Zeolite Crystals Research Articles

Encapsulating Pt clusters during the crystallization of MWW zeolite

Directly encapsulation of Pt clusters within MWW zeolite was realized by precisely regulating the synthetic parameters, especially the alkalinity and the Pt content during the hydrothermal synthesis. Simple addition of Pt(NH3)4(NO3)2 to the routine recipe for MWW synthesis resulted in a mixture of MWW to FER zeolites, while appropriately lowering the alkalinity of the initial gel composition favored the formation of pure MWW phase and simultaneously the incorporation of Pt clusters into the micropores of MWW (Pt/Na/Al2O3/H2O/HMI/SiO2 = 0.0015/0.18/0.044/15/0.34/1). At high Pt loading (Pt/SiO2>0.00225), however, the crystallinity decreased considerably and the 3D MWW structure gradually evolved into disordered layers, while Pt particles located on the surface of the disordered layers and were prone to grow into larger ones. In short, addition of Pt(NH3)4(NO3)2 in the initial gel altered the crystallization process of MWW zeolite, and Pt-MWW could be obtained by appropriately lowering the alkalinity and accurately controlling the amount of platinum.

Hydrothermal Synthesis of Mordenite Type Zeolite

Zeolite is a crystalline alumino-silicate microporous material, which has been widely used as ion-exchangers, adsorbent and catalyst.
 Recently, several researches highlights the progress of zeolite-based catalysts in the CO2 conversion to valuable products.
 In the present work, hydrothermal synthesis of mordenite zeolite crystals, with composition of the chemical products Al2O3, 12.5 SiO2,2.4 NaOH, 110 H2O at 160°C for 96 hours (4 days) at Ph 11 is described. 
 Results of characterization of the mordenite zeolite by XRD, FTIR, EDAX, SEM, TGA, are presented and discussed.
 In the present work, hydrothermal synthesis and characterization of mordenite zeolite crystals is described.

Study on the synthesis and properties of porous cadmium zeolitic imidazolate framework for environmental treatment

In this study, cadmium imidazolate frameworks were synthesized by a solvothermal method from cadmium acetate and 2-methylimidazole in an ethanol/methanol mixture. The Cd(Im)2 processed at 150 oC after 8 hours with the mixture of solvents has high crystallinity. The appearance of the absorption band at 407.73 cm-1 shows a link formation of Cd (II) and N within HIm’s molecule. Cadmium imidazolate only formats zeolite crystal, the network fibers were potent, and the pores were alike. The dimension of pores is approximately 200 nm. The XRD diagram shows that the Cd(Im)2 has high crystallinity. The Cd(Im)2 phase is obvious from reflections at 7o, 10o, 12o, 14o, 15,6o and 17o. The surface area of Cd(Im)2 was 662.894 m2/g or 858.389 m²/g with BET or Langmuir calculations, respectively. The maximum adsorption capacity of Cd-ZIF-8 for the RhB is 64.52 mg.g-1, and the adsorption data were fitted well with a pseudo-second-order model.

Preparation and characterization of ZSM-5 zeolite

Recently, zeolites attracted considerable research attention because they exhibit adsorption properties, ion exchange capabilities and a good catalytic property, a specific pore size distribution; a unique chemical and thermal properties and several applications. 
 Actually zeolites play a crucial role as a catalyst to capture and convert Carbone dioxide into valuable products.
 In the present work, hydrothermal synthesis of ZSM-5 zeolite crystals, with composition of the chemical products 0.01 Al2O3,1SiO2,2 NaOH, 0.15 TPABr, 18.34 H2O at 170°C for 48 hours (2 days) at Ph 11 is described. 
 Results of characterization of the ZSM-5 zeolite by XRD, FTIR, EDAX, SEM, TGA, are presented and discussed.

Perspective on the Use of Ultrasonic Monitoring for In Situ Diagnostics of Zeolite and MOF Crystallization

Perspective on the Use of Ultrasonic Monitoring for In Situ Diagnostics of Zeolite and MOF Crystallization

Zeolite fixed cobalt–nickel nanoparticles for coking and sintering resistance in dry reforming of methane

Dry reforming of methane (DRM) displays a crucial role in CO2 fixation, but the current catalysts suffer from deactivation from thermodynamically oriented coking and metal sintering. Herein, we reported a catalyst by fixing the cobalt–nickel nanoparticles within the zeolite crystals (CoNi@zeolite), where the SiOx-O-Mδ+ (M = Ni or Co) linkage enhanced the reduction resistance of Co and Ni species compared with the generally supported catalysts, efficiently hindering the deep dehydrogenation of methane, which is well known as a reaction channel for coke formation. In addition, the rigid and thermally stable zeolite framework stabilized the cobalt–nickel nanoparticles to avoid their sintering during the reaction. As a result, the CoNi@zeolite catalyst exhibited a long reaction lifetime and great regenerability in a test for 980 h with reaction gas flow at 1200 L per unit mass of metal species per hour, outperforming conventionally supported metal catalysts. This work enables a proof-of-the-concept design of durable catalysts by zeolite fixation for the reactions in strongly reductive atmospheres.

