ZSM-5 Zeolite Research Articles

K+ promoted fabrication of nanoneedle low-silicon ZSM-48 mesocrystal

Owing to their distinct structural properties, low-dimensional zeolites are rising stars in the field of catalysis. However, shortening their size while maintaining the acidity continues to be challenging. In addition, simplified synthesis methods to efficiently prepare low-dimensional zeolites with more skeleton types and extended frame components are also of great interest. Herein, a facile strategy is developed for fabricating ultrathin nanoneedle (ca. 6-8 nm in diameter of each needle) ZSM-48 mesocrystals with a low Si/Al ratio (ca. 27, close to the lowest synthesized so far). This is achieved by adding potassium ions in a ZSM-12 synthetic system. The promoting effect of appropriate K+ ions was confirmed by adjusting the gel composition and tracking the crystallization process. Moreover, a superior conversion, reusability and regeneration performance for xylose to furfural is achieved with more accessible acidity and a more suitable Lewis/Brønsted acid ratio, which further expands the development of ZSM-48 zeolite.

Enhancing the catalytic performance of H-ZSM-5 in bio n-butanol dehydration by zeolite crystal engineering

NH4F etching is used as an unbiased chemical etching technique to hierarchize commercially available nano-sized ZSM-5 crystals. A structure-function relationship is reported, describing how the introduction of mesoporosity in a microporous ZSM-5 zeolite significantly increases its catalytic performance in (aqueous) n-butanol dehydration. Three parent samples are etched under two severity modes: mild (5 minutes of etching) and harsh (40 minutes of etching). Intrinsic features of the parent ZSM-5’s, such as their silanol populations, influence the outcome of the etching procedure. For all materials, crystallinity is unaffected, total pore volume increases while micropore volume is almost constant, and active site accessibility increases. For all materials, etching increases the catalytic activity for n-butanol dehydration. Cofeeding water to n-butanol further increases the stability of all catalysts. Microkinetic modeling reveals that the increased activity is related to a decreased stability of dibutyl ether (DBE), the most abundant surface intermediate. A decreased DBE adsorption energy, due to the increased accessibility of the acid sites, facilitates its desorption. NH4F etching, a flexible and easy technique to engineer zeolites' textural properties, does not affect the intrinsic nature and quantity of their active sites, leading to superior catalytic performances. Our results highlight the possibility to further increase the efficiency of zeolite catalysis in biomass conversion processes.

Effect analysis on the hydrocarbon adsorption performance enhancement of the different zeolite molecular sieves in the gasoline engine under the cold start process

In this work, the adsorption performance of ZSM-5, Beta-A, and NON zeolites on hydrocarbons emitted from the engine is investigated for selecting the best suited zeolite molecular sieves for hydrocarbon traps during the cold-start phase of the engine. Based on the giant canonical Monte Carlo (MC) method for adsorption simulation, the single-component, multi-component maximum adsorption, adsorption isotherms, adsorption sites of different hydrocarbon molecules on ZSM-5, Beta-A, and NON molecular sieves were investigated by using C2H2, C2H4, C3H6, and C7H8 molecules as probe molecules. The single-component adsorption results showed that for the macromolecular hydrocarbon toluene (C7H8) Beta-A zeolite had the best adsorption effect, followed by ZSM-5 zeolite, and NON had the worst adsorption effect. The adsorption of propylene (C3H6) on ZSM-5 and Beta-A is close to each other, and the adsorption of ethylene (C2H4) and acetylene (C2H2) are much different relative to C3H6 and C7H8. This is due to the fact that the adsorption properties of zeolites are determined by the molecular diameter of the hydrocarbons. The results of multicomponent adsorption showed that the adsorption amounts of multicomponent competitive adsorption were reduced relative to single-component adsorption, but were affected by other components in different ways, from small to large C7H8<C3H6<C2H4<C2H2.

PEPICO analysis of catalytic reactor effluents towards quantitative isomer discrimination: DME conversion over a ZSM-5 zeolite.

