MFI-type Zeolite Research Articles

Role of Hydroxyl Groups in Zn-containing Nanosized MFI Zeolite for the Photocatalytic Oxidation of Methane.

The effective conversion of methane to a mixture of more valuable hydrocarbons and hydrogen under mild conditions is a significant scientific and practical challenge. Here, we synthesized Zn-containing nanosized MFI zeolite for direct oxidation of methane in the presence of H2O and air. The presence of the surface hydroxyl groups on nanosized MFI-type zeolite and their significant reduction in the Zn-containing nanosized MFI zeolite were confirmed with Infrared Fourier Transform (FTIR) spectroscopy. Incorporation of zinc atoms into the framework of nanosized MFI zeolite is revealed by Nuclear Magnetic Resonance, X-ray Diffraction and UV-Vis Spectroscopy. Unexpectedly, pure silica MFI zeolite exhibited the highest photocatalytic performance. Our findings demonstrated that large number of isolated silanol groups and silanol nests increase the formation of ⋅OH, and enhance the productivity of oxygenate compounds and C2H6, while the Zn incorporated into the zeolite framework or attached to the silanol nests of the nanosized zeolites are less efficient. A mechanism of photocatalytic methane oxidation is proposed. These findings provide insights into the development of active nanosized zeolite photocatalysts with an extended amount of surface hydroxyl groups that can play a key role in photocatalytic methane conversion.

From cassava peel (Manihot esculenta) to hydrocarbon-rich bio-oil: Catalytic flash pyrolysis as a new valorization route

The valorization of agroindustrial residues for second-generation biofuels has garnered attention due to the increasing demand for low-carbon fuels aligned with transportation sector decarbonization efforts. In this context, cassava processing residues, particularly cassava peel, remain largely unexplored but offer a cheap, abundant, and renewable feedstock that can be converted into hydrocarbon-rich biofuel. Thus, the originality of this study lies in investigating the selective conversion of cassava peel into renewable aromatic hydrocarbons through flash pyrolysis catalyzed by an environmentally friendly MFI-type zeolite synthesized from rice husk ash and diatomite residue. A micro-pyrolyzer interfaced with chromatographic separation and mass spectrometry detection was used to compare the composition of condensable volatile products from catalytic pyrolysis over HZSM-5 with those from catalyst-free pyrolysis. Cassava peel, characterized by high volatile matter content (84.3 %), low ash content (3.19 %), and reasonable energy content (15 MJ kg −1), yielded a high content of valuable platform chemicals, such as carboxylic acids and furans, when subjected to catalyst-free pyrolysis. The catalytic upgrading pyrolysis vapors over the environmentally friendly HZSM-5 catalyst yielded approximately 56.0 % industrially relevant aromatic hydrocarbons and 39.9 % light organic acids. Other strengths of using HZSM-5 in upgrading pyrolysis vapors were its low selectivity for naphthalenes, precursors for coke formation, and the production of hydrocarbons in the gasoline range. Thus, HZSM-5 was an efficient catalyst for promoting deoxygenation and improving hydrocarbon content, with high selectivity for valuable aromatic hydrocarbons. In conclusion, cassava peel showed favorable prospects for conversion into hydrocarbon-rich bio-oil, serving as a valuable precursor for low-carbon biofuels.

MFI-Type Zeolite Nanosheets with Controllable Length along the b-Axis for Methanol-to-Propylene Reactions

MFI-Type Zeolite Nanosheets with Controllable Length along the <i>b</i>-Axis for Methanol-to-Propylene Reactions

Synthesis of iron-loaded MFI-type (Fe/ZSM-5) zeolite using Philippine natural zeolites (PNZ) for potential adsorption and catalytic applications