An innovative approach based on microwave radiation for synthesis of zeolite 4A and porosity enhancement

Advantages of microwave radiation in terms of reducing reaction time and enhancing product quality were exploited for template-free zeolite 4A synthesis, in which a domestic microwave oven was purposely utilized instead of a scientific microwave reactor. Experimental data proved that the microwave-assisted hydrothermal synthesized product crystallized at the same phase as the zeolite obtained from the conventional hydrothermal method. Moreover, compared to the hydrothermal synthesis, microwave radiation considerably improves zeolite's properties, including forming more uniform and finer zeolite crystals. However, both synthesis methods produced zeolites with relatively limited surface areas. To solve this problem, an attempt to utilize microwave radiation as a post-washing technique gained a significant improvement of the zeolite's exposed surfaces that revealed effectiveness of microwave on removing the obstacles to release the blocked pores in the zeolite's structure. On that basis, the adsorption characteristics of the 4A zeolites prepared from the two synthesis methods were studied in consideration of the influence of post-washing steps. A comparison on adsorption of these materials was carried out in treating a synthetic dye-containing wastewater of which methylene blue (MB) was used as a model compound. Experiments showed an increment of about quadruple MB uptake achieved from the microwave-assisted method in comparison to the conventional route.

Unexpected high CO2 over C2H2 separation performance by high-silica CHA zeolite membranes

Energy-efficient CO2/C2H2 separation by membranes is critical for producing acetylene by partial combustion of natural gas. Separating CO2 and C2H2 by membranes is challenging because they have the same kinetic diameter and similar dimensions. Here we demonstrate for the first time high-silica chabazite (CHA) zeolite membranes with surprisingly high CO2 selectivity over C2H2. Both unary permeation and binary mixture permeation data demonstrated consistent high CO2 permselectivity >30. Equilibrium adsorption isotherms indicate only a slight adsorption selectivity for C2H2, implying that a high diffusion selectivity for CO2 is required for the effective separation. The dynamic uptake data, however, points to slight C2H2 diffusion selectivity in CHA zeolite crystals. Hypotheses are proposed to explain the inconsistency between crystal and membrane diffusion results.

A Nanostrips-Assemble Morphology of ZSM-5 Zeolite for Efficient Propylene Production from Methanol Conversion

Turning the morphology and orientated growth of zeolite crystals is essential to alter their catalytic performances. MFI-type ZSM-5 nanostripes (named as D-Z5) with a sea-urchin-like overall morphology were directly synthesized with a commercially available and small-molecular organic structure-directing agent (OSDA) of 1-butyl-1-methylpyrrolidinium hydroxide. Their nanostrip crystals exhibited a unique dioriented morphology with thin thicknesses of ∼8 nm and ∼70 nm along the a-axis and b-axis, respectively. The dealuminated D-Z5 displayed higher propylene selectivity (∼57%), longer lifetime (60 h) and much higher propylene-to-ethylene ratio (>12) in methanol-to-propylene (MTP) reaction than those conventional ZSM-5 with known crystal morphologies. Computational simulation and experimental measurements provided solid proof that the diorientated crystals decreased the bulky molecular diffusion resistance, postponed the secondary reaction and then promoted propylene to diffuse rapidly out of two sets of micropores in zeolites. This unusual diorientation phenomenon is not only beneficial for improving the MTP catalytic performance of ZSM-5, but also expected to be versatile to develop other useful zeolite catalysts.

Tuning High-Density Polyethylene Hydrocracking through Mordenite Zeolite Crystal Engineering

We investigate the hydrocracking of high-density polyethylene using a bifunctional Pt/Al2O3 and modified mordenite acid catalyst. Mass transport limitations impact polymer diffusion into the mordenite pore complex. Initial reaction intermediates are formed on the zeolite’s outer surface. Intercrystallite open-end mesopores improve the diffusion of reaction intermediates deeper into the crystal. Recrystallization and desilication of mordenite lead to a higher polymer conversion and shift the product distribution maximum from pentanes to hexanes and heptanes. The nature of mesopores (occluded or open) and total Brønsted acidity significantly impact zeolite activity and selectivity.