The methanol-to-hydrocarbons (MTH) process involves the conversion of methanol, a C1 feedstock that can be produced from green sources, into hydrocarbons using shape-selective microporous acidic catalysts - zeolite and zeotypes. This reaction yields a complex mixture of species, some of which are highly reactive and/or present in several isomeric forms, posing significant challenges for effluent analysis. Conventional gas-phase chromatography (GC) is typically employed for the analysis of reaction products in laboratory flow reactors. However, GC is not suitable for the detection of highly reactive intermediates such as ketene or formaldehyde and is not suitable for kinetic studies under well defined low pressure conditions. Photoelectron-photoion coincidence (PEPICO) spectroscopy has emerged as a powerful analytical tool for unraveling complex compositions of catalytic effluents, but its availability is limited to a handful of facilities worldwide. Herein, PEPICO analysis of catalytic reactor effluents has been implemented at the FinEstBeAMS beamline of MAX IV Laboratory. The conversion of dimethyl ether (DME) on a zeolite catalyst (ZSM-5-MFI27) is used as a prototypical model reaction producing a wide distribution of hydrocarbon products. Since in zeolites methanol is quickly equilibrated with DME, this reaction can be used to probe vast sub-networks of the full MTH process, while eliminating or at least slowing down methanol-induced secondary reactions and catalyst deactivation. Quantitative discrimination of xylene isomers in the effluent stream is achieved by deconvoluting the coincidence photoelectron spectra.

Ternary system with sandwich configuration facilitates aromatic production from CO2 hydrogenation

Enhancing the selectivity of light olefin intermediates is crucial for efficiently synthesizing aromatic hydrocarbons from CO2 hydrogenation. However, due to the limitations of Anderson-Schulz-Flory law, the oriented synthesis of light olefins over Fe-based catalysts is challenging. Herein, we creatively insert Y zeolite between the Fe-based catalyst and ZSM-5 zeolite to form a sandwich configuration. The excellent cracking function of sandwich Y zeolite enables the products before the aromatization to be concentrated in the light unsaturated hydrocarbons, leading to a high aromatic selectivity during the succedent aromatization processes. With the assistance of Y zeolite, the light olefin selectivity of the K-Fe catalyst increases from 30.8 % to 40.3 %. After combining with ZSM-5 zeolite, the aromatic selectivity of the ternary system is boosted from 27.6 % to 51.5 % compared to the bifunctional catalysts without Y zeolite. Our studies offer insightful guidance for the rational utilization of multifunctional zeolites to directly synthesize target products.

In Situ Growth of Mn-Co3O4 on Mesoporous ZSM-5 Zeolite for Boosting Lean Methane Catalytic Oxidation

The low-temperature oxidation of methane gas in coal mine exhaust gas is important for reducing the greenhouse effect and protecting the environment. Unfortunately, the carbon–hydrogen bonds in methane molecules are highly stable, requiring higher reaction temperatures to achieve effective catalytic oxidation. However, metal oxide-based catalysts face the problem of easy sintering and the deactivation of active components at high temperatures, which is an important challenge that catalysts need to overcome in practical applications. In this work, a series of Mn-Co3O4 active components were grown in situ on ZSM-5 zeolite with mesoporous pore structures treated with an alkaline solution via a hydrothermal synthesis method. Due to the presence of polyethylene glycol as a structure-directing agent, manganese can be uniformly doped into the Co3O4 lattice. The large specific surface area of ZSM-5 zeolite allows the active component Mn-Co3O4 to be uniformly dispersed, effectively preventing the sintering and growth of active component particles during the catalytic reaction process. It is worth mentioning that the Mn-Co3O4/meso-ZSM-5-6.67 catalyst has a methane conversion rate of up to 90% at a space velocity of 36,000 mL·g−1·h−1 and a reaction temperature of 363 °C. This is mainly due to the mesoporous ZSM-5 carrier with a high specific surface area, which is conducive to the adsorption and mass transfer of reaction molecules. The active component has an abundance of oxygen vacancies, which is conducive to the activation of reaction molecules and enhances its catalytic activity, which is even higher than that of noble metal-based catalysts. The new ideas for the preparation of metal oxide-based low-temperature methane oxidation catalysts proposed in this work are expected to provide new solutions for low-temperature methane oxidation reactions and promote technological progress in related fields.

