Mesoporous MFI Research Articles

Unveiling the generation of mesoporous MFI zeolites with one-dimensional fins in the assistance from small quaternary ammonium cation and its application in propane aromatization

In this work, a kind of ZSM-5 zeolite with one-dimensional fins growing along the [010] direction has been successfully synthesized utilizing both tetrapropylammonium hydroxide (TPAOH) and tetramethylammonium hydroxide (TMAOH) as co-templates. With the aid of molecular dynamic simulations and a series of experimental evidences, the formation mechanism of the one-dimensional feature is determined to arise from the synergic effects between TPA+ and TMA+. Two TPA+ and three TMA+ would co-exist in a unit MFI cell at a certain crystallization period depending on the composition of zeolite and precursor, and this configuration ensures a minimum stabilization energy required for the growth along [010] direction. Investigations manifest these needle-like fins with diameters of ca. 60 nm could function as pseudo nano crystals and introduce additional pores ranging from 10 to 90 nm, which effectively promotes the diffusion capability and substantially improves the catalytic performance in propane aromatization.

Pore Engineering of MFI Zeolite Membranes

A mesoporous MFI zeolite membrane was synthesized using polyacrylamide as a secondary template to separate nickel, chromium, and nitrate ions from water. Various analytical methods were employed to characterize the zeolite powders and membranes. Subsequently, tests were conducted to evaluate water permeation and the rejection of heavy metals and nitrate ions. The incorporation of 0.03 kg kg–1 polyacrylamide resulted in a 90 % mesostructure in the MFI zeolite. Higher amounts of polymer had no positive effect on the mesoporous structure. The membrane demonstrated a high water flux (22 L m–2 h–1) with 99 % nickel and 93 % chromium rejection, and effective nitrate rejection (up to 34 %). Increasing the total dissolved solids from 1 to 1000 µA A–1 led to a 50 % increase in water flux. Additionally, raising the pressure by 2 bar resulted in an 80 % increase in the water flux and 15 % improvement in nitrate rejection.

Tailoring the pore structure、morphology and acidity of MFI zeolites by the regulation of Si/Al ratio in the synthetic gel

In this work, we report a facile and low-cost approach for controllable preparation of hierarchical mesoporous MFI zeolites via simply manipulating the Si/Al ratio in the initial synthetic precursor. The results demonstrate that Si/Al ratio significantly influences not only the acidity but also the pore structure as well as morphology of MFI zeolites. With the increase of Si/Al ratio, the mesoporous structures are weakened due to the increasingly severe crystal fusion leading to the formation of bulk zeolite crystal and the acid amounts decrease as well. The optimal sample Z-55 with spherical morphology is composed of numerous superfine nanocrystals. These primary results are quite beneficial to guiding reasonable design of the zeolites with other topologies. In LDPE cracking, the sample Z-55 with tri-modal mesopores distributions performs enhanced catalytic activity compared with convention MFI zeolite and the T50 is reduced to 391 °C, mainly ascribed to the luxuriant mesoporous structures.

Influence of catalyst pelletization on propane dehydrogenation over hierarchical MFI zeolite supported with platinum-yttrium nanoparticles

Platinum-yttrium (PtY) nanoparticles supported on a siliceous form of mesoporous MFI zeolite (MZ) were recently found to exhibit excellent catalytic performance in propane dehydrogenation (PDH). Herein, potential shaping of the PtY/MZ catalyst is investigated from the laboratory-synthesized powder form into industrially preferable pellets. The MZ zeolite powder was synthesized using multi-ammonium surfactants as a structure-directing agent and then pelletized in a hydraulic press by itself or with inorganic binders (i.e., pseudoboehmite, fumed silica, or hydrotalcite). As a part of the sequential pelletization process, pressing was followed by a high-temperature treatment (923 K). Addition of 20 wt% pseudoboehmite resulted in the highest mechanical strength without a significant loss of the initial zeolite mesoporosity. The pseudoboehmite-bound pellet also showed high catalytic activity and longevity in PDH application when simultaneously impregnated with 1 wt% Pt [Pt(NH3)4(NO3)2] and 1 wt% Y [Y(NO3)2·6H2O]. Notwithstanding the observed high propane conversion, the pseudoboehmite-bound catalyst produced an unsatisfactory result of low propylene selectivity (∼60%). Image analyses of HAADF-STEM EDS and solid-state 31P NMR spectroscopic data suggest that such findings could be attributed to Al migration from pseudoboehmite onto zeolite regime during the phase transformation of pseudoboehmite in the shaping process. Alternatively, the uses of non-acidic binders, such as fumed silica and hydrotalcite binders were also demonstrated. The silica-bound catalyst yielded high propane conversion with high propylene selectivity although mechanical strengths of the pellet were compromised to a moderate level.

