Lamellar MFI Research Articles

Ex-situ catalytic fast pyrolysis of wood chips over lamellar MFI zeolite supported nickel catalyst

Lamellar MFI zeolite and lamellar MFI zeolite supported nickel were synthesized and examined for ex-situ catalytic upgrading of the vapors (without using any fluidized gases such as N2 and H2) resulted from fast pyrolysis of wood chips in comparison to its commercial MFI zeolite and its supported nickel counterparts. Pyrolysis tests were carried out using a catalytic augur reactor at atmospheric pressure, while pyrolysis unit was operating at 450 °C and upgrading unit at 420 °C, respectively. The introduction of nickel with a high dispersion over the zeolitic supports caused a significant increase in the products of aromatic compounds. Moreover, the addition of nickel to zeolite supports changed their acidity and decreased the total number of acid sites and the ratio of Brønsted to Lewis acid sites as determined by pyridine-FTIR spectroscopy. The use of lamellar zeolite catalysts increased the efficiency of catalytic cracking of pyrolysis vapors and their modification with nickel helped tuning the Lewis acidity to further increase catalytic cracking which resulted in a higher yield of the low molecular weight aromatics present in the bio-oil.

Assessment of coke deposits on lamellar metal-modified MFI zeolites in ethylene transformation to aromatic liquids

The effects of meso-/microporous structure and metal-additive (Ga or Zn) of lamellar MFI catalysts on the characteristics of coke deposits during ethylene-to-aromatic liquids conversion were investigated. The nature, composition, and location of coke deposits in spent lamellar catalysts were analyzed and compared to those on the microporous MFI counterparts, using FTIR, UV–Vis, GC–MS, and argon adsorption-desorption. The total amount of coke and the changes in coke nature during catalyst regeneration were studied by MS/FTIR combined with temperature programmed oxidation. The lamellar meso-/microporous structure of MFI reduces the coke quantity and the heavy coke fractions. The coke preferentially deposites on external surface of lamellar zeolite due to the lower diffusion limitation for bulky coke precursors. Metal-additive changes the catalyst acidity and decreases the coke formation rate, especially when zinc is used. Therefore, the coke formation on zeolite can be tuned by modulating the textural and acidity properties of the metal-modified catalyst.

Influences of metal-modification and lamellar zeolite structure on ethylene to liquid aromatics conversion reaction using MFI catalysts

The effects of meso-/microporous structure and metal-modification with gallium or zinc on catalytic performances of lamellar MFI zeolites in ethylene conversion reaction to liquid aromatics were investigated. TEM, XRD, Ar adsorption-desorption, UV-Visible spectroscopy, and H2-TPR measurements showed that the zeolite structure is a pivotal factor for controlling the type of metal dopant species forming on zeolite, their size, and their distribution. Adding metal dopants to zeolite structure decreased the Brønsted to Lewis (B/L) acid site ratio in the zeolites and improved their catalytic performance. As a result, metal-modified lamellar MFI zeolites showed higher liquid aromatics yield and selectivity for mono-benzene alkylated aromatics and lower coke formation rate compared to their microporous commercial MFI analogies. Zinc-loaded lamellar MFI had the most efficient catalytic performance among all studied catalysts. This phenomenon can be explained by higher accessibility of reactants to active sites and facilitated transport of products from lamellar structure of this zeolite and the low B/L acid site ratio of this catalyst provided by metal-modification, which is more suitable for ethylene aromatization. A bifunctional reaction mechanism has been proposed based on the analysis results of reaction product distributions that demonstrates the effect of both zeolite acid sites and metal sites in conversion of ethylene to liquid aromatics over MFI zeolite catalysts.