Production of isopropyl levulinate from furfural catalyzed by zirconium phosphate supported on nanosponge MFI zeolite through catalytic transfer hydrogenation

Alkyl levulinate is a kind of high value chemicals derived from biomass. Here, a nanosponge ZSM-5 supporting zirconium phosphate (ZrPO/NPZ) catalyst is prepared and used for catalytic transfer hydrogenation of furfural (FUR) to produce isopropyl levulinate (IPL) using isopropanol as H-donor. ZrPO specie provides Lewis acid sites together with additional Brønsted acid sites by ZSM-5 zeolite. Using the hierarchical ZSM-5 with exposed surface area as support, the dispersion of ZrPO active species increases, which facilitates the adsorption and conversion of FUR with the generation of 2-(isopropoxymethyl)furan (IPMF). The moderate Brønsted acid sites by zeolite promote the adsorption and activation of isopropanol, thus increasing the conversion rates of intermediate IPMF with formation of IPL. Furthermore, improved proportions of Brønsted/Lewis was detected with the increase of P/Zr ratios in the prepared catalysts, which is adverse for conversion of FUR. The optimized ZrPO/NPZ catalyst with P/Zr of 1 gives the best catalytic performance with IPL yield of ∼69 wt% after 3 h reaction at 200 °C (TOF of 6.98 mmol g−1 h−1), which provides an essential catalyst to produce IPL from FUR.

Hierarchized ZSM-5 Zeolite Synthesis using N-Methyldiethanolamine as a Novel Desilicate Agent: Impact on Methanol Adsorption and Resistance Improvement to Coke Poisoning

Hierarchized ZSM-5 Zeolite Synthesis using N-Methyldiethanolamine as a Novel Desilicate Agent: Impact on Methanol Adsorption and Resistance Improvement to Coke Poisoning

Constructing immobilized H3PO4 network in nanosized ZSM-5 zeolitic framework achieves high proton conductivity after acceleration acid leaching test

In the midst of demand for the high and stable anhydrous proton conducting membrane for the high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), phosphoric acid (PA)-doped polybenzimidazole (PBI) is positioned as one of the most promising candidates. The key to develop the PA-PBI is to address the issue of phosphoric acid leaching, which causes significant performance deterioration. Here we introduced the nanosized ZSM-5 zeolite which plays the role of the rigid cage for confining H3PO4 to the PBI, and then evaluated by utilizing the acceleration acid leaching test (ALT) to put long-term operation in perspective. The ZSM-5 not only retain the high degree of PA after ALT, but also constructs the efficient proton conducting channel derived by the chemically-immobilized H3PO4 in pore channel. After ALT, PBI electrolyte membrane with 5 wt% of ZSM-5 exhibited 2.8 × 10−5 S cm−1 of proton conductivity at 150 °C anhydrous condition, which is three orders higher magnitude than pure PBI (1.1 × 10−8 S cm−1). Furthermore, H2/O2 HT-PEMFC single-cell constructed with PBI/5%ZSM-5 displayed an excellent maximum power density of 387 mW cm−2 at 150 °C anhydrous conditions, even after the ALT. The results indicate the possible improvement of the long-term stability of the fuel cell by utilizing readily available ZSM-5.

