Synthesis and Catalytic Behavior of Ferrierite Zeolite Nanoneedles

Amino-Acid-Assisted Synthesis of Hollow Hierarchical FER Zeolite with Improved Catalytic Performance

Hierarchical zeolites are highly-desired catalysts in the petrochemical industry due to their shorter diffusion length, faster diffusion rate, and better accessibility to active acid sites compared with conventional zeolites. Herein, we report a simple amino-acid-assisted method to synthesize urchin-like hollow hierarchical FER zeolites with abundant mesopores and macroporous inner cavities. An amino acid (i. e. L-lysine) is used to facilitate the agglomeration of primary gel nanoparticles. The preferential nucleation and crystal growth at the external surfaces together with the lagged crystallization of the inner core of the agglomerates results in the formation of hollow inner cavities after the exhaustion of interior materials. Thanks to the unique hierarchical structure and more accessible acid sites, the hollow hierarchical FER zeolite exhibits improved catalytic performance over the conventional one in the skeletal isomerization of 1-butene to isobutene.

Intergrowth Zeolites, Synthesis, Characterization, and Catalysis

Microporous zeolites that can act as heterogeneous catalysts have continued to attract a great deal of academic and industrial interest, but current progress in their synthesis and application is restricted to single-phase zeolites, severely underestimating the potential of intergrowth frameworks. Compared with single-phase zeolites, intergrowth zeolites possess unique properties, such as different diffusion pathways and molecular confinement, or special crystalline pore environments for binding metal active sites. This review first focuses on the structural features and synthetic details of all the intergrowth zeolites, especially providing some insightful discussion of several potential frameworks. Subsequently, characterization methods for intergrowth zeolites are introduced, and highlighting fundamental features of these crystals. Then, the applications of intergrowth zeolites in several of the most active areas of catalysis are presented, including selective catalytic reduction of NOx by ammonia (NH3-SCR), methanol to olefins (MTO), petrochemicals and refining, fine chemicals production, and biomass conversion on Beta, and the relationship between structure and catalytic activity was profiled from the perspective of intergrowth grain boundary structure. Finally, the synthesis, characterization, and catalysis of intergrowth zeolites are summarized in a comprehensive discussion, and a brief outlook on the current challenges and future directions of intergrowth zeolites is indicated.

Improved Catalytic Performances of the NaOH-Treated ZSM-22 Zeolite in the 1-Butene Skeletal Isomerization Reaction: Effect of External Acid Sites

In this paper, a series of alkaline-treated ZSM-22 zeolite samples were prepared by treating the parent ZSM-22 zeolite using NaOH aqueous solution with different concentrations. By investigating the effects of alkaline treatment on the parent ZSM-22 zeolite, we discovered that the alkaline treatment contributed to the reduction of Brønsted acid sites due to the coverage of extra-framework Al on its external surface. In addition, it was found that the alkaline-treated samples were favorable to the improvement of the isobutene yield and selectivity, while these features appeared to be low for the subsequent acid-washed counterparts in the skeletal isomerization reaction of 1-butene. These results indicate that the catalytic performance of ZSM-22 zeolite is related to reduced amounts of Brønsted acid sites in it. To further reveal the reasons for the promoted catalytic performances of the alkaline-treated ZSM-22 series zeolites, we studied the properties of coke deposited on the two series of samples using Raman spectroscopy and thermogravimetric analysis and mass spectrometry (TG/MS-TPO). It was shown that the carbon deposited on the alkaline-treated series samples was mainly distributed at the outer surface, while the coke was distributed to a relatively lesser extent at the exterior surface for the acid-washed series samples. Moreover, by partially passivating outer acid sites of the parent zeolite, the selected alkaline-treated zeolite, and acid-washed zeolite, their isobutene selectivities were all improved with the decrease in outer acid sites. These phenomena confirmed that the improved catalytic performances of the alkaline-treated samples are related to their decreased external Brønsted acid site density, which further demonstrated that the high isobutene yield and selectivity in the skeletal isomerization reaction of 1-butene is realized via the monomolecular reaction pathway of 1-butene.

