 10-membered ring channel in the alkylation reaction of 2-MN with methanol. The 2,6-/2,7-DMN ratio in the products reached 1.35, and the yield of 2,6-DMN reached 4.29%.

Comparative study on the catalytic performance of zeolite catalysts with different topologies in 1-methylnaphthalene isomerization-transalkylation coupling reaction

The isomerization-transalkylation coupling reaction between 2-methylnaphthalene and dimethylnaphthalene was studied over zeolite catalysts to produce them. The catalytic performance of zeolites with MWW, BEA, FAU and MFI topological structure was investigated and the reaction mechanism was discussed. The properties of zeolites were characterized by XRD, N2 adsorption-desorption, SEM, NH3-TPD, Py-FTIR and ICP. Compared with MFI zeolite with 10-membered ring channel, MWW, BEA and FAU zeolite with 12-membered ring channel showed better catalytic activity. BEA zeolite exhibited higher selectivity to dimethylnaphthalene, while MWW zeolites showed higher selectivity to 2-methylnaphthalene and the best catalytic stability. As a branch of MWW zeolites, HMCM-22 showed a 1-methylnaphthalene conversion of 70.27% and a 2-methylnaphthalene yield of 66.69%. It was worth noting that a relatively high yield of 2-methylnaphthalene (35.74%) and dimethylnaphthalene (19.00%) were obtained on HMCM-56 at the same time. This research has opened up a promising route using C10 aromatics as raw materials for the preparation of 2,6-dimethylnaphthalene, an important polyester monomer.

Liquid-Phase Xylene Adsorption in Unary, Binary, and Ternary Solute Systems Using Raw and Ni2+ Ion-Exchanged Clinoptilolite: Experimental Study and Thermodynamic Assessment

AbstractThe adsorptive behavior of clinoptilolite (Cpt) zeolite in its raw and nickel-exchanged form towards m-xylene/p-xylene/ethylbenzene unary, binary, and ternary mixtures was investigated. The motivation behind the research was to elucidate whether Cpt in its raw or ion-exchanged form could exhibit distinctive selective adsorption behavior. The natural Cpt (Si/Al atomic ratio = 4.59) was ion-exchanged twice with 0.5 M Ni(NO3)2 solution at 80°C for 6 h. Adsorption experiments were done at 40°C, using a 4 vol.% solution of the aromatic materials in iso-octane. The maximum amount of the total specific adsorption capacity for binary solute systems was ~0.8 and ~2.0 mmol g–1 for the raw and ion-exchanged Cpt, respectively. For the ternary solute systems, unexpectedly, this capacity increased to ~2.0 and ~3.0 mmol g–1, respectively. For binary mixtures, both forms of Cpt were selective for p-xylene. For ternary mixtures, both forms exhibited a clear selectivity for m-xylene but the Ni-exchanged Cpt was significantly higher over the concentration range studied. The unexpected increase in the adsorption capacity in ternary systems was attributed to the expulsion of tightly bound trace water molecules hindering the access of xylene molecules to the 10-member ring channels of the zeolite framework. Substitution of Mg2+ by Ni2+ in the 10-member ring channels enhanced the adsorption capacity by providing more space and stronger electrostatic interactions between the new cation and the polar m-xylene molecule.

Hierarchically porous FER zeolite obtained via FAU transformation for fatty acid isomerization

Skeletal isomerization of linear unsaturated fatty acids is important in the production of branched-chain saturated fatty acids with diverse applications. This reaction can be efficiently catalyzed by ferrierite (FER) zeolite. The reaction, however, suffers from diffusion limitations in the 10-membered ring channels. Herein, we report a method for the synthesis of hierarchically porous FER zeolite via transformation of FAU precursor driven by N-methylpyrrolidine (NMP) and amphiphile 1,2-dimethyl-3-hexadecyl-1H-imidazol-3-ium bromide (C16dMImz) as the structure-directing agent (SDA) and a mesoporogen, respectively, under hydrothermal conditions. This dual-template approach allows tuning the morphological and textural properties of the mesoporous FER materials by varying the concentration of the mesoporogen in the initial gel. The optimized FER sample is characterized by a high mesoporous volume (0.19 cm3 g-1), large external surface area (∼120 m2 g-1) and reduced crystal size in the a- and c-dimensions. This implies shortened diffusional pathways in the 10-membered ring channels. These modifications led to a significantly enhanced catalytic performance of hierarchical FER zeolite in the isomerization of fatty acids in comparison with a bulk FER reference zeolite.