The dynamic catalysis of Ga/ZSM-5 catalysts for propane-CO2 coupling conversion to aromatics and syngas

Alkane coupling with CO2 by metal-containing zeolites catalysis is found to be a promising way to produce aromatics and syngas in recent years, but the real active sites and the role of CO2 are still unclear owing to the quick evolution of the metallic active sites and the complex reaction processes including direct propane aromatization, CO2 hydrogenation, reverse water–gas shift reaction, and propane-CO2 coupling aromatization. Herein, Ga/ZSM-5 catalysts were constructed to study the dynamic evolution of the metallic active sites and the role of CO2 during the propane and CO2 coupling reaction. After optimizing the reaction conditions, a notable propane conversion rate of 97.9% and an impressive aromatics selectivity of 80.6% in hydrocarbons can be achieved at the conditions of 550 °C and CO2/C3H8 of 4. 13CO2 isotope experiments illustrate that C-atoms of CO2 can enter into CO (86.5%) and aromatics (10.8%) during the propane-CO2 coupling reaction process. In situ XANES and FTIR spectroscopies at 550 °C and H2/C3H8 atmosphere reveal that GaOx species can be gradually dispersed into [GaH2]+/[GaH]2+ on the Brønsted acid sites of ZSM-5 zeolite during H2 and/or C3H8 treatment, which are the real active sites for propane-CO2 coupling conversion. In situ CO2-FTIR experiments demonstrate that the [GaH2]+/[GaH]2+ species can react with CO2 and accelerate the propane and CO2 coupling process. This work not only presents a cost-effective avenue for CO2 utilization, but also contributes to the active site design for improved alkane and CO2 activation in coupling reaction system.

Adsorption of rare earth elements (Ce3+, La3+, and Nd3+) and recovery from phosphogypsum leachate using a novel ZSM-5 zeolite

ZSM-5 zeolite is a multifunctional material highly efficient for adsorbing ions. Our ZSM-5 was synthesized by employing a nucleating gel as a structure-directing agent, followed by homogenization and hydrothermal treatment. The as-prepared ZSM-5 was physicochemically characterized to assess its properties. Next, the as-prepared zeolite was employed as an adsorbent to remove rare earth elements, REEs from synthetic solutions and real phosphogypsum leachate under batch mode operation. As expected, the ZSM-5 adsorbent was discovered to be highly microporous with abundant surface functionalities, which could positively impact REE adsorption. The adsorption data indicated a high affinity between ZSM-5 and all three REEs with rapid kinetics and high adsorption capacities. The modeling study suggested that the adsorption kinetic data were well fitted by Avrami-fractional order, and Liu described the equilibrium data. The maximum adsorption capacity for Ce3+, La3+, and Nd3+ were 99.42 mg g−1, 96.43 mg g−1, 118.10 mg g−1, respectively. Further, the thermodynamic analysis revealed that the interaction between ZSM-5 and Ce3+, La3+, and Nd3+ was favorable, spontaneous, and endothermic. The efficiency of ZSM-5 adsorbent was also studied in recovering several REEs from leachate of phosphogypsum wastes, and the data results proved its potency to do so. The findings reported in this work support the idea that ZSM-5 can be successfully used as an adsorbent to recover REEs from synthetic and real samples.

Robust, high-performance Cu-impregnated ZSM-5 zeolites for hydrocarbon removal during the cold-start period: Quantitative elucidation of effects of H+ and Na+ ions on performance and stability