Tracking Structural Deactivation of H-Ferrierite Zeolite Catalyst During MTH with XRD

We used the methanol-to-hydrocarbon (MTH) reaction as a shape-selective model reaction to investigate coke formation in zeolite H-Ferrierite. Despite being a 2D topology in terms of channel propagation, the FER framework displays a lattice expansion in all three dimensions of space upon deactivation. Therefore, the volume of the unit cell is an excellent X-Ray diffraction (XRD) descriptor for the catalyst deactivation. A model with dummy atoms added, also proved to be an accurate approach to measure the amount of internal coke and/or water inside the pore network correlated with thermogravimetric analysis results. While the catalyst deactivation of the H-Ferrerite during the MTH was fast, a comparably long induction period was observed. We were able to track such fast deactivation with the aforementioned descriptors by means of an operando XRD study by a standard laboratory diffractometer.

Direct synthesis of ultrathin FER zeolite nanosheets via a dual-template approach

The synthesis of zeolites with nanosheet morphology has been attracting extensive attention. Despite the steady progress, the direct synthesis of ultrathin nanosheets of FER zeolite with thickness of less than 10 nm is still a great challenge. Herein we report a facile synthesis of FER zeolite nanosheets (named SCM-37) by using octyltrimethylammonium chloride (OTMAC) and 4-dimethylaminopyridine (4-DMAP) as dual organic templates. The effects of synthesis parameters, including initial molar ratio of SiO2/Al2O3, crystallization temperature and time were investigated. It turned out that the crystallization field of SCM-37 was narrow. A two-step crystallization method was utilized to obtain pure and completely crystallized SCM-37 zeolite. SCM-37 was characterized by multiple techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen physisorption, Fourier transform infrared (FTIR), ammonia-temperature programmed desorption (NH3-TPD) and nuclear magnetic resonance (NMR), and compared with the conventional FER zeolite (C-FER). The two most significant features of SCM-37 are the ultrathin crystal nanosheet and extremely high external surface area. The thickness of SCM-37 along the a-axis is 4∼7 nm, while that of C-FER is over 20 nm. The external surface area reaches 198 m2 g-1, which is over ten times larger than that of C-FER. The catalytic performances of the FER zeolites were evaluated by the cracking of 1,3,5-triisopropylbenzene (TiPB). Although possessing a lower amount of total acid sites, SCM-37 showed higher conversion of TiPB, as well as selectivity to the deep cracking products. The superior performance of SCM-37 was attributed to the higher external surface area arising from the ultrathin nanosheets.

Design of a Small Organic Template for the Synthesis of Self-Pillared Pentasil Zeolite Nanosheets

Zeolite nanosheets with excellent mass transfer are attractive, but their successful syntheses are normally resulted from a huge number of experiments. Here, we show the design of a small organic template for the synthesis of self-pillared pentasil (SPP) zeolite nanosheets from theoretical calculations in interaction energies between organic templates and pentasil zeolite skeletons. As expected, the SPP zeolite nanosheets with the thickness at 10-20 nm have been synthesized successfully. Characterizations show that the SPP zeolite nanosheets with about 90% MFI and 10% MEL structures have good crystallinity, the house-of-card morphology, large surface area, and fully four-coordinated aluminum species. More importantly, methanol-to-propylene tests show that the SPP zeolite nanosheets exhibit much higher propylene selectivity and longer reaction lifetime than conventional ZSM-5 zeolite. These results offer a good opportunity to develop highly efficient zeolite catalysts in the future.

Enhanced Selectivity and Stability of Finned Ferrierite Catalysts in Butene Isomerization

Designing zeolite catalysts with improved mass transport properties is crucial for restrictive networks of either one- or two-dimensional pore topologies. Here, we demonstrate the synthesis of finned ferrierite (FER), a commercial zeolite with two-dimensional pores, where protrusions on crystal surfaces behave as pseudo nanoparticles. Catalytic tests of 1-butene isomerization reveal a 3-fold enhancement of catalyst lifetime and an increase of 12 % selectivity to isobutene for finned samples compared to corresponding seeds. Electron tomography was used to confirm the identical crystallographic registry of fins and seeds. Time-resolved titration of Brønsted acid sites confirmed the improved mass transport properties of finned ferrierite compared to conventional analogues. These findings highlight the advantages of introducing fins through facile and tunable post-synthesis modification to impart material properties that are otherwise unattainable by conventional synthesis methods.