Abstract Philippine natural zeolites (PNZ) are locally abundant aluminosilicates used in different applications such as filtration and purification. However, the presence of impurities limits their usability. Structure modification of PNZ into a new framework was conducted in the study to address this issue. This study used PNZ as a precursor in the sustainable synthesis of iron-loaded MFI-type (Fe/ZSM-5) zeolite, a synthetic zeolite extensively studied for its excellent catalytic activity and high adsorption capacity. PNZ was depolymerized into active silica and alumina, then recrystallized via hydrothermal synthesis. Ammonium iron citrate (AIC) and TPAOH were used as the iron source and structure-directing agent, respectively. The disappearance and appearance of FTIR peaks in the depolymerized PNZ spectra deduced the successful destruction of the initial zeolite framework of the PNZ. The synthesized material was characterized using FTIR, XRD, SEM-EDS, TGA, and BET analyses. FTIR showed the crystallinity peak of MFI-type zeolite, while XRD confirmed its successful synthesis. SEM images show hierarchical aggregated particles suggesting the presence of intercrystalline and intracrystalline mesopores. The BET surface area of the synthesized zeolite increased by 168% compared to the raw PNZ, and TGA results show its high thermal stability. EDS analysis confirmed the presence of iron in the sample.

Sn-MFI zeolite nanosponge having high content of Lewis acid sites on external surfaces, exhibiting high activity in Baeyer-Villiger oxidation of bulky ketone

We developed a three-step synthesis strategy to obtain Sn-incorporated MFI-type zeolite nanosponge (Sn-MFI-ns) assembled by ultrathin (∼2.5 nm) zeolite frameworks possessing uniform-sized (∼4 nm) mesopores: 1) synthesis of MFI-type borosilicate nanosponge using a zeolite structure-directing-surfactant, 2) deboronation of the borosilicate using HNO3, and 3) gas-phase incorporation of Sn into the boron-vacant sites via silanol groups using (CH3)2SnCl2 as a precursor. The Sn-MFI-ns shows high crystallinity, consequently high thermal stability, and highly porous structure. The Sn content can be systematically controlled by the amount of the precursor, with Si/Sn ratios ranging from 30 to 200. The Sn species is highly dispersed over entire range of the zeolite surfaces, acting as Lewis acid sites. Due to the highly mesoporous structure, the Sn-MFI-ns has a significant number of Lewis acid sites on the external surfaces and mesopore walls, which are easily accessible to bulky molecules, compared to solely microporous zeolite (Sn-bulk-MFI). Consequently, the Sn-MFI-ns exhibits much higher catalytic activity than the Sn-bulk-MFI with high product selectivity in Baeyer-Villiger oxidation of 2-adamantanone, a molecule larger than the micropore apertures of MFI-type zeolite. The activity of Sn-MFI-ns is comparable to Sn-MCM-41 exposing almost all Sn to mesopore walls, advantageous to the bulky molecules’ reaction.

STUDY OF THE COMBINED EFFECT OF POST-SYNTHETIC ALKALINE TREATMENT AND NICKEL MODIFICATION OF MFI ZEOLITE ON THE DYNAMICS OF ITS DEACTIVATION IN THE PROCESS OF REFINING STRAIGHT-RUN GASOLINE

