MFI Topology Research Articles

MFI Acid Catalysts with Different Crystal Sizes and Porosity for the Conversion of Furanic Compounds in Alcohol Media

AbstractSolid acid catalysts possessing MFI topology and different crystal sizes and porosities were explored for the conversion of carbohydrate‐biomass‐derived α‐angelica lactone and 5‐(hydroxymethyl)furfural, in 1‐butanol at T=120–170 °C, to give levulinate esters and furanic ethers. Micro/mesoporous microcrystalline catalysts were prepared by post‐synthesis base/acid treatments of ZSM‐5 zeolite; the influence of the desilication (base) conditions on the material properties was investigated. A nanocrystalline ZSM‐5 sample was synthesised by using hydrothermal, dynamic conditions and used as a reference material. A comparison of the catalytic performances of materials featuring different morphological, textural, and acid properties highlights a complex interplay between the acid and textural properties. The best‐performing catalyst (MZS0.6) was obtained by post‐synthesis‐treatment; fairly good catalytic stability was confirmed by catalyst recycling, contact tests, and characterisation of the spent catalyst. MZS0.6 was compared with the macrorecticular ion‐exchange resin Amberlyst‐15, chosen as a benchmark solid acid catalyst, in the two reaction systems.

Gas phase glycerol oxidative dehydration over bifunctional V/H-zeolite catalysts with different zeolite topologies

The oxidative dehydration of glycerol to acrylic acid can be performed in one single step using bifunctional catalysts containing both acid and redox sites. In this sense, zeolites containing transition metals are promising catalysts. Zeolites of different topologies: FAU, FER, MEL, MFI, MOR, MWW and OFF were synthesized and further impregnated with 5% vanadium. The catalysts were characterized and evaluated in the gas phase glycerol oxidative dehydration. All catalysts showed high conversions of glycerol (100-78%). The acrolein selectivity decreases with the total density of acid sites in these zeolites. The selectivity to acrylic acid is related to the ability of each topology of stabilizing the redox pair V5+/V4+. The best performances were observed for zeolite catalysts with MWW, BEA and MFI topologies.

14 N NMR of tetrapropylammonium based crystals

We have investigated using 14N NMR different types of materials containing tetrapropylammonium cations. We consider the tetrapropylammonium bromide crystal as well as two different microporous materials silicalite-1 and AlPO-5, with MFI and AFI topology respectively, where the tetrapropylammonium cation plays the role of structure directing agent. 14N NMR quadrupolar coupling parameters were determined experimentally for all the crystals. In addition calculations based on Density Functional Theory with empirical dispersion (DFT-D) were performed on the MFI type zeolite. The sensitivity of the 14N quadrupolar coupling parameters to the spatial distribution of the anions in the zeolite’s framework is emphasized.

Ammonia-Containing Species Formed in Cu-Chabazite As Per In Situ EPR, Solid-State NMR, and DFT Calculations.

Nowadays, the most attractive technology for the elimination of nitric oxides from the exhaust gas of diesel vehicles is the selective catalytic reduction with ammonia (NH3-SCR-NOx) using Cu zeolite with the chabazite structure as the catalyst. Isolated copper species are the active sites, but the reaction intermediates and the overall reaction mechanism are still under debate. Here, we study the interaction of ammonia with zeolite Cu-SSZ-13 (CHA topology) with a uniform distribution of Cu(2+) sites prepared in one pot and a conventional Cu-ZSM-5 (MFI topology) for comparison. In situ EPR and solid-state NMR spectroscopies combined with DFT calculations have allowed the identification of NH4(+), [Cu(NH3)5](2+), [Cu(Of)2(NH3)2](2+), [Cu(Of)3NH3](2+), [Cu(NH3)2](+), and [CuOf(NH3)](+) (Of being framework oxygen) under different conditions. The results demonstrate that ammonia is able to reduce Cu(2+) to Cu(+) and provide new information on the species formed in Cu-SSZ-13, which have important implications for the elucidation of the SCR reaction mechanism.