Consequences of metal-acid site proximity for alkane isomerization and β-scission mediated by bifunctional catalytic cascades

Bifunctional isomerization and β-scission of alkanes involve kinetic cascades mediated by alkenes that form at a (de)hydrogenation function that resides within diffusion distances from the acid function at which alkenes react. Such distances matter for reactivity and selectivity, especially within voids of molecular dimensions, because of gradients in reactant and product concentrations within acid domains. Dispersing Pt nanoparticles within zeolite crystals places the two functions within nanometer distances, instead of the larger distances prevalent when the Pt function resides outside zeolite crystals. Such intimacy leads to higher n-heptane conversion turnover rates (per H+) and shifts selectivities towards primary isoalkanes, most evidently on medium-pore zeolites (MFI), because confinement effects lead to slower diffusion and higher intrinsic H+ reactivity than in larger-pore zeolites, and for shorter Pt-H+ distances, which define the dimensions of the acid domain. Intracrystalline Pt nanoparticles do not affect the number or intrinsic properties of the metal or acid functions or introduce reaction channels mediated by more reactive (but less abundant) diene intermediates, as demonstrated here by reactive probes of metal (CO oxidation) and acid (CH3OH dehydration) functions, infrared spectra of OH groups and chemisorbed CO, kinetic effects of H2 pressures, and transition state energies from density functional theory. Metal-acid distances influence the requisite kinetic cascades instead through the formation and scavenging of reactants and intermediates along the isomerization-scission sequence in the presence of significant gradients in their concentrations. Reaction-transport treatments show that such gradients weaken with increasing intracrystalline densities of Pt nanoparticles (and consequent smaller acid domains), thus circumventing isoalkene equilibration and local thermodynamic bottlenecks through hydrogenation of the primary isoalkene products. Such scavenging inhibits the formation of dimethylpentenes, which act as required precursors to β-scission products, leading to higher selectivities to isoalkanes as Pt-H+ distances decrease. These data and reaction-transport formalisms resolve persistent controversies about the chemical or diffusional origins of rate and selectivity consequences of the location of a metal function. They demonstrate the essential, but often neglected, need to determine the precise location of the metal function and to develop reaction-transport treatments to describe rates and selectivity in bifunctional metal-acid catalysis.

Microreactor for the characterization of zeolite hydrothermal synthesis by small angle X-ray scattering (SAXS)

During zeolite synthesis, exploring the growth of nanoparticles is crucial for studying the crystallization mechanism. Synchrotron radiation small angle X-ray scattering (SAXS) is a powerful technique for the in-situ characterization of zeolite crystallization. Herein, a microreactor was developed for use at the Beijing Synchrotron Radiation Facility (BSRF) to achieve the in-situ SAXS characterization of the nucleation and growth of zeolite crystallization. The results show that the fractal structure convert from surface fractal during induction nucleation to mass fractal during crystal growth. The surface fractal dimension first fluctuated slightly and increased rapidly, while the mass fractal dimension gradually increased, reflecting the particle growth. This work provides important information for further exploring zeolite crystallization.

Micro- and Nanoscale Heterogeneities in Zeolite Beta as Measured by Atom Probe Tomography and Confocal Fluorescence Microscopy.

Micro- and nanoscale information on the activating and deactivating coking behaviour of zeolite catalyst materials increases our current understanding of many industrially applied processes, such as the methanol-to-hydrocarbon (MTH) reaction. Atom probe tomography (APT) was used to reveal the link between framework and coke elemental distributions in 3D with sub-nanometre resolution. APT revealed 10-20 nanometre-sized Al-rich regions and short-range ordering (within nanometres) between Al atoms. With confocal fluorescence microscopy, it was found that the morphology of the zeolite crystal as well as the secondary mesoporous structures have a great effect on the microscale coke distribution throughout individual zeolite crystals over time. Additionally, a nanoscale heterogeneous distribution of carbon as residue from the MTH reaction was determined with carbon-rich areas of tens of nanometres within the zeolite crystals. Lastly, a short length-scale affinity between C and Al atoms, as revealed by APT, indicates the formation of carbon-containing molecules next to the acidic sites in the zeolite.

Engineering Lewis Acidity in Zeolite Catalysts by Electrochemical Release of Heteroatoms during Synthesis.