Cu-containing zeolites are suitable for active hydrocarbon (HC) traps. Crucially, physicochemical properties of the zeolite could be finely tuned by varying the ion contents, though such approach has not been used intensively for HC trapping. Therefore, in this study, we adjusted the ratio of Na+ to H+ ions in ZSM-5 zeolites from 1 to 0 and, subsequently, wet-impregnated these zeolites with Cu. A low Na/Al ratio (≤0.4) resulted in marked cold-start test (CST) performance for HC removal in the fresh state (HC removal efficiency of 60.2 %-69.5 %). However, a hydrothermally treated counterpart having an optimal Na+ content (Na/Al ratio of 0.4) could well preserve the original active Cu+ ions along with zeolite structure and, accordingly, show the best CST performance after hydrothermal treatment (HT) at 800 °C (HC removal efficiency of 24.4 % vs. 10.8 % for the conventional H+-form-based one). Furthermore, we investigated adsorption behavior of water and HCs at a deep level and, further, revealed a clear correlation between the HC adsorption ability and CST performance and the representative physicochemical properties (mainly related to Cu+ ions) at all Na+ contents. Additionally, tiny CuO particles on the outer surface of the Cu-impregnated ZSM-5 zeolites having Na/Al ratios of 0–0.4 showed good low-temperature HC oxidation ability (ca. 175–182 °C). Although this HC oxidation ability was reduced after HT, an optimal Na/Al of 0.4 led to preservation of the original ability (ca. 283 °C vs. 320 °C for pure large CuO particles). Finally, we demonstrated a synergistic relationship between Na+ and H+ ion contents (Na/Al ratio of 0.4) that favored the formation of the desired Cu species, thus achieving marked HC adsorption and oxidation after HT.

A ZSM-5 zeolite nanosheet with single-unit-cell thickness templated by bi-ammonium surfactants with large-diameter hydrophobic groups

Ultra-thin zeolite nanosheets have received widespread attention due to their superior catalytic performance compared to bulk zeolites. Here, we have designed a new structure-directing agent with a tert-butyl benzene group as the large-diameter hydrophobic end of a bi-ammonium surfactant molecule. Using this novel structure-directing agent, zeolite nanosheets with a thickness of ∼ 2.5 nm were synthesized, which exhibit better catalytic performance than bulky zeolites in the Friedel-Crafts alkylation reaction of trimethylbenzene and benzyl alcohol.

Understanding the Structural and Catalytic Properties of Al(IV)-2 Acidic Sites of ZSM-5.

It is crucial to identify the structures of active sites to understand how catalysts function and to use that understanding to develop better catalytic materials. ZSM-5 zeolites with dominant Al(IV)-2 sites have been developed in this work. 1H-27Al 2D HMQC and 2D 1H TQ(DQ)-SQ NMR experiments have been performed to investigate the structural properties of this acidic site. The Al(IV)-2 sites have Brønsted and Lewis acid characteristics. The catalytic performance of Al(IV)-2 sites has been tested by n-dodecane cracking reactions. The catalytic results show that the Brønsted acidic strength of the Al(IV)-2 sites is comparable to that of the Al(IV)-1 sites, but the Al(IV)-2 sites' Lewis acid characteristics provide extra catalytic activity. We have gained valuable insights into the characteristics of Al(IV)-2 acid sites within these materials.

Comparative analysis of parent and modified ZSM-5 zeolites: Insights from positron annihilation lifetime spectroscopy

Modified zeolite ZSM-5 samples were prepared by synthesis in the presence of the organics acting as mesoporogens: cationic surfactant, hexadecyltrimethylammonium bromide (CTAB) and cationic polymer, polydiallyldimethylammonium chloride (PDADMAC), as well as by alkali etching of the parent zeolite. Properties of modified zeolites were compared to the parent ZSM-5 zeolite. X-ray diffractograms demonstrate that the obtained modified zeolite ZSM-5 samples in all cases have preserved parent crystalline zeolite framework of the MFI-type. However, scanning electron micrographs of the same samples show morphology variations of the modified samples as compared to the starting zeolite. Thermogravimetric analyses show distinct weight loss curves of the samples. Differences have been also noted in the hydroxyl stretching range of the infrared spectra, and in the results of positron annihilation lifetime spectroscopy (PALS) measurements, which indicated dissimilarities by probing free volume in parent and modified zeolite ZSM-5 samples. In that way, PALS as scarcely used technique in zeolite studies, proved its applicability in structural investigation of this kind.