Pinpointing and Quantifying the Aluminum Distribution in Zeolite Catalysts Using Anomalous Scattering at the Al Absorption Edge

The location of aluminum in a zeolite framework structure defines the accessibility and geometry of the catalytically active sites, but determining this location crystallographically is fraught with difficulties. Typical zeolite catalysts contain only a small amount of aluminum, and the X-ray scattering factors for silicon and aluminum are very similar. To address this problem, we have exploited the properties of resonant X-ray powder diffraction across the Al K edge, where the aluminum scattering factor changes dramatically. By combining conventional synchrotron powder diffraction data with those collected at energies near the X-ray absorption edge, aluminum is highlighted. In this way, the different distributions of aluminum in two FER-type zeolites with identical chemical compositions but different catalytic properties could be determined unambiguously. The results are consistent with previous studies, but quantitative. This approach constitutes a major advance in our fundamental understanding of the relationship between zeolite structure and catalytic activity.

A Cooperative OSDA Blueprint for Highly Siliceous Faujasite Zeolite Catalysts with Enhanced Acidity Accessibility

A cooperative OSDA strategy is demonstrated, leading to novel high-silica FAU zeolites with a large potential for disruptive acid catalysis. In bottom-up synthesis, the symbiosis of choline ion (Ch⁺ ) and 15-crown-5 (CE) was evidenced, in a form of full occupation of the sodalite (sod) cages with the trans Ch⁺ conformer, induced by the CE presence. CE itself occupied the supercages along with additional gauche Ch⁺ , but in synthesis without CE, no trans was found. The cooperation, and thus the fraction of trans Ch⁺ , was closely related to the Si/Al ratio, a key measure for FAU stability and acidity. As such, a bottom-up handle for lowering the Al-content of FAU and tuning its acid site distribution is shown. A mechanistic study demonstrated that forming sod cages with trans Ch⁺ is key to the nucleation of high-silica FAU zeolites. The materials showed superior performances to commercial FAU zeolites and those synthesized without cooperation, in the catalytic degradation of polyethylene.

Advances in the Synthesis of Ferrierite Zeolite

As one of the most important porous materials, zeolites with intricate micropores have been widely employed as catalysts for decades due to their large pore volume, high surface area, and good thermal and hydrothermal stabilities. Among them, ferrierite (FER) zeolite with a two-dimensional micropore structure is an excellent heterogeneous catalyst for isomerization, carbonylation, cracking, and so on. In the past years, considering the important industrial application of FER zeolite, great efforts have been made to improve the synthesis of FER zeolite and thus decrease the synthesis cost and enhance catalytic performance. In this review, we briefly summarize the advances in the synthesis of FER zeolite including the development of synthesis routes, the use of organic templates, organotemplate-free synthesis, the strategies of morphology control, and the creation of intra-crystalline mesopores. Furthermore, the synthesis of hetero-atomic FER zeolites such as Fe-FER and Ti-FER has been discussed.

Depicting the crystal structure of fibrous ferrierite from British Columbia using a combined synchrotron techniques approach