The creation of heteroatom nodes in zeolite frameworks is a challenging but rewarding pathway to superior materials for numerous catalytic applications. Here, we present a novel method for precise control over heteroatom incorporation by in situ anodic release of a desired metal during hydrothermal zeolite synthesis. The generic character of the technique and the applicability of the new synthesis reactor are shown across 3 zeolite structures crystallized and 4 electrode metals in two pH zones and by offering access to a new mixed-metal zeolite. The timed and voltage-controlled metal release offers a minimized interference between the metal precursor state and critical events in the zeolite's crystallization. A mechanistic study for Sn-MFI revealed the key importance of controlled release: while keeping its concentration lower than in batch, a lot more Sn can be incorporated into the framework. The method grants access to 10× increased framework Lewis acid site densities (vs batch controls) for the most relevant stannosilicates. As a proof, the electro-made materials demonstrate higher productivity than their classic counterparts in lactate catalysis. This innovative approach effectively expands the synthesis space of zeolites.

Microwave synthesis of zeolite X from bituminous fly ash and its characterization

This research studied the synthesis of zeolite X from bituminous fly ash (BFA) using microwave heating process. The Si and Al was extracted from BFA using 3 M NaOH at 75 °C for 24 h and adjusted the molar ratio of Si/Al in the filtrate with Na2AlO3 solution. The synthesis temperature of the filtrate (65–115 °C), time (10–90 min) and NaOH concentration (0–3 M) were investigated. QXRD results showed that zeolite X were obtained at the highest quantity of 91.8% under the microwave heating at 95 °C for 60 min without the addition of NaOH during the preparation of Na2AlO3 solution. BET analysis showed that the surface area of the synthesized zeolite X was 288.9 m2/g with pore volume and size of 0.156 cm3/g and 2.16 nm, respectively. SEM images reveals the appearance of octahedral crystal of zeolite X with the presence of minimal amount of irregular shape of zeolite X.

Synthesis of hierarchical porous ceramsites loaded with GIS-P1 zeolite crystals for removal of ammonia nitrogen from aqueous solution

In this study, ceramsites loaded with GIS-P1 zeolite were prepared via high-temperature sintering and hydrothermal synthesis using fly ash as the raw materials. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used to confirm the structure of the ceramsites; moreover, the transformation mechanism of zeolite was studied by Fourier transform-infrared and Raman spectroscopy. The specific surface area of zeolitization ceramsites increased to 40.86 m2/g from 0.59 m2/g of the basic ceramsites. The results showed that the removal rate was 93.6% for NH4+−N aqueous solution with an initial concentration of 50 mg/L. The results of kinetic and isothermal fitting showed that the adsorption process of NH4+−N by zeolitization ceramsites coexisted between physical and chemical adsorption. Furthermore, the results of density functional theory calculations and X-ray photoelectron spectroscopy analysis showed that ion exchange and pore adsorption were the main adsorption mechanisms of the zeolitization ceramsites. This study provides a new method to significantly improve zeolite ceramsites with large specific surface areas, which can easily separate NH4+−N from water. Moreover, it can realize the environmental protection purpose of “wastes-treat-wastes.”

Conversion of Methanol into Hydrocarbons over Biomass‐Assisted ZSM‐5 Zeolites: Effect of the Biomass Nature

AbstractBiomass waste was revealed to act as a promising bio‐template to modify and possibly tailor the zeolite intrinsic properties: texture, crystallinity and acidity. According to the “bio‐sourced secondary template (BSST)” concept, 7 types of abundant biomasses (lignin, oxidized lignin, coffee bagasse, spent tea leaves and three kinds of algae) were selected and their role was evaluated in the zeolite crystallization. As‐synthesized biomass‐assisted ZSM‐5 zeolites were characterized by XRD, SEM, BET and NH3‐TPD techniques to investigate the effects of biomass extra‐addition. The results showed that mainly surface acidic properties were impacted by the presence of biomass. Among them, spent tea leaves‐mediated ZSM‐5 (named A‐tea) exhibited a high catalytic performance in the methanol‐to‐olefins reaction (MTO), with full methanol conversion for more than 50 h at 83 % selectivity towards light olefins, probably due to its mild acidity. Besides, more acidic ZSM‐5 zeolites obtained using three algae (algaCM, algaTM and algaBB), according to the B‐method, demonstrated a methanol conversion superior to 50 % during 75, 94 and 134 h, respectively. This study led to synthesize potential catalysts exhibiting a high MTO catalytic performance, as well as providing hints for future investigations aiming to control zeolite nucleation and growth following the BSST strategy.