Identification of Distinct Framework Aluminum Sites in Zeolite ZSM-23: A Combined Computational and Experimental 27Al NMR Study

ZSM-23 (MTT) is a silicon-rich zeolite with one-dimensional, 10-membered ring channels, which has recently attracted interest as a promising catalyst in aromatic-free methanol-to-hydrocarbons conversion. To obtain a better understanding of the catalytic activity and ultimately to design a better catalyst, it is crucial to locate the active sites in the zeolite framework. This work investigates the tetrahedral aluminum framework sites in two zeolite H-ZSM-23 samples by experimental and computational 27Al NMR spectroscopy. 27Al MQMAS NMR experiments at six different magnetic fields (4.7–22.3 T) were utilized to resolve distinct Al sites. The detected tetrahedral framework Al sites were assigned to the specific tetrahedral sites in the crystal structure by DFT calculations of the 27Al chemical shieldings. A comprehensive investigation of the structural model, basis set, and exchange–correlation potential used in the DFT calculations was performed. Two avenues were pursued for calculating the 27Al isotropic c...

Relation of Catalytic Performance to the Aluminum Siting of Acidic Zeolites in the Conversion of Methanol to Olefins, Viewed via a Comparison between ZSM-5 and ZSM-11

ZSM-5 and ZSM-11 zeolites are similar in their crystalline framework structure, acidity, morphology, and textual properties but considerably different in their catalytic performance for conversion of methanol to olefins (MTO). Such an unexpected but exciting finding was extensively explored by various techniques and density functional theory calculations. A detailed investigation shows that it is the different Al distribution in the ZSM-5 and ZSM-11 framework that causes the significant difference in MTO catalytic performance. In ZSM-5, Al atoms are enriched in the intersection, whereas in ZSM-11, the Al atoms are concentrated in the straight 10-membered ring channel. The acid sites located in the intersection enhance the arene-based cycle that generates more ethene, alkanes, and aromatics. Nevertheless, these hydrocarbon molecules can easily diffuse out of the zeolite channel, hence retarding the deposition of carbonaceous materials and increasing catalytic stability. However, the acid sites located in t...

Specific zone within 8-membered ring channel as catalytic center for carbonylation of dimethyl ether and methanol over FER zeolite

The DFT investigation of methanol and dimethyl ether (DME) carbonylation at different sites of FER zeolite is carried out in an attempt to explore whether some specific acid sites are present to selectively catalyze the desired reaction. It is shown that the surface methoxy groups (SMG), generated by the reaction of methanol or DME with the Brønsted acid sites of zeolites, preferentially forms in the 8-membered ring (8MR) and 10-membered ring (10MR) channels. Further study of the CO attack on the SMG shows that, the carbonylation reaction occurs selectively at the 6MR zone of 8MR channel of FER zeolites. This result not only provides a theoretical perspective for the experimentally observed higher carbonylation reactivity of SMG located inside the 8MR channels, but also makes the location of the reaction more accurate.

Increasing resolution of selectivity in alkene hydrogenation via diffusion length in core-shell MFI zeolite

We designed a core-shell zeolite structure comprises of palladium-deposited ZSM-5 core and silicalite-1 (S-1) shell which favors selectivity towards light olefin in hydrogenation via increased diffusion length. A well designed S-1/Pd/ZSM-5 core-shell structure was prepared via secondary crystallization of S-1 layer on the Pd/ZSM-5 core. The catalytic and selectivity performance of the S-1/Pd/ZSM-5 composite was evaluated in catalytic hydrogenation of alkenes in liquid phase. The synthesized S-1/Pd/ZSM-5 gives a much higher selectivity towards 1-hexene (87%) over cyclohexene (13%) even though both reactants are able to enter the 10-membered ring channels of the core-shell structure. The zeolitic core-shell composite also showed an increasing selectivity towards 1-hexene over 1-heptene as the S-1 layers built up, even though both are linear alkenes with similar kinetic diameter that are accessible to the MFI framework. In this work, we demonstrate a strong correlation between the thickness of the S-1 shell layer and the selectivity towards light olefins due to faster mass transfer rate. The design of the core-shell MFI structure is a new example of how selectivity in a zeolite-catalyzed reaction can be changed and enhanced without relying on typical molecular size exclusion process.