To determine the combined effect of post-synthetic treatments on the catalytic properties of MFI type zeolite (other names ZSM-5 or pentasil) during the upgrading of straight-run gasoline fraction of oil, MFI zeolite was synthesized and on its basis a sample was obtained, treated with an alkaline solution, as well as a nickel-containing sample after alkaline treatment of the zeolite. Modification of zeolite powder treated with an alkaline solution with nanosized nickel powder was carried out by dry mechanical mixing of the original powders in a vibrating mill. The activity and dynamics of deactivation of the obtained zeolite catalysts during the upgrading of straight-run gasoline fraction of oil were studied. Along with determining the characteristics of the target reaction products - high-octane gasoline, an analysis of the resulting gaseous hydrocarbons was carried out and the amount of carbon compaction products was determined. It has been shown that post-synthetic treatments of zeolite have a positive effect on the qualitative composition and yield of catalysates and reduce the rate of deactivation of zeolite catalysts. Post-synthetic alkaline treatment of MFI zeolite significantly reduces its aromatizing and cracking activity, resulting in an increased yield of high-octane gasoline with improved environmental characteristics. The introduction of nickel nanopowder into alkali-treated zeolite further enhances this tendency. Carrying out post-synthetic treatments of zeolite increases the time of stable operation of the resulting zeolite systems in the process of upgrading straight-run gasoline and reduces the amount of carbon compaction products formed. The state, location and dimensions of the zeolite carrier, nickel particles and carbon compaction products were determined using the transmission electron microscopy method. It has been shown that oxidative regeneration of a carbonized catalyst makes it possible to almost completely remove the resulting carbon deposits from the surface of both the active component and the zeolite support. For citation: Velichkina L.M., Gerasimov E.Yu., Vosmerikov A.V. Study of the combined effect of post-synthetic alkaline treatment and nickel modification of MFI zeolite on the dynamics of its deactivation in the process of refining straight-run gasoline. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 8. P. 103-112. DOI: 10.6060/ivkkt.20246708.10t.

Reinforcement and reconfiguration of framework Al in P@ZSM-5 zeolite via in-situ phosphating strategy for efficient methanol-to-propylene

In this work, a "bottom-up" strategy was proposed to one-step, in-situ synthesize P@ZSM-5 zeolites in a sodium-free system by elaborately self-designed tetrapropylphosphonium hydroxide as a new member of MFI-type zeolite organic templates inventory, and the interaction of phosphorus species with framework aluminum was investigated in detail. Multiple advanced characterizations confirm that the tetrahedrally-coordinated bidentate PIV-O2-AlIV structures are precisely customized and uniformly scattered in the zeolite channels. After experiencing harsh hydrothermal treatment (100 %H2O, 800 °C, 17 h), this new structure endows excellent hydrothermal stability of zeolite (crystallinity retention beyond 95 %) and reinforces its Brønsted acidity. Furthermore, methanol-to-propylene tests show that directly synthetic P@ZSM-5 zeolite performs extraordinarily long lifetime (180 h, WHSV = 1 h−1), enviable propylene selectivity (60.4 %) and propylene/ethylene ratio (ca. 4.3) compared to the counterparts, which is benefited from encouragingly olefinic cycle pathway. These findings afford value-filled opportunities in novel catalyst production mode and understandings for phosphorus-zeolite chemistry. Synopsis-A "bottom-up" strategy was demonstrated to one-step, in-situ synthesize P@ZSM-5 zeolite in a sodium-free system by elaborately self-designed tetrapropylphosphonium hydroxide. The resultant P@ZSM-5 catalyst with hyperuniformly-stable bidentate PIV-O2-AlIV structures exhibited extraordinarily long lifetime (180 h) and enviable propylene selectivity (60.4 %).

Investigating the Physical and Operational Characteristics of Manufacturing Processes for MFI-Type Zeolite Membranes for Ethanol/Water Separation via Principal Component Analysis

In this study, Principal Component Analysis (PCA) was applied to discern the underlying trends for 31 distinct MFI (Mobil No. 5)-zeolite membranes of 11 textural, chemical, and operational factors related to manufacturing processes. Initially, a comprehensive PCA approach was employed for the entire dataset, revealing a moderate influence of the first two principal components (PCs), which collectively accounted for around 38% of the variance. Membrane samples exhibited close proximity, which prevented the formation of any clusters. To address this limitation, a subset acquisition strategy was followed, based on the findings of the PCA for the entire dataset. This resulted in an enhanced overall contribution and the revelation of diverse patterns among the membranes and the considered manufacturing factors (total variance between 55% and 77%). The segmentation of the data unveiled a robust correlation between silica (SiO2) concentration and pervaporation conditions. Additionally, a notable clustering of the chemical compositions of the preparation solutions underscored their significant influence on the operational efficacy of MFI zeolite membranes. On the other hand, an exclusive chemical composition of the preparation solution was noticed. This highlighted the high influence of the chemical composition on the operational efficiency of MFI zeolite membranes. The coupling of PCA with experimental results can provide a data-driven enhancement strategy for the manufacturing of MFI-type zeolite membranes used for ethanol/water separation.