Mesopore differences between pillared lamellar MFI and MWW zeolites probed by atomic layer deposition of titania and consequences on photocatalysis

Abstract The pillared MWW (PMWW or MCM-36) and pillared MFI (PMFI) are two prominent representatives of meso-/microporous lamellar zeolites, which are made by pillaring of layered MCM-22(P) and multilamellar MFI precursors, respectively. They both consist of a 10-membered ring sinusoidal micropore channel within each zeolitic layer and mesopore voids created by pillars between two adjacent zeolitic layers. Although catalytic activities of PMWW and PMFI have been compared, identification of mesopore differences between these two pillared lamellar zeolites has not been attempted. In this work, we report the differences in mesopore characteristics between PMWW and PMFI zeolites probed by atomic layer deposition (ALD) of titania (ALD-TiO2) species and a combination of structural, textural, composition and catalytic property analyses of the samples before and after ALD treatment, respectively. The results suggest PMFI has cylindrical mesopores with uniform sizes from pore entrance to main body, while PMWW has ink-bottle mesopores with the neck size much smaller than pore body. The communication between micropore and mesopore in PMFI is direct, but no communication exists in PMWW zeolites. The ALD-TiO2 process considerably modified external surface composition of PMFI and PMWW zeolites, which consequently led to a new application of the pillared lamellar zeolite materials, i.e., photo-catalytically active meso-/microporous zeolites for environmental remedy reactions.

Synthesis of hierarchical lamellar MFI zeolites with sequential intergrowth influenced by synthetic gel composition

Abstract Hierarchical lamellar zeolites, comprised of both micro- and mesoporosity, afford high active site accessibility and mass transport in processing of bulky molecules. Here, we report the synthesis of hierarchical lamellar MFI zeolites with sequential intergrowth that is induced by composition variation in the standard recipe of 100SiO2/0.5Al2O3/3C22-6-6/18.5Na2O/4000H2O, where C22-6-6 stands for the diquaternary ammonium surfactant ([C22H45 N+(CH3)2 C6H12 N+(CH3)2 C6H13]Br−2) template. The influences of C22-6-6 concentration, alkalinity, and aluminum amount on the intergrowth of hierarchical lamellar MFI zeolites were investigated. The consequences of intergrowth on mesoporosity were analyzed. In all studied synthesis conditions except for very low alkalinity, hierarchical lamellar MFI zeolites were successfully crystallized. The increasing template concentration in the synthesis gel resulted in an increase in intergrowth and thus mesoporsotiy in the hierarchical MFI products. The increasing alkalinity led to an increase and then a decrease in mesoporosity in the hierarchical MFI products, which reflects the same trend in intergrowth in the hydrothermal synthesis process. The aluminum concentration, however, did not significantly affect the intergrowth and mesoporosity of the resultant hierarchical MFI zeolites. The sequential intergrowth achieved by simple variation in the synthesis composition for lamellar MFI zeolites resulted in higher structure hierarchy, mesoporosity, and acid site accessibility in one-step.

Synthesis of Hierarchically Porous Zeolite Composites with Enhanced Catalytic Activity: Effect of Different Long-Chain Structure Directing Agents

A two-section temperature strategy was employed to achieve micromesoporous composites with five kinds of long-chain alkyl quaternary ammonium salts as single template. Zeolites with an ordered two-dimensional hexagonal mesopore and crystallized MFI domain were successfully obtained. Gemini quaternary ammonium salt surfactants C18N2 and C22N2 are effective in directing the structure of MCM-41 than CTAB at 100 °C and will transform to lamellar MFI structures at 150 °C gradually. While single quaternary ammonium salts C18N and C22N direct lamellar M41s at 100 °C and transform to mesoporous structure at a higher temperature of 150 °C, it is possible to get a composite of microporous and mesoporous material with a surface area as high as 1046 m2 g–1. Catalytic performance of typical hierarchical zeolites was evaluated by Claisen-Schmidt condensation of bulky reactants. The excellent conversion suggested the synergy effects of improved large molecule diffusion in mesopores and highly separated MFI domains as ca...

Three-step cascade over a single catalyst: synthesis of 5-(ethoxymethyl)furfural from glucose over a hierarchical lamellar multi-functional zeolite catalyst

Glucose conversion over hierarchical lamellar MFI–Sn/Al: accommodating a three-step reaction cascade over a single catalyst for a high yield of 5-(ethoxymethyl) furfural.