Effect of Particle Size on the Sodium Ions Utilization Efficiency of Zeolite-Templated Carbon as the Anode in a Sodium Ion Battery

A series of zeolite-templated carbon (ZTC) with particle sizes of 1 μm, 70 nm, and 10 nm have been prepared. The external surface area and diffusion path of Na+ inside the ZTC was varied by controlling the size of the zeolite crystals used as templates. The three ZTC samples have been used to store sodium cations (Na+) for the purpose of sodium-ion batteries (SIB). It was found that the ZTC with a particle size of 10 nm exhibited the highest first discharge capacity of 2116 mAh·g–1 at a current density of 0.1 mA·g–1 due to the highest external surface area and more complete filling of the internal pore volume of the ZTC. While the ZTC with 70 nm particle size showed better reversible capacity of 180 mAh·g–1 at a current density of 0.1 mA·g–1, and the 10 nm size ZTC caused more electrolyte decomposition reaction and more solid electrolyte interphase (SEI) layer on the external surface of the crystals, resulting in a low first Coulombic efficiency and poor Na+ extraction.

Alumina-embedded HZSM-5 with enhanced behavior for the catalytic cracking of biomass pyrolysis bio-oil: Insights into the role of mesoporous matrix in the deactivation by coke

The behavior of HZSM-5 zeolite embedded in γ-Al2O3/α-Al2O3 matrix in the catalytic cracking of biomass pyrolysis bio-oil was studied with special focus on the role of the matrix in the deactivation by coke. The runs were conducted at 450 ºC, space-time of 0.35 gzeolite.h.gfeed−1 and 0.5 h, 1 h, and 2 h on stream. The analysis of reaction products was conducted by in-line GC and GC/MS, and deactivated catalyst samples were extensively characterized by N2 physisorption, NH3-TPD, TPD-TPO, TPD-GC/MS and LDI FT-ICR MS. The alumina-embedded catalyst (Cat−Z30) exhibited greater stability, keeping the bio-oil conversion above 88 % for 0.5 h on stream, in comparison to the bulk HZSM-5 that deactivated rapidly entailing a bio-oil conversion plunge (from 95 % to 40 %). Consequently, the yield of gasoline-range hydrocarbons (> 70 % MAH monoaromatics) was boosted from 18 % to 26 % for the same reaction time. The aqueous liquid byproduct concurrently produced has a suitable composition for H2 production by further steam reforming. The enhanced behavior was caused by the weak-acid mesoporous structure of the matrix playing a dual function: i) diffusive-shell (inwards) role by promoting fragmentation/deoxygenation of bulky molecules (e.g., saccharides and guaiacols) into reactive oxygenates, and deposition of thermally-induced coke away from the zeolite micropores; ii) spread-growth (outwards) role by enhancing the diffusion of hydrocarbons outwards from zeolite crystals, and by promoting the development of heavy polycyclic structures that delay the blockage of active sites in micropores. The results are useful to progress towards the integral valorization of raw bio-oil, the development of active and stable catalysts, and the proposal of regeneration strategies necessary for the scaling up.

An optimization of synthesis technique for Na-X zeolite from coal-fly ash using Taguchi experimental design

Na-X Zeolite was made from Class-F coal fly ash from a thermal power plant in the Indian state of Gujarat. The objective of this study is to maximize Na-X zeolite crystallization by using alkaline fusion hydrothermal treatment. The authors have also optimized the process variables using the L9 orthogonal Taguchi method. The operating parameters investigated are fusion temperature, fusion time, liquid/solid (L/S) ratio, and alkaline solution concentration. The XRF analysis of coal fly ash reveals that quartz (SiO2), mullite (Al2O3.SiO4), and a small fraction of hematite and magnetite are the major minerals. The highly crystalline zeolite (ZT-5) was synthesized in a 0.3 M NaOH solution at a fusion temperature of 550 °C for 12 h. with a 1.3 L/S ratio. Contrary to the CFA graph, the zeolite (ZT-5) XRD pattern displays prominent peaks between 20 and 40°. The SEM images illustrate the transition from a smooth spherical texture to a highly crystalline lattice structure in the morphology of zeolite. A sharp stretch around 440 and 460 cm−1 and weak bend around 660 and 694 cm−1 show the relative O-T-O deformation and the change in shape of the Al-O-H bonds, as measured by FT-IR absorption.