Efficient degradation of naproxen in wastewater using Ag-deposited ZnO nanoparticles anchored on a house-of-cards-like MFI-type zeolite: Preparation and physicochemical evaluations of the photocatalyst

We utilized Pr6-diquat-5 as an organic structure-directing agent (OSDA) to synthesize hierarchically intergrown ZSM-5 (HI-ZSM-5) as a catalytic support. ZnO particles were deposited onto HI-ZSM-5 via precipitation to remediate naproxen (NPX) in wastewater, while Ag was photo-deposited onto ZnO to prevent electron-hole pair recombination. XRD analysis revealed crystalline structures and particle sizes influenced by synthesis temperatures, and FT-IR confirmed ZnO and Ag deposition onto HI-ZSM-5 surfaces. Based on N2 adsorption-desorption isotherms, all samples exhibited Type I and IV isotherms with H4-type hysteresis loops, indicating the presence of both micro- and mesopores within HI-ZSM-5. XPS analysis confirmed the presence of peaks indicating Zn in ZnO and metallic Ag interacting with ZnO. TEM analysis identified aggregated Ag/ZnO nanoparticles in the photocatalysts, while EDX confirmed uniform element distribution. FE-SEM images revealed a uniform distribution of ZnO and Ag on HI-ZSM-5 with “house-of-cards” morphologies. PL analysis indicated reduced electron-hole recombination and an extended lifespan. NPX photodegradation experimental results showed that the reaction rate constant of the 3 %AZ composite was 2.8 times higher than that of ZnO/HI-ZSM-5 (0.0163 vs. 0.059 min−1, respectively). Evaluation of influential operating parameters demonstrated 90.8 % elimination of NPX under optimum conditions: a catalyst dosage of 1.5 g L−1 at pH 5 within 120 min. The impact of common anions on NPX decontamination and the catalyst's capability for COD and TOC removal (up to 62.6 and 53.4 %, respectively) was also discussed. The 3 %AZ optimum catalyst could be recycled for 5 cycles with remarkable reusability, maintaining 80.1 % removal efficiency after five regeneration cycles.

Dynamics-driven tailoring of Zr-embedded hierarchical ZSM-5 zeolites for enhanced catalytic performance from furfural to alkyl levulinate

The tandem reaction for generation of alkyl levulinate (AL) from bio-derived furfural (FUR) is environmental-friendly, in which the bifunctional catalyst with both metal active sites and acid sites are required. In this contribution, a MFI-type nanosponge zeolite with Zr-Al co-framework (Zr@NPZ) were one-pot hydrothermally synthesized using dual-template method. Series characterizations demonstrate that, highly dispersed Zr species embeds in the hierarchical zeolite framework and exhibits typical Lewis acids. Using isopropanol as solvent, Zr@NPZ catalyst gives isopropyl levulinate (IPL) yield up to 75.5 wt% at 180 °C after 2 h reaction from FUR, through sequenced transfer hydrogenation and hydrolysis, with production rates of 11.5 mmol g−1h−1. Moreover, although the enhanced acidities accelerate the conversion rates of FUR, the generation of β-angelica lactone (AGL) from 2-(isopropoxymethyl)furan (IPMF) and conversion of IPL to γ-valerolactone (GVL) are promoted, sacrificing the yield of IPL in the product. The synergism between high dispersed Zr species and moderate acid distribution lead to relative high yield of target IPL.