Computer simulations of the structure and properties of organic pillared MFI zeolite catalyst

Multifunctional porous hybrid materials have recently received a lot of attentions because they combine the advantages of incorporating both inorganic oxides and organic species into the structure to solve the limitation of sole component material. This paper reports a type of model of organic pillared MFI zeolite catalyst, in which the full-atom mimetic model is constructed by using molecular modeling technique. Dreiding force field is used to calculate the interactions between sorbate–sorbate and sorbate–sorbent in the organic pillared MFI zeolite. The optimized model is characterized by calculating low-angle and high-angle X-ray diffraction patterns. Besides, the adsorption behavior of benzene and toluene is also investigated through the mimetic model. Simulated adsorption isotherms of benzene and toluene are agreement with the experimental data at low pressure. Density distributions of benzene and toluene show that toluene adsorbs preferentially in the region of interlayer space of lamellar MFI zeolite while benzene tends to adsorb in the area of micropores at low pressure. With increasing pressure, the guest molecules gradually fill in the area of micropores and mesopores of the organic pillared MFI zeolite. Moreover, the developed strategy in the present work can be applied to build other model for organic pillared zeolite catalyst by arranging different zeolite frameworks or organic species.

BEA nanosponge/ultra-thin lamellar MFI prepared in one-step: Integration of 3D and 2D zeolites into a composite for efficient alkylation reactions

The synthesis of hierarchical meso-/microporous zeolite materials with spatially controlled morphology, meso-/microporosity, and acidity is an expanding area of research interest for a wide range of applications. Here, we report a one-step dual template synthesis method for integration of 3-dimensional (3D) BEA nanosponge and ultra-thin 2D lamellar MFI into a new type of hierarchical meso-/microporous zeolite composite structures. Specifically, the 2D layered MFI nanosheets were laid over the surface of or interdigitated into the 3D BEA particles in the bulk BEA nanosponge-lamellar MFI (BBLM) zeolite structure, which generated a unique morphology of interconnected micropores and mesopores underneath the ‘skinning’ shell (∼3–10nm) of MFI nanosheets. The BBLM zeolites have higher mesoporosity than either bare BEA or lamellar MFI zeolites. The micropore size decreases with increasing lamellar MFI component in the composite. The fraction of external acid sites of BBLM zeolite composite, represented by the percentage of active sites accessible to bulky organic base molecules, decreases with increasing MFI component. Additionally, the types of acid sites are diversified in the BBLM composites compared to either bare BEA or lamellar MFI zeolites. The catalysis tests using conversion of benzyl alcohol in mesitylene showed that BBLM zeolites had significant higher activity and durability than single zeolites or their physical mixture. The BBLM zeolite composite provides a good model catalyst with integrated 2D-3D structures and meso-/microporosity for studying a series of important catalytic reactions in hierarchical zeolites. The one-step dual template synthesis method described herein is versatile and facile, which may prove to be a general platform for hierarchical zeolite composite design at the unit-cell scales of zeolites and with potentially broader applicability to other porous materials.

A density functional theory study of the structure of pure-silica and aluminium-substituted MFI nanosheets

The layered MFI zeolite allows a straightforward hierarchization of the pore system which accelerates mass transfer and increases its lifetime as a catalyst. Here, we present a theoretical study of the structural features of the pure-silica and aluminium-substituted MFI nanosheets. We have analysed the effects of aluminium substitution on the vibrational properties of silanols as well as the features of protons as counter-ions. The formation of the two-dimensional system did not lead to appreciable distortions within the framework. Moreover, the effects on the structure due to the aluminium dopants were the same in both the bulk and the slab. The principal differences were related to the silanol groups that form hydrogen-bonds with neighbouring aluminium-substituted silanols, whereas intra-framework hydrogen-bonds increase the stability of aluminium-substituted silanols toward dehydration. Thus, we have complemented previous experimental and theoretical studies, showing the lamellar MFI zeolite to be a very stable material of high crystallinity regardless of its very thin structure.

Spatial distribution and catalytic performance of metal–acid sites in Mo/MFI catalysts with tunable meso-/microporous lamellar zeolite structures

The lamellar MFI zeolite with tunable meso-/microporosity was prepared by a dual template synthesis method. Implications of the tunable meso-/microporosity on the spatial distribution and catalytic performance of metal–acid sites in Mo/lamellar MFI catalysts were studied. The number of free Brønsted acid sites increases linearly, accompanied by a linear decrease in Mo dispersion, with decreasing external surface areas in catalysts. The Mo–acid active sites coexisted on the external surface or mesopores of the catalysts linearly depends on the hierarchy factor, being the product of relative micropore volume and relative external surface area. The reaction rate and product selectivity of Mo/lamellar MFI in direct methane aromatization reactions are consistent with the trends of changes in zeolite porosities. These results imply that a balance between the meso- and microporosity in zeolite and the resultant active site distribution can be realized for desirable catalysis by simple one-step dual template synthesis of zeolites.