Selective conversion of polyethylene wastes to methylated aromatics through cascade catalysis

Polyethylene was selective converted into methylated aromatics over the catalysts of aluminosilicate MFI zeolite nanosheets (s-ZSM-5) and mesoporous MFI zeolite modified with zinc species (Zn/meso-ZSM-5).

Sodium-free synthesis of mesoporous zeolite to support Pt-Y alloy nanoparticles exhibiting high catalytic performance in propane dehydrogenation

Mesoporous zeolite-supported Pt3Y catalyst deactivates slowly in propane dehydrogenation, maintaining high propane conversion and propylene selectivity, but the formation of the intermetallic compound requires atomistic migration of yttrium through silanol nests on the zeolite. Compared to the cumbersome generation of silanols via framework demetallation, we report a direct synthesis of mesoporous MFI zeolite possessing silanol nests. The synthesis procedure employed a diammonium-type bromide surfactant [C18H37N(CH3)2C6H12N(CH3)2C4H9Br2] and a sodium-free silica source. The basicity of the synthesis mixture was adjusted by the addition of readily available N(CH3)4OH, instead of converting the surfactant to hydroxyl form. The presence of silanol nests in the resultant zeolite was confirmed by IR and NMR spectroscopies. When the zeolite was supported with 0.50 wt% Pt and 0.50 wt% Y using nitrate precursors, a remarkably long catalytic lifetime of 20 days was obtained with high propane conversion and propylene selectivity under the reaction condition using neat propane gas at 853 K.

Highly dispersed Ni-La catalysts over mesoporous nanosponge MFI zeolite for low-temperature CO2 methanation: Synergistic effect between mesoporous and microporous channels

The mesoporous nanosponge MFI silicate zeolite was facilely fabricated by employing the long chain ammonium as the structure-directing agent. The zeolite with both mesoporous and microporous channels were selected as the support of Ni-La catalysts for methanation of CO2. Various techniques were used to characterize the catalysts systematically. The effects of the La2O3 promotor and pore morphology of the support on the catalytic performance were carefully investigated. Our study demonstrated that La promoter could be beneficial to the increase of the surface basicity and the enhancement of the metallic Ni dispersion. This would intensify the processes of the CO2 chemisorption and H2 dissociation in CO2 methanation. Besides, we also found that the catalyst supported on mesoporous nanosponge MFI zeolite performed higher activity and better long-term stability than the reference catalysts supported on bulk MFI and MCM-48, suggesting that the synergistic effect between the mesoporous and microporous channels displayed unique advantages. Kinetic study revealed that both the nanosponge structure and La2O3 promoter contributed to decreasing the reaction activation energy. Therefore, the present highly dispersed Ni-La catalyst over mesoporous nanosponge MFI zeolite promised a potential catalyst candidate for low-temperature CO2 methanation reaction.