The ferrierite crystal structure has often been subject to discussion because of the possible lowering of symmetry from the space group Immm. It mainly occurs in nature with a fibrous crystal habit, and because of the existence of line/planar defects in the framework, texture and preferred orientation effects it has been difficult to obtain an exact crystallographic model based only on the results from powder diffraction data. Therefore, nano-single-crystal diffraction and tomography data have been combined in order to improve the refinement with a meaningful model. High-quality single-crystal data, providing reliable structural information, and tomography images have been used as input for a Rietveld refinement which took into account a phenomenological description of stacking disorder and the analytical description of the preferred orientation, by means of spherical harmonics for strong texture effects. This is one of the first examples of application of synchrotron nano-diffraction for the structure solution of fibrous minerals of micrometre to nanometre size. The high quality of the crystals allowed collection of single-crystal X-ray diffraction data of up to 0.6 Å resolution, leading to an unambiguous solution and precise anisotropic refinement. Nano-single-crystal diffraction and phase contrast tomography data were collected at ID11 and the high-resolution powder diffraction patterns at ID22 of the European Synchrotron Radiation Facility. This detailed crystallographic characterization provides a basis for understanding the potential of ferrierite for toxicity and carcinogenicity.

Interconnected Pd Nanoparticles Supported on Zeolite-AFI for Hydrogen Detection under Ultralow Temperature

The stability for a hydrogen sensor is of crucial importance under a low-temperature range (e.g., 200-400 K), especially in critical environments (e.g., aerospace). However, the "reverse sensing behavior" of Pd-based sensing materials at low temperatures limits their wide application. Herein, a three-dimensional (3D) hydrogen-sensing material of interconnected Pd nanoparticles supported on zeolite-AFI (zeolite-AFI@Pd NPs) is designed for the hydrogen sensor at low temperature. The interconnected Pd NPs of ∼15 nm in diameter are achieved onto the zeolite-AFI framework by reduction-controlled self-assembly growth, followed by partially etching-off zeolite. The 3D structure provides a larger surface ratio for improving hydrogen adsorption onto Pd, and more space for PdHx intermediate expansion, which effectively facilitates response to hydrogen and suppresses the α-β phase transition. Remarkably, there is no "reverse sensing behavior" observed in zeolite-AFI@Pd NPs, though temperature is as low as to 200 K compared with that of pristine Pd nanowires at 287 K. Furthermore, the zeolite-AFI@Pd NPs sensors yield excellent sensing response and high stability to hydrogen at temperature from 200 to 400 K. Such Zeolite-AFI@Pd NPs sensors are expected to detect hydrogen leakage, especially in critical environments of low temperature.

A versatile mono-quaternary ammonium salt as a mesoporogen for the synthesis of hierarchical zeolites

Here we report a versatile method to synthesize hierarchically porous zeolites with FER, CHA and MFI topologies by using inexpensive mono-quaternary ammonium N-cetyl-N-methylpyrrolidinium (C₁₆NMP) bromide as a mesoporogen.

Conformation of intrazeolitic choline ions and the framework topology of zeolite hosts

A close relationship between the conformation of choline and the structure type of zeolites crystallized using this organic species was found.

The host–guest interactions in as-made zeolites Y, UZM-4, UZM-22, offretite, ferrierite, phillipsite, EU-12 and levyne, all of which were synthesized using choline as an organic structure-directing agent, have been investigated by a combination of different experimental techniques, including Raman, ¹H-¹³C CP MAS NMR and variable-temperature IR spectroscopies, together with theoretical calculations. The conformation of this asymmetric quaternary ammonium cation was shown to differ significantly according to the pore topology of the zeolite host and the intrazeolitic location of the organic guest molecule. Theoretical calculations using the pure-silica zeolite model reveal that among its three representative conformers (i.e., gauche, trans and trans′ forms), the conformer, which was experimentally found to dominantly or exclusively exist in zeolite structures studied, always has a lower interaction energy with the surrounding zeolite framework. Our work provides the first example in which the conformation of organic structure-directing agents plays an important kinetic role in governing the phase selectivity during zeolite nucleation.

Designing ferrierite-based catalysts with improved properties for skeletal isomerization of n-butene to isobutene

The crystal morphology and size of ferrierite catalysts were controlled by a suite of crystallization methods and structure-directing agents.

Synthesis of hierarchical ferrierite using piperidine and tetramethylammonium hydroxide as cooperative structure-directing agents

Zeolite ferrierite aggregates with hierarchical porosity were synthesized using TMAOH and piperidine as cooperative structure-directing agents (co-SDAs).