Hydrogen production through catalytic methane decomposition promoted by pure silica materials

This work reports for the first time that DeCH4 reaction can be carried out over pure silica porous solids working under reaction conditions similar to those employed with carbon catalysts. Thereby, a variety of pure silica samples, with different structural and textural properties have been investigated: amorphous silica (am-SiO2), two zeolitic materials with MFI topology (conventional and hierarchical silicalite-1) and two ordered mesoporous silicas (MCM-41 and SBA-15). In all cases, the carbon generation is not observed from the beginning of the methane supply, but the presence of an induction time is noticed. This effect has been assigned to the fact that the real active sites are not present in the raw silica, being formed during the induction time by reaction between methane molecules and defective silica sites to form –Si–C– species. Among the different silica materials, great variations in the DeCH4 catalytic activity are observed. The SBA-15 sample exhibits the highest activity and an exceptional stability against deactivation by carbon deposition. The major benefit derived from the use of silica materials versus ordered mesoporous carbons in DeCH4 is their easier and more economical manufacture at large scale.

Quantification of Silver Sites in Zeolites: Carbon Monoxide Sorption Monitored by IR Spectroscopy

This work was aimed to provide a well-established approach for the quantification of silver sites in zeolites. The experimental procedure based on carbon monoxide sorption in silver exchanged zeolites ZSM-5, Y, and X was monitored by IR spectroscopy. With regard to the Lambert–Beer law the values of the absorption coefficients of the IR bands of CO interacting with exchangeable cations (Ag+) and metallic species (Ag0) were attained. Subsequently, the concentrations of silver species of different kinds were calculated. The values of the absorption coefficients are valid for zeolites of FAU and MFI topologies; thus, they are argued to be used for zeolites of other structures.

Adsorbing/Absorbing Effect of Nanosized Metal Oxide and Zeolite Nanocrystals in Lithium Sulphur Batteries

Due to their low cost and high energy density, rechargeable Li-S batteries are among the most promising energy storage devices. Sulphur has a theoretical gravimetric energy density up to five times higher than that of present lithium-ion battery technologies. Despite significant recent advances, there are still some challenges. Upon sulphur reduction and oxidation, intermediate soluble lithium polysulphides readily diffuse into the electrolyte, causing capacity fading and poor columbic efficiency in the cell. To overcome this problem, strong adsorption and absorption materials have been employed to adsorb/absorb lithium polysulphides. As an additive in the sulphur cathode it has been demonstrated that various nano-sized oxides (such as Mg0,6Ni0,4O, Al2O3, La2O3) and mesoporous silicates (SBA-15) can effectively trap polysulphides [1-4].In this contribution we report use of Silicalite-1 zeolite as an additive in the cathode composite in the Li-S batteries. Silicate-1 is a microporous, silica-based molecular sieve with a MFI topology of the tetrahedral framework. Incorporation of transition metals into their framework generates different types of catalytically active sites. MnS-1 (manganese silicalite-1) nanosized crystals (arround 200 nm) have been synthesized under classical hydrothermal procedure and showed Mn3+ incorporated into the silicalite-1 framework as framework manganese. By contrast, MnS-1 synthesised under microwave hydrothermal procedure resulted in incorporation of Mn3+ into the silicalite-1 framework as extra-framework manganese in forms of manganese oxide nano-particles [5-6].Galvanostatic cycling showed good capacity retention of the Li-S cells through the use of zeolite additives as polysulphide reservoirs. We examined the role of silica surface, pore absorption and manganese oxide adsorption. MnS-1 crystals with a small amount of nano-sized manganese oxide particles in the structure appear effective at retaining the soluble polysulphides at the cathode and are limiting the fraction that takes part in the sulphur shuttle mechanism. We assume that, most likely, additionally to the zeolites, the nano-sized manganese oxide serves as an adsorbent of the polysulphides in the cathode material. By utilizing 9 wt.% MnS-1 in cathode material we achieved a higher specific capacity and cycle efficiency in comparison with cathode material without zeolite additive and with 9 wt.% of mesoporous SBA-15 additive. The possible mechanism(s) will be discussed based on results obtained by in operando analytical techniques developed in our lab [7,8]. Acknowledgement: This research has received founding from the Slovenian Research Agency and the European Union Seventh Framework Programme under grant agreement No. 314515 (EUROLIS).