Library Creation of Ultrasmall Multi‐metallic Nanoparticles Confined in Mesoporous MFI Zeolites

AbstractThe development of materials integrated with ultrasmall multi‐metal nanoparticles (UMMNs) and mesoporous zeolite is a considerable challenge in chemistry and materials science. We designed a trifunctional surfactant, in which the pyridyl benzimidazole in the hydrophobic tail generates the mesopores through π–π stacking; the diquaternary ammonium in the hydrophilic headgroup direct the formation of MFI zeolite sheets and the nitrogen atoms in the heterocyclic rings coordinate with various metal ions to form UMMNs confined in the zeolite matrix after calcination and reduction. A library of 56 UMMNs confined within both micropores and mesopores of MFI zeolites (MMZs) with 4 mono‐, 14 bi‐ and 38 tri‐metallic nanoparticles (sizes of 1.3–4.7 nm) of combinations of Rh, Pd, Pt, Au, Fe, Co, Ni, Cu and Zn were made. An improved catalytic performance was exhibited in the sequence of Rh‐MMZ<Rh/Pt‐MMZ<Rh/Pt/Ni‐MMZ for the mild oxidation of methane to methanol or liquid acid.

Library Creation of Ultrasmall Multi-metallic Nanoparticles Confined in Mesoporous MFI Zeolites.

The development of materials integrated with ultrasmall multi-metal nanoparticles (UMMNs) and mesoporous zeolite is a considerable challenge in chemistry and materials science. We designed a trifunctional surfactant, in which the pyridyl benzimidazole in the hydrophobic tail generates the mesopores through π-π stacking; the diquaternary ammonium in the hydrophilic headgroup direct the formation of MFI zeolite sheets and the nitrogen atoms in the heterocyclic rings coordinate with various metal ions to form UMMNs confined in the zeolite matrix after calcination and reduction. A library of 56 UMMNs confined within both micropores and mesopores of MFI zeolites (MMZs) with 4 mono-, 14 bi- and 38 tri-metallic nanoparticles (sizes of 1.3-4.7 nm) of combinations of Rh, Pd, Pt, Au, Fe, Co, Ni, Cu and Zn were made. An improved catalytic performance was exhibited in the sequence of Rh-MMZ<Rh/Pt-MMZ<Rh/Pt/Ni-MMZ for the mild oxidation of methane to methanol or liquid acid.

Direct synthesis of hierarchical zeolites through mesoporous 3D wormhole framework using single-head quaternary ammonium salt as structure-directing agent

Hierarchical aluminosilicate zeolites with uniform mesoporosity were successfully synthesized by one-stage crystallization under constant temperature with a novel single-head quaternary ammonium salt ([C18H37–N+(CH3)2–C6H12–N(CH3)2]Br−) as mesoporogen and structure-directing agent (SDA). Through precisely controlling the molar ratio of Si/Al and synthetic time, the mesoporous 3D wormhole framework (MCM-48) and crystalline microporous MFI structure were simultaneously constructed, revealed by a series of in-depth characteristic studies. Combining the advantages of the significantly improved diffusion from the mesoporous MCM-48 and the strong framework acidity of the crystalline microporous MFI zeolite, the hierarchical aluminosilicate zeolites exhibited outstanding catalytic activity with good reusability towards bulky aldol condensation compared with the conventional meso- or microporous zeolites.

An Extrinsic-Pore-Containing Molecular Sieve Film: A Robust, High-Throughput Membrane Filter.

MFI type zeolites with 10-membered-ring pores (ca. 0.55 nm) have the ability to separate p-xylene (ca. 0.58 nm) from its bulkier isomers. Here, we introduced non-zeolitic micropores (ca. 0.6-1.5 nm) and mesopores (ca. 2-7 nm) to a conventional microporous MFI type zeolite membrane, yielding an unprecedented hierarchical membrane structure. The uniform, embedded non-zeolitic pores decreased defect formation considerably and facilitated molecular transport, resulting in high p-xylene perm-selectivity and molar flux. Specifically, compared to a conventional, crack network-containing MFI membranes of similar thickness (ca. 1 μm), the mesoporous MFI membranes showed almost double p-xylene permeance (ca. 1.6±0.4×10-7 mol m-2 s-1 Pa-1 ) and a high p-/o-xylene separation factor (ca. 53.8±7.3 vs. 3.5±0.5 in the conventional MFI membrane) at 225 °C. The embedded non-zeolitic pores allowed for decreasing the separation performance degradation, which was apparently related to coke formation.

