Hierarchical Mesoporous Zeolite Research Articles

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

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

Control of Zeta Potential of Hierarchical Mesoporous Zeolite Y via Inorganic Surface Modification without Micropore Blockage and Phase Separation

Control of Zeta Potential of Hierarchical Mesoporous Zeolite Y via Inorganic Surface Modification without Micropore Blockage and Phase Separation

Process optimization of biodiesel production via esterification of oleic acid using sulfonated hierarchical mesoporous ZSM-5 as an efficient heterogeneous catalyst

The development of effective heterogeneous catalysts for the production of biodiesel from low-cost feedstocks containing large amounts of free fatty acids has lately become one of the foremost research issues in the energy research area. Herein, hierarchical mesoporous ZSM-5 zeolite containing sulfonic acid groups (SO3H-HM-ZSM-5-3) was prepared via the hard template approach, using soluble starch as a cheap and sustainable mesoporegen, and the subsequent sulfonation using chlorosulfonic acid as a sulfonating agent. The catalytic activity of the synthesized catalyst was evaluated in the esterification of oleic acid with methanol, and the principal process variables were optimized, adopting the response surface methodology. Results revealed that the catalyst amount and reaction temperature seemed to be the most influential variables governing the esterification process. A maximum oleic acid conversion of 100% was achieved under the optimum operating conditions of 18:1 methanol-to-oleic acid molar ratio and 5.2 wt% catalyst amount (based on the mass of oleic acid) at 88 °C, for 10 h. The performance of the developed SO3H-HM-ZSM-5-3 catalyst was comparable to or even outperformed some other reported acidic catalysts. Importantly, the performance of SO3H-HM-ZSM-5-3 for biodiesel production from waste cooking oil doped with 15% of oleic acid was additionally explored, and methyl ester yield as high as 92.45% was achieved through the simultaneous esterification of free fatty acids and the transesterification of triglycerides. Accordingly, SO3H-HM-ZSM-5-3 appears promising as an industrial catalyst for the one-step biodiesel production from low-grade feedstocks containing high levels of FFAs.

Synthesis of Cost-Effective Hierarchical MFI-Type Mesoporous Zeolite: Introducing Diatomite as Silica Source

Zeolite, as an intricate microporous material with redox sites, has been widely examined in many chemical industries. However, zeolite is not available everywhere, and it is expensive considering the price of raw materials from which it can be synthesized. In this study, ZSM-5 zeolite, as a local silica source with the high crystallinity, was synthesized, based on diatomite exploited from a mine in the north-west of Iran. The diatomite was employed as the only source of silica, and underwent hydrothermal transformation in a Teflon-lined autoclave operating at 170 °C without any alkaline post-treatment. The effects of the reaction pH and the reaction time on the properties of the synthesized MFI-type zeolite were monitored. The hydrothermal reaction time was optimized and hierarchical ZSM