Synthesis of Hierarchical Sn-MFI as Lewis Acid Catalysts for Isomerization of Cellulosic Sugars

Hierarchical stannosilicate molecular sieves with ordered mesoporosity and MFI topology (three dimensionally ordered mesoporous imprinted (3DOm-i) Sn-MFI) were successfully synthesized within the confined space of three dimensionally ordered mesoporous (3DOm) carbon by a seeded growth method. The obtained 3DOm-i Sn-MFI consisting of 30 nm spherical elements forming an opaline structure contains highly ordered mesopores ranging from 4 to 11 nm. Compared with conventional Sn-MFI, 3DOm-i Sn-MFI exhibits superior catalytic performance for the isomerization of cellulosic sugars. No diffusion limitation was observed for the isomerization of a triose sugar, dihydroxyacetone (DHA), into methyl lactate (ML). The presence of weak Bronsted acid in the 3DOm-i Sn-MFI catalyst facilitates the reaction by catalyzing the formation of an intermediate, pyruvaldehyde (PA). 3DOm-i Sn-MFI offers significant improvements for the isomerizations of C5 and C6 sugars, such as xylose and glucose, by greatly enhancing molecular tran...

Confinement of Water in Hydrophobic Nanopores: Effect of the Geometry on the Energy of Intrusion

Water confinement in the hydrophobic nanopores of highly siliceous zeolite having MFI and CHA topology is investigated by high pressure manometry coupled to differential calorimetry. Surprisingly, the intrusion of water is endothermic for MFI but exothermic for CHA. This phase transition depends on the geometry of the environment in which water is confined: channels (MFI) or cavities (CHA). The energy of intrusion is mainly governed by the change in the coordination of water molecules when they are forced to enter the nanopores and to adopt a weaker, hydrogen-bonded structure. At such a nanoscale, the properties of the molecules are governed strongly by geometrical restraints. This implies that the use of classical macroscopic equations such as Laplace-Washburn will have limitations at the molecular level.

Hexane cracking catalyzed by MSE-type zeolite as a solid acid catalyst

MCM-68 (MSE topology) with three-dimensional 12–10–10-ring channel system was focused on, expecting the hybrid character of ZSM-5 (MFI topology) and beta (*BEA topology), as a solid acid catalyst for hexane cracking reaction. The proton form of MCM-68 without dealumination having Si/Al ratio around 12 was deactivated rapidly during the reaction due to heavy coke formation, whereas dealuminated MCM-68 exhibited sufficient catalytic activity and durability to coke formation for hexane cracking at the reaction temperatures from 450 to 600°C. The dealuminated MCM-68 also had higher propylene selectivity of 45–50% in comparison with other zeolite catalysts such as ZSM-5, mordenite and beta at the reaction temperatures of 450 to 600°C. Both the MCM-68 catalysts before and after dealumination were regenerated after the reaction at 600°C to exhibit almost the same performance as the initial catalyst. At higher reaction temperature such as 650°C, the catalyst was deactivated rapidly mainly due to coke formation again. In order to avoid this deactivation, modification of MCM-68 with lanthanum oxide simply by impregnation was performed. The La-modification mainly deactivated the active site on the external surface and was found to be an effective way for avoiding heavy coke formation to maintain catalytic activity and selectivity to propylene.

Synthesis, characterization, and catalytic performance of bifunctional titanium silicalite-1

A series of bifunctional Ti-molecular sieves (M-TS-1, M = Al, B, or Fe) containing different trivalent ions (Al3+, B3+, or Fe3+), with MFI topology, were synthesized using tetrapropylammonium bromide, silica sol, and n-butylamine as a template, base, and Si source, respectively. The simultaneous presence of Ti and trivalent ions in lattice positions provided catalysts with activity in both oxidation and acid-catalyzed reactions. The samples were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, ultraviolet-visible spectroscopy, NH3 temperature-programmed desorption, inductively coupled plasma atomic emission spectroscopy, and N2 adsorption-desorption isotherms. The results showed that the numbers and strength of acid sites of TS-1 were enhanced by the incorporation of trivalent ions. Using selective oxidation of ethylene as the probe reaction, the catalytic properties of M-TS-1 were investigated. The results showed that Al-TS-1 and B-TS-1 had better catalytic properties; conversion and utilization of H2O2 reached 95% and 90%, respectively, and the yield of ethylene glycol plus its monomethyl ether was greater than 10%.