An Extrinsic‐Pore‐Containing Molecular Sieve Film: A Robust, High‐Throughput Membrane Filter

AbstractMFI type zeolites with 10‐membered‐ring pores (ca. 0.55 nm) have the ability to separate p‐xylene (ca. 0.58 nm) from its bulkier isomers. Here, we introduced non‐zeolitic micropores (ca. 0.6–1.5 nm) and mesopores (ca. 2–7 nm) to a conventional microporous MFI type zeolite membrane, yielding an unprecedented hierarchical membrane structure. The uniform, embedded non‐zeolitic pores decreased defect formation considerably and facilitated molecular transport, resulting in high p‐xylene perm‐selectivity and molar flux. Specifically, compared to a conventional, crack network‐containing MFI membranes of similar thickness (ca. 1 μm), the mesoporous MFI membranes showed almost double p‐xylene permeance (ca. 1.6±0.4×10−7 mol m−2 s−1 Pa−1) and a high p‐/o‐xylene separation factor (ca. 53.8±7.3 vs. 3.5±0.5 in the conventional MFI membrane) at 225 °C. The embedded non‐zeolitic pores allowed for decreasing the separation performance degradation, which was apparently related to coke formation.

Mesopore-selective incorporation of strong Brønsted acid catalytic sites via aluminium grafting on hierarchically porous siliceous MFI zeolite

Abstract Post-synthetic Al grafting onto the surface silanols in mesoporous MFI zeolite has been investigated in an attempt to obtain a model catalytic material that possesses strong Bronsted acid sites at mesopore surfaces of the zeolite, but not inside the microporous framework. To this end, a siliceous MFI zeolite with a mesopore/micropore hierarchy was synthesized using a meso-micro dual structure-directing diammonium surfactant. The hierarchically porous zeolite was treated with anhydrous AlCl3 for the formation of Si–O–Al bonding with silanols on the mesopore surfaces. According to solid-state 31P NMR spectroscopy of the surface-adsorbed phosphine oxides and catalytic activity for decalin cracking, the Al-grafting treatment performed in the conventional manner resulted in the formation of weak Bronsted acid sites, similar to Al grafting on SBA-15 mesoporous silica. To obtain strong Bronsted acid sites, we have developed a method of heating the AlCl3-grafted zeolite in a controlled-humidity chamber before calcination. The resultant zeolite was catalytically active for cracking of hydrocarbons requiring strong acid sites, but not for methanol-to-hydrocarbon conversion. The results support that the moisture treatment caused a local reconstruction of the initially grafted Al–O–Si framework portion to a strong Bronsted acid site. In addition, our model catalytic zeolite material unveiled the catalytic activity of Bronsted acid sites at the mesopore surfaces in hierarchically porous zeolite in n-octane cracking. Furthermore, we confirmed that this method was effective for other mesoporous MFI zeolites obtained through a post-synthetic desilication route.

Facilely fabricating highly dispersed Ni-based catalysts supported on mesoporous MFI nanosponge for CO2 methanation

Abstract The Ni-based catalysts were widely investigated as the catalysts toward CO2 methanation reaction because of their availabilities. However, compared with the noble metal based catalysts, the design and exploitation of Ni-based catalysts with outstanding low-temperature catalytic activities is still a big challenge. In order to solve this problem, the highly dispersed Ni catalysts had been facilely prepared by employing the basic amine functionalized mesoporous MFI nanosponge zeolite as the support. The functionalized amine group could induce the precisely regioselective precipitation of the Ni precursor in the mesoporous channels and the highly dispersed Ni nanoparticles were obtained. Besides, the La2O3 and MgO had been used to modify the surface basicity to further promote the low-temperature catalytic activities of the Ni-based catalysts. These catalysts were systematically measured by XRD, N2 physisorption, STEM, XPS, H2-TPR, and CO2-TPD. It was observed that the metallic Ni nanoparticles were homogenously distributed among the mesoporous channels. Furthermore, the La2O3 and MgO modification could obviously promote the surface basicity of the catalysts, which intensified the CO2 adsorption and activation. Thus, their apparent activation energies of CO2 methanation evidently decreased and their low-temperature activities were greatly promoted. Besides, it was also found that the thermal agglomeration of the Ni nanoparticles could be successfully inhibited via the confinement effect of the amine functionalized mesoporous channels, interpreting their excellent catalytic stabilities toward CO2 methanation.