Efficient cycloaddition of epoxides and carbon dioxide over novel organic-inorganic hybrid zeolite catalysts.

Organic-inorganic hybrid zeolites with the MFI-type lamellar structure serve as efficient solid Lewis base catalysts for solvent-free synthesis of a variety of cyclic carbonates from corresponding epoxides and carbon dioxide. The ion-exchange with iodide, in particular, renders these materials an excellent catalytic activity and good recyclability.

Textural and catalytic properties of Mo loaded hierarchical meso-/microporous lamellar MFI and MWW zeolites for direct methane conversion

The consequences of meso-/microporous zeolite structures on distribution and activity of active sites (Brønsted acid and metal sites) in molybdenum (Mo) impregnated lamellar MFI and lamellar MWW zeolites were investigated in direct methane aromatization (DMA) reactions. In comparison with their microporous analogies (Mo/MFI and Mo/MWW), the mesopores in the Mo/lamellar MFI and Mo/lamellar MWW zeolites facilitated the dispersion of Mo in zeolite micro-channels. The catalytic DMA reactions showed that the Mo loaded lamellar MFI and lamellar MWW zeolites enabled efficient methane conversion, aromatic product formation, and coke accumulation in the initial stage of reaction, while their performances were similar to those of Mo/MFI and Mo/MWW catalysts in the long term run. A plausible explanation to this scenario is that active sites in Mo/lamellar MFI and Mo/lamellar MWW can be accessed by reactants through both micropores and mesopores. The facilitated transport and accessibility to active sites by mesopores accounted for initial fast reaction and deactivation rates of Mo loaded lamellar zeolites. After mesopores were clogged by deposited coke in DMA reactions, micropores of zeolites were responsible for the long term catalyst performances, which were similar to Mo loaded microporous zeolites.

The effect of MFI zeolite lamellar and related mesostructures on toluene disproportionation and alkylation

The effect of MFI zeolite nanosheet morphology and related mesostructures on the accessibility of acid sites evaluated from FTIR spectra of different adsorbed probe molecules and conversions and selectivities in toluene disproportionation and alkylation with isopropyl alcohol was investigated. Two-dimensional MFI lamellar zeolite (1.5 nm thickness of layers) and related mesoporous sponge morphologies, most probably with 10-ring channel system not yet structurally fully determined, were synthesized and characterized by XRD, SEM, TEM, and adsorption measurements. FTIR spectroscopy using pyridine, deuterated acetonitrile and 2,6-di-tert-butyl pyridine evidenced high concentrations of accessible Lewis acid sites at the expense of Bronsted acid sites. Ordered mesoporous zeolites exhibited slightly higher toluene conversion in its alkylation with isopropyl alcohol than lamellar MFI or conventional MFI due to easy access to active sites. The lamellar zeolite consisting of less than a unit cell layer was slightly more active than MFI but still exhibited high selectivity to p-cymene. It evidences that alkylation of toluene with isopropyl alcohol proceeds mainly in the 10-ring channel system of MFI zeolite, although the effect of large external surface cannot be neglected. Increased para-selectivity compared with thermodynamic value is achieved even in the case of extremely thin zeolite nanosheets.

Mesoporous silica nanoparticles from a clear sol and their transformation to lamellar silicalite-1 particles and films

Mesoporous silica nanoparticles were formed from hydrothermal treatment of a clear synthesis sol. They were transformed to lamellar silicalite-1 by continued hydrothermal synthesis, during which intermediate mesostructures appeared at different stages of the transformation. Steam-assisted crystallization (SAC) was performed on coatings of these intermediate mesostructures. The SAC approach gave an intergrown lamellar silicalite-1 coating containing single-unit-cell-thick (2.0 nm) nanosheets. The steam-assisted crystallization method introduced here can be used to form membranes and catalytic coatings of lamellar MFI.