Boosting propane dehydrogenation performance over the highly dispersed Co(Ⅱ) sites on ultra-high silica ZSM-5 zeolite

Propane dehydrogenation (PDH) has emerged as an effective way to address the problem of propylene production gap in recent years. However, industrial catalysts are challenged by the scarcity of Pt and toxicity of CrOx. Herein, a series of Co-based catalysts supported on MFI type zeolites with various Si/Al ratios were synthesized by regulating the acid sites to alleviate side reactions. The catalyst Co/ZSM-5-1500 exhibits the superior PDH performance due to the highest proportion of Co(Ⅱ) active sites. The initial C3H6 formation rate is 6.5 mmol g−1cat h−1, along with good long-term stability across three cycles. The Brønsted acid sites over ZSM-5-40 are prone to catalyzing side reactions of cracking and coke deposition to decrease propylene selectivity and stability. This work demonstrates that Co species supported on high silica ZSM-5 zeolite via impregnation method is favorable to generate the highly dispersed Co(Ⅱ) species on the surface of zeolites, and the Co(Ⅱ) species are responsible for excellent PDH performance.

Revealing the effect of framework acidity on the catalytic combustion of vinyl chloride over zeolite-based catalysts

The study explored the effect of different types of acid sites on the catalytic combustion of vinyl chloride over zeolite-based catalysts. MFI-type zeolites were synthesized using impregnation method and loaded with the noble metal Ru. Results indicated that the Ru/Sn-MFI catalysts possessed only Lewis acid sites, the Ru/Al-MFI catalysts were primarily governed by Brønsted acid sites, and the Ru/Si-MFI catalysts had no acid sites. The Ru/Sn-MFI catalyst containing Lewis acid sites demonstrated increased catalytic activity, with a T90 of up to 306 °C, and efficiently prevented the formation of chlorinated by-products. In contrast, the Ru-Si/MFI catalyst exhibited inferior catalytic activity. While a significant amount of chlorinated by-products was generated on the Ru/Al-MFI catalyst. The substantial amount of Lewis acid sites on the surface of Ru/Sn-MFI catalyst facilitated the activation of C-Cl bonds and the cleavage of C–C bonds. Furthermore, the Ru/Sn-MFI catalysts had improved low-temperature reducibility and oxygen mobility, which contributed to the deep oxidation of vinyl chloride.

Enhanced azeotropic C2ClF5/C3F8 separation by TMA+ exchanged MFI zeolites for ultrapure fluorine electronic gas

AbstractThe demand for the azeotropic C2ClF5/C3F8 separation continues to rise owing to the significance of ultrapure fluoride gases for the electronic industry. With a boiling point differential of 1.1 K, separating an azeotropic mixture of C2ClF5/C3F8 through sorption‐based processes under ambient conditions is a preferable alternative to the current energy‐intensive cryogenic separation method. Here, we report the highly efficient C2ClF5/C3F8 adsorption separation in quaternary alkylammonium ions modified MFI type zeolites with interlaced channels which provide a cooperative effect conferred by specific interaction sites and optimal pore size. A path‐regulatory mechanism was proposed, whereby TMA+ cations located at intersections resembling “train turnouts” force gas molecules to switch traffic channels to confined sinusoidal channels affecting the C2ClF5/C3F8 recognition sites and diffusion behavior. Molecular simulations were conducted to reveal the separation mechanism, and the breakthrough experiment validated the effectiveness of this adsorbent at 298 K outperforming conventional adsorbents for the challenging azeotropic separation.