Cascade reaction engineering on zirconia-supported mesoporous MFI zeolites with tunable Lewis-Brønsted acid sites: a case of the one-pot conversion of furfural to γ-valerolactone.

Catalytic cascade reactions are strongly desired as a potential means of combining multistep reactions into a single catalytic reactor. Appropriate catalysts composed of multi-reactive sites to catalyze cascade reactions in a sequential fashion are central to such efforts. Here, we demonstrate a bifunctional zeolite catalyst with close proximity of Brønsted and Lewis acid sites through the synthesis of a mesoporous ZrO2[Al]MFI nanosponge (NS). The unique mesopores of the MFI-NS allow the confinement of zirconium oxide clusters (Lewis acid sites, LA) within the few-unit-cell-thin MFI aluminosilicate zeolite wall (Brønsted acid sites, BA). Such a structure is clearly distinct from the conventional MFI zeolite, where the agglomeration of zirconium oxide clusters onto the external surface area within the crystal bulk is not possible, resulting in segregated BA and LA sites on the internal and external zeolite, respectively. By bringing the BA and LA within ZrO2[Al]MFI-NS 30, we uncovered a more efficient catalytic route for the conversion of furfural (100% within 2 h) to γ-valerolactone (GVL) (83%). This route is only evident when the long molecular diffusion path, in the most extreme case of physically mixed ZrO2-(LA) and Al-zeolites (BA) (45% of GVL yield), is eliminated. Unlike the bifunctional ZrO2–Al-beta (GVL yield of 75%), where the BA concentration is greatly compromised at the expense of LA formation, we also show that the ZrO2[Al]MFI-NS is able to maintain a high density and good stability of both types of acids.

Synthesis of mesoporous MFI zeolite via bacterial cellulose-derived carbon templating for fast adsorption of formaldehyde

Mesoporous ZSM-5 (MFI) zeolite was synthesized by using bacterial cellulose-derived activated carbon (BC-AC500) with a high surface area as a hard template. Different ratios of BC-AC500 and zeolite precursor gel were prepared in a Teflon-lined autoclave and crystallized at 180 °C for 48 h in a rotating oven. The physicochemical properties of the samples were characterized by x-ray diffraction (XRD), scanning/transmission electron microscopies (SEM/TEM), and N2 physisorption techniques. It was found that the mesoporous ZSM-5 zeolites have a specific surface area of 184-190 m2/g, a high mesopore volume of 0.120–0.956 ml/g and a wide pore size distribution ranging from 5 to 100 nm with a maximum at approximately 25.3 nm. The successfully made mesoporous ZSM-5 was tested as an adsorbent for formaldehyde adsorption in batch mode. The mesoporous ZSM-5 zeolite made from bacterial cellulose-derived activated carbon showed significantly faster adsorption kinetics than conventional ZSM-5 (0.0081 vs. 0.0007 g/mg min, respectively). The prepared material has an adsorption capacity of 98 mg/g and is highly reusable. The reported mesoporous ZSM-5 zeolites can be deployed for the rapid removal of toxic organics from wastewater when urgently needed, e.g., under breakthrough conditions.