Influence of Granulated Hierarchical Zeolite ZSM-5 Physicochemical Properties on Its Catalytic Performance in Skraup Synthesis of Quinolines

Influence of Granulated Hierarchical Zeolite ZSM-5 Physicochemical Properties on Its Catalytic Performance in Skraup Synthesis of Quinolines

Biochar-mediated synthesis of ZSM-5 zeolite for the methanol-to-olefins reaction

The present study reports the successful synthesis of ZSM-5 zeolites with high external specific surface area by using biochar as a hard template. The physicochemical properties of the biochars (originated from grass, tea and lignin) were studied using XRD, SEM EDX, FTIR and other characterization techniques. The results showed that biochars obtained from different plants, due to the differences in morphology, particle size, composition and surface functional groups, led to significant effects on the morphology and acidity of the zeolite crystals. These ZSM-5 zeolites exhibited a significantly improved performance in the Methano-To-Olefins (MTO) reaction. Indeed, the catalyst lifetime of parent ZSM-5 started to decline after 6 h, whilst ZSM-5 modified by Grass-C only suffered a loss in conversion after 10 h on stream (at 400 °C, WHSV=8 h−1).

Selective Upcycling of Polyethylene over Ru/H-ZSM-5 Bifunctional Catalyst into High-Quality Liquid Fuel at Mild Conditions.

It has been known that plastics with undegradability and long half-times have caused serious environmental and ecological issues. Considering the devastating effects, the development of efficient plastic upcycling technologies with low energy consumption is absolutely imperative. Catalytic hydrogenolysis of single-use polyethylene over Ru-based catalysts to produce high-quality liquid fuel has been one of the current top priority strategies, but it is restricted by some tough challenges, such as the tendency towards methanation resulting from terminal C-C cleavage. Herein, we introduced Ru nanoparticles supported on hollow ZSM-5 zeolite (Ru/H-ZSM-5) for hydrocracking of high-density polyethylene (HDPE) under mild reaction conditions. The implication of experimental results is that the 1Ru/H-ZSM-5 (~1 wt % Ru) acted as an effective and reusable bifunctional catalyst providing higher conversion rate (82.53 %) and liquid fuel (C5-C21) yield (62.87 %). Detailed characterization demonstrated that the optimal performance in hydrocracking of PE could be attributed to the moderate acidity and appropriate positively charged Ru species resulting from the metal-zeolite interaction. This work proposes a promising catalyst for plastic upcycling and reveals its structure-performance relationship, which has guiding significance for catalyst design to improve the yield of high-value liquid fuels.

Impacts of ball-milling on ZSM-5 zeolite properties and its catalytic activity in the two-phase glycerol ketalization with acetone

A series of acidic ZSM-5 zeolites were mechanically ball-milled for different periods and further applied as catalysts in the liquid-phase glycerol ketalization with acetone. Structural and textural characterizations showed that the samples had considerable crystallinity and micropore volume loss due to amorphization. On the other hand, due to a comminution effect, the external surface area increased and particle size reduced. TPD and FTIR analyses with probe molecules with different sizes, such as ammonia, pyridine (Py), and 2,6-di-tert-butylpyridine (DTBPy) chemisorbed on the catalyst acid sites, aided in quantifying the various levels of accessibility of chemicals. The treated materials lost acidity due to amorphization or blockage of pores, but the milling enabled higher accessibility of bulkier chemicals to acid sites, as revealed by the chemisorption of Py and DTBPy. A crucial balance of acidity, accessibility, and hydrophobicity was tailored by milling time. The one-hour grounded zeolite had a glycerol conversion 35 % greater than the pristine sample and 67 % greater than the eight-hour milled sample. The results showed that ball milling is a tool to improve the catalytic activity of zeolites with bulky chemicals by fine-tuning the milling time.

Physicochemical and Catalytic Properties of Bifunctional Catalysts with Different Contents of Zeolite ZSM-22 in the Hydrodeoxygenation of Sunflower Oil

Physicochemical and Catalytic Properties of Bifunctional Catalysts with Different Contents of Zeolite ZSM-22 in the Hydrodeoxygenation of Sunflower Oil