Synthesis and Catalytic Activity of Sn-MFI Nanosheets for the Baeyer–Villiger Oxidation of Cyclic Ketones

Stannosilicate zeolites with nanosheet morphology and MFI topology (Sn-MFI-ns) are successfully synthesized with an amphiphilic organic structure-directing agent. Sn source, Si/Sn ratio, crystallization time and temperature impact framework Sn incorporation and nanosheet morphology. Optimal synthesis conditions generate Sn-MFI-ns with high crystallinity and isolated framework Sn sites. Nanosheets are ∼2 nm thick in the (010) direction, resulting in large intersheet mesopore volumes and external surface areas exceeding 430 m2/g. Unlike bulk Sn-MFI, Sn-MFI-ns is highly active in the Baeyer–Villiger oxidation of bulky cyclic ketones using hydrogen peroxide (H2O2). Although Sn-MFI-ns and Sn-MCM-41 have comparable activity and oxidant efficiency, the nanosheets exhibit drastically higher thermal and hydrothermal stability.

Flexibility windows and compression of monoclinic and orthorhombic silicalites

Silicalite, a high-silica zeolite with MFI topology, undergoes pressure-induced amorphisation (PIA) when compressed with nonpenetrating pressure media. PIA is prevented by penetrating pressure media. In several zeolites, links have recently been found between pressure-induced phase transitions and the flexibility window, a geometric property of the framework identified by geometric simulation. We have analyzed structural data from compression experiments on silicalite, and we find that PIA occurs while the structure lies within its flexibility window. Penetrating media, which prevent PIA, push the structure outside the flexibility window. Thus framework flexibility is required for PIA to occur in silicalite. This link between amorphisation and flexibility is further evidence of the deep connections between framework geometry, flexibility, and the physical properties of zeolites.

Low temperature conversion of linear C 4 olefins with acid ZSM-5 zeolites of homogeneous composition

Conversion of linear butenes over ZSM-5 zeolites leads to a large variety of products, from olefins to aromatics. At low temperature, these products are mainly olefins from C 3 = to C 13 =, with a predominance of dimeric products. The analysis of the product stream obtained by the reaction of n-butenes over several materials with MFI topology, but with different aluminum content provides evidence for an oligomerization–cracking–realkylation mechanism. The reactions occur predominantly in the catalyst bulk or at the external surface, depending on the amount of coke developed inside the catalyst. This behavior is determined by the concentration of framework Al and associated silanol groups, inducing coking. For Al-rich MFI samples, the amount of hard coke is sufficient to block the access of reactants to internal acid sites. As a result, extra-crystalline catalysis dominates, while the appearance of the individual products is consistent with that predicted by classical carbocation theory. For siliceous samples, hard coke formation is less pronounced, and evidence for shape selective product formation is present. Expected relations among structural, morphological and acidic properties of all MFI materials have been confirmed by XRD, SEM and BET and by 27Al MAS NMR, NH 3-TPD and FTIR.

Synthesis and application of colloidal nanocrystals of the MFI-type zeolites

The colloidal dispersion containing the nanosized zeolites with the MFI topology has been successfully prepared. A pre-aging process of the mother gel at 80 °C for 24 h before the crystallization was important for the formation of the nanosized zeolites. We have also found that silicalite-1 nanocrystals av. 62 nm in size were formed by the addition of acidic amino acids into the mother gel. The particle size of the zeolites can be controlled ranging from 62 to 530 nm by changing the amount of water, aging process, crystallization time and temperature and the addition of organic molecules. Furthermore, nanosized titanium silicalite-1 (TS-1) with the size of 50–130 nm has been successfully synthesized by the addition of a Ti source into the synthesis gel of the silicalite-1 nanocrystals. The nanosized TS-1 exhibits a higher catalytic activity in the epoxidation of cyclohexene than the microsized ones. Finally, we demonstrate the preparation of thin films of the silicalite-1 and TS-1 nanocrystals onto a silicon substrate by a dip-coating technique.

ChemInform Abstract: UTM-1: An Eight-Membered Ring Zeolite with the Basic Building Chains of the MFI Topology.