Synergy of B and Al Dopants in Mesoporous MFI Nanocrystals for Highly Selective Alcoholysis of Furfuryl Alcohol into Ethyl Levulinate

In this article, the synergetic effect between the B‐ and Al‐based acidic sites in B–Al co‐doped mesoporous MFI nanocrystals (denoted as m‐B‐Al‐S1) is rationally applied to modify the alcoholysis process of furfuryl alcohol. The porosity and dopant concentration of the m‐B‐Al‐S1 materials are optimized via a modified Kirkendall growth method to boost the ultra‐high selectivity to ethyl levulinate reactions (94%). The m‐B‐Al‐S1 catalyst also shows good stability for further reuses.

Single-Crystalline MFI Zeolite with Sheet-Like Mesopores Layered along the a Axis.

Designing a templating strategy for directing mesopore growth along different crystallographic directions is essential for fabricating two- or three-dimensional single-crystalline mesoporous zeolites. However, so far, mesopores formed in MFI zeolites by soft templates have mostly been generated by disrupting growth along the b axis; generating mesopores by disrupting growth along the a axis is rare. Herein, a single-crystalline mesoporous MFI zeolite (SCMMZ) with sheet-like mesopores layered along the a and b axes was synthesized using a triply branched surfactant with diquaternary ammonium groups connected to 1,3,5-triphenylbenzene by a six- and eight-carbon alkyl chain (TPB-6 and 8). The sheet-like mesopores were embedded in the MFI framework and were retained even after calcination. Molecular mechanics calculations provided evidence of low binding energy configurations of the surfactant that directed the growth of straight and zigzag channels along the b and a axes, respectively. The formation of nanosheets was attributed to the geometric matching of the arrangement of the aromatic groups to the zeolite framework.

Hierarchical MFI Zeolites with a Single-Crystalline Sponge-Like Mesostructure.

Single-crystalline sponge-like MFI mesoporous zeolites (SSMZs) have been synthesized by using bolaform surfactants with an axial chiral binaphthyl core in the hydrophobic tail and triquaternary ammonium head groups, as bifunctional organic structure-directing agents (OSDAs). By changing the length of alkyl chain between a triquaternary ammonium head group and a binaphthyl group from 4 to 10 carbons, SSMZs with high specific surface area (382-434 m2 g-1 ), abundant micropore-mesopore connectivity, and uniform mesopore diameter (4-10 nm) were obtained. OSDAs with an alkyl chain length of 11 and 12 carbons led to the formation of nanorod-constructed mesoporous MFI zeolites. A geometrical matching between the cylindrical arrangement of the binaphthyl groups and the zeolitic framework is speculated to be the key factor for the formation of mesoporous zeolites. The SSMZ zeolites, with abundant mesopores beneficial for the diffusion of reactants, exhibited significantly higher catalytic efficiencies than those of the conventional ZSM-5 with a microcrystal morphology (≈1.5 μm).

Influence of iron aggregation on the catalytic performance of desilicated MFI in the DeNOx process

In the present study, an influence of the iron aggregation in conventional and micro-mesoporous MFI on their catalytic activity in the NO reduction with ammonia (DeNO x process) was studied. Modification of MFI zeolite properties was done by the desilication in the presence of NaOH and TPAOH (tertapropylammonium hydroxide). In the next step, the samples were modified with iron by ion-exchange with the use of a conventional solution of Fe cations (FeSO 4 ) and a solution of iron triple-metallic aggregates (oligocations) ([Fe 3 (OAc) 6 O(H 2 O) 3 ] + ). Both of the applied modification techniques (desilication and modification with Fe 3 oligocations) increased the catalytic activity of the MFI zeolite in the DeNO x process. This increased catalytic activity was connected with changes in sample porosity, Si/Al ratio, topology, as well as aggregation and dispersion of iron species on the catalyst surface, which was investigated by N 2 -sorption, XRD, ICP, NMR, HRTEM and UV-vis-DRS techniques. • Mesoporous MFI zeolite prepared by desilication. • New method of zeolites modification by triple-metalic oligocations. • Influence of zeolite porosity, Si/Al ratio, and the used iron precursor on the amount, aggregation and dispersion of the iron species on the catalyst surface. • High catalytic activity and selectivity to nitrogen in the DeNOx process of the samples modified by desilication and with Fe3 oligocations.