Ti-YNU-1分子筛催化氧化机理及择形选择性的理论计算

采用密度泛函理论，研究了Ti-YNU-1/H2O2体系中T3和T6位活性中心上1-己烯和环己烯环氧化反应的催化性能和反应机理。所有计算都在B3LYP/6-31G(d,p)理论水平下进行。结果表明，Ti-YNU-1分子筛中T3位的活性中心是Ti3-η2 (OOH)，T6位活性中心为Ti6-η2(OOH)-H2O 和 Ti6-η2(OOH)-CH3CN。催化活性为Ti6-η2(OOH)-H2O > Ti6-η2(OOH)-CH3CN > Ti3-η2(OOH)。在各活性中心上1-己烯环氧化反应的活化能垒高于环己烯环氧化反应，随着Ti-YNU-1分子筛中Ti含量的增加，更多的Ti插入到10元环正弦孔道中的T3位，形成更多的Ti3-η2(OOH)活性中心位点，由于孔道对环己烯的扩散限制，导致1-己烯转化率增加程度高于环己烯。 The catalytic performances and reaction mechanism of 1-hexene and cyclohexene epoxidations over active centers at the T3 and T6 sites in Ti-YNU-1/H2O2 system have been investigated by us-ing density functional theory. All calculations were performed at the theoretical level of B3LYP/6- 31G(d,p). The results indicated that the active center at T3 is Ti3-η2(OOH), and the active centers at T6 are Ti6-η2(OOH)-H2O and Ti6-η2(OOH)-CH3CN. The catalytic activity has the trend of Ti6-η2(OOH)-H2O > Ti6-η2(OOH)-CH3CN > Ti3-η2(OOH). The activation barriers of 1-hexene epoxidation over different active centers are higher than that of cyclohexene epoxidation. With the increasing of Ti content in Ti-YNU-1, more Ti species are inserted into the T3 site in the 10-membered ring channels, which accretes the numbers of Ti3-η2(OOH). Due to the distribution restrict for cyclohexene, the conversion of 1-hexene epoxidation is much higher than that of cyclohexene epoxidation.

Synthesis of ferrierite by a new combination of co-structure-directing agents: 1,6-bis(N-methylpyrrolidinium)hexane and tetramethylammonium

Ferrierite zeolite was synthesized in fluoride medium using dicationic 1,6-bis(N-methylpyrrolidinium)hexane (MPH) as a bulky structure directing agent (SDA) in combination with tetramethylammonium (TMA) as a small co-structure-directing agent (co-SDA). When trimethylamine, pyrrole or tert-butylamine were used as co-SDA, amorphous and beta zeolite (BEA framework type) were obtained, suggesting that these amines do not play a strong role as co-SDA. Only when TMA was used as co-SDA in synthesis gels with moderate pH, ferrierite is obtained; in fact, we have found a dramatic influence of the pH of the synthesis gel on the ferrierite crystallization, since even using TMA as co-SDA, ferrierite was only obtained under moderate pH values. Interestingly, ICP and CHN chemical analyses suggest that the Al content is driven by the amount of SDAs able to be hosted within the ferrierite framework, more specifically, by the nitrogen (positive charge) content available to charge-balance the negative charge associated to the incorporation of Al. A computational study showed that the most stable configuration of the ferrierite system corresponds to the occupation of the FER cages by TMA, while MPH accommodates in the 10-membered ring channels of the FER structure; the packing arrangement of MPH determines the density of positive charges, and hence the Al incorporation. Moreover, the unit cell parameters of the as-made ferrierite samples indicate that the structure is slightly expanded along the [100] direction in order to accommodate the bulky MPH dication.

Zn10(Im)20·4DBF: an unprecedented 10-nodal zeolitic topology with a 10-MR channel and 10 crystallographically independent Zn atoms.

By using a large-size amide, dibutylformamide (DBF), as a structure directing agent, a new zeolitic imidazolate framework (ZIF) was synthesized. The ZIF Zn10(Im)20·4DBF has an unprecedented zeolitic topology and features 10 crystallographically independent Zn atoms, a 10-membered ring (MR) channel and an unusual 4-connected 10-nodal net.

HP-induced supra-molecular organization of guest molecules in FER-type zeolites

The response to pressure of a synthetic all-silica ferrierite (Si-FER) and of a natural ferrierite from Monastir (Sardinia, Italy) (Mon-FER, Na0.56 K1.19 Mg2.02 Ca0.52 Sr0.14)(Al6.89Si29.04)O72 ·17.86 H2O) is here investigated combining HP synchrotron XRPD experiments and molecular dynamics simulations. The experiments were carried out by using penetrating (methanol:ethanol:water 16:3:1, m.e.w.; ethanol:water 1:3, e.w.) and non-penetrating (silicone oil, s.o.) pressure transmitting media (PTM). In Si-FER compressed in e.w., both water (w.) and ethanol molecules (e.) enter the pore system even at 0.2 GPa. The structural refinement of the data collected at 0.8 GPa reveals 8 w. and 4 e. molecules in the 10- and 6-membered ring channels, in tight agreement with the results of MD simulations. In Si-FER compressed at 0.2 GPa in m.e.w., only water molecules penetrate the 10-membered ring channels (15 per u.c.), organized in chains running along the channel axis. The interactions among the guest species and the framework oxygen atoms are very weak, due to the hydrophobicity of the framework. Upon decompression, the intruded extra-molecules are not completely released, so giving rise to new materials with different extra-framework contents. The results obtained for Si-FER compressed in m.e.w. and s.o. were compared to those obtained for Mon-FER, demonstrating that the zeolite composition and the PTM strongly influence the overall elastic parameters of the investigated samples. Specifically, Mon-FER shows a much higher rigidy than Si-FER in both media, due to the stiffening effect of the numerous extraframework species present in the natural sample. The higher rigidity of Si-FER in m.e.w. with respect to s.o. can be explained by the penetration, in the former case, of the PTM molecules, which contribute to stiffen the framework.