The structure of zeolite UTM-1 has been determined from synchrotron X-ray powder diffraction pattern by direct methods and Rietveld refinement. The framework of UTM-1 consists of pocket-like cages connected by sharing eight-membered rings forming one-dimensional channels. The structure can be completely described by the assembly of chains of 58 cages. Identical chains are found in MFI topology; the zeolites UTM-1 and ZSM-5 are distinguished from each another by the way the chains are assembled.

Synthesis and characterization of NTS material and its oxidation desulfurization properties

The development of desulfurization technology involving the onsite direct generation of hydrogen peroxide (H 2O 2) from H 2 + O 2, followed by H 2O 2 oxidation to organic oxides without conventional refining is regarded as one promising approach for reducing capital and operating costs. The objective of our research is to provide bi-functional catalytic materials based on a combined process for the oxidative desulfurization (ODS) using H 2O 2 in situ generated. We have prepared a series of new bi-functional titanosilicate (NTS, titanium silicalite combined with noble-metal loading), which have been synthesized by combining noble-metal sources with modified titanium silicalite under basic conditions. Here, the synthesis and characterization of NTS samples, and their ODS properties are presented. The samples were characterized by various analytical techniques, and their direct ODS performances were investigated. The results indicate that NTS shows well ordered MFI topology and with hollow structure; NTS combined with noble-metal shows potential for application in direct ODS with H 2 + O 2 in one-step process.

NHTS: A Hollow, Noble‐Metal‐Modified Titanium Silicalite

AbstractThe major drawback of direct oxidation technology (onsite hydrogen peroxide production followed by its conversion into organic oxides without refining) is the design and preparation of the bifunctional catalysts used therein. Herein we present a bifunctional catalytic material (NHTS), which is synthesized by a revised semi‐in‐situ method that allows a noble metal to be distributed throughout the titanosilicate framework and also results in a redistribution of active Ti species throughout the crystals, thereby enriching the surface of the hollow crystals with catalytic species. This compound has been characterized by various techniques and its activity and selectivity for the direct epoxidation of propylene investigated. The results indicate that NHTS shows a very ordered MFI topology, with the noble metal incorporated in the framework, and a hollow structure, which makes it a good alternative for catalytic oxidations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Hydrothermal Synthesis of Titanium Silicalite-1 Structurally Directed by Hexamethyleneimine

Titanium silicalite-1 (TS-1) with the MFI topology has been synthesized successfully in the absence of alkali metal ions with the cooperative effects of active seeds and the structure-directing agent hexamethyleneimine (HMI). The physicochemical properties and structures of the products were characterized by various techniques. The coexistence of HMI and primary and/or secondary building units of the MFI structure in the synthesitic gels was essential for the nucleation and crystallization of TS-1. The nature and preparation conditions of the seed precursors had a great influence on the crystallization process and the incorporation of titanium atoms into the framework. It was found that a synergistic effect between HMI and the precursor seeds led to the full crystallization of TS-1. Other synthesis parameters such as boron addition, silicon source, and crystallization time were also investigated. Moreover, the present synthesis system is also applicable to the preparation of other MFI analogues.

Arsenic adsorption from aqueous solution on synthetic zeolites

The adsorption of arsenic from aqueous solution on synthetic zeolites H-MFI-24 (H24) and H-MFI-90 (H90) with MFI topology has been investigated at room temperature (r.t) applying batch equilibrium techniques. The influences of different sorption parameters such as contact time, solution pH, initial arsenic concentration and temperature were also studied thoroughly in order to optimize the reaction conditions. The adsorption of arsenic on to H24 and H90 follows the first-order kinetics and equilibrium time was about 100 min for both the adsorbents. The first-order rate constant ( k), 4.7 × 10 −3 min −1 for H90 is more than two times higher in magnitude compared to 2.1 × 10 −3 min −1 for H24. Adsorption performance of H90 is higher compared to H24 due to it's highly mesoporous nature which in turn accelerates the diffusion process during adsorption. As(V) sorption capacity derived from Langmuir isotherm for H24 and H90 are 0.0358 and 0.0348 g g −1, respectively. Arsenic uptake was also quantitatively evaluated using the Freundlich and Dubinin–Kaganer–Radushkevich (DKR) isotherm models. Ion exchange between adsorbent's terminal aluminol groups with different predominant forms of arsenate in solution is one of the various important reactions occurred during adsorption process.