Wulff Constructions for an Equilibrium MFI-Type Zeolite Shape Modelling under Different Conditions

As an MFI-type zeolite, ZSM-5 zeolite has wide applications in industry, such as in the fine chemical, petrochemical, and coal chemical industries. However, shape control of ZSM-5 nanocrystals constitutes one of the major challenges of current nanotechnology. Here, the MFI framework structure was used as the theoretical model of pure silicon ZSM-5 to investigate the surface energy and Wulff shape. The models with different crystal surfaces were simulated by molecular dynamics (MD) with the assistance of machine learning potentials (MLPs). The factors influencing the crystal surface energy, such as temperature, pH, and ionic concentration, have been studied in detail. Depending on the calculated surface energies, the crystal surface morphology and its ratio were obtained by means of the Wulff theorem. The results show that the area in the equilibrium shape of the (110) surface is usually the largest, and its proportion varies with external conditions. A high temperature and high concentration of the aluminum source promoted the growth of the (110) crystal surface, and the theoretical value of the crystal surface ratio was as high as 90%. This study provides theoretical insight into the synthesis of zeolites with different morphologies of all-silicon or low-aluminum.

Tailoring the acidity of ZSM-5 via surface passivation: Catalytic assessment on dimethyl ether to olefins (DTO) process

In the present study, four different samples having different acidity were synthesized. Two MFI-type zeolites having silicon-to-aluminum ratio equal to 25 and 50 were prepared. Besides, two additional samples were obtained by external passivation of each parent zeolite with a layer of Silicalite-1, leading to a core–shell structure. Each sample was characterized to assess textural properties, structure, composition, and acidity, and then tested for dimethyl ether (DME) conversion at different reaction temperatures between 300 and 375 °C. The analysis of produced mixture revealed the simultaneous presence of hydrocarbons and methanol. DME conversion grew by increasing the temperature. Propylene was the most abundant hydrocarbon detected during all the time-on-stream analyses. Especially at 375 °C, the investigated samples having greater acidity showed faster deactivation due to coking. Samples with lower acidity were thus more stable but, on the other hand, they presented higher methanol selectivity and lower hydrocarbons yield.

Influence of temperatures and loadings on olefin diffusion in MFI-type zeolites in one- to three-dimensions

A detailed understanding of the molecular diffusion in zeolite frameworks is crucial for analysing the factors controlling their catalytic performance in alkenes.

Investigating synergistic cooperativity of metal-Brønsted acid site pair in MFI-type zeolites by synchrotron X-ray powder diffraction

This study examines how the modulation of the metal-BAS pair in MFI zeolite affects the catalytic performance in two catalytic reactions. The impact of acid strengths on catalytic properties is analyzed using Rietveld refinement and DFT calculations.

Exploring the effect of Brønsted acidity of MFI-type zeolites on catalytic cracking temperature of low density polyethylene

We verified the effects of the zeolite Brønsted acidity (acid strength, acid amount, location of acid sites, etc.) on the catalytic cracking temperature of low density polyethylene.

A nickel silicate MFI-type zeolite catalyst prepared by interzeolite transformation: tailoring the catalytic active sites for glucose conversion

A nickel silicate MFI-type zeolite catalyst prepared by interzeolite transformation: tailoring the catalytic active sites for glucose conversion

Influence of sulfur contamination on ethylene aromatization over a Ga-modified MFI-type zeolite

To develop a new CO2 utilization process from sulfur-containing gases, such as sour gas and biogas, we investigated the influence of trace amounts of sulfur gas, namely hydrogen sulfide and methanethiol (CH3SH), on ethylene aromatization over an MFI-type zeolite catalyst. The protonated MFI-type zeolite showed high activity and stability for ethylene aromatization; however, its activity rapidly deteriorated in the presence of trace amounts of CH3SH. To improve the catalytic activity, zeolite was modified with Ni, Cu, Zn, and Ga. Although modifications with Ni, Cu and Zn did not improve the catalytic activity for ethylene aromatization, Ga modification contributed to the stability of ethylene aromatization in the presence of trace amounts of CH3SH. Characterization of the as-made catalysts indicated that Ga modification not only weakened the surface acidity of the zeolite but also endowed the catalyst with dehydrogenation capability. These properties suppressed CH3SH decomposition on the acid site, leading to stable catalytic performance for ethylene aromatization in the presence of trace amounts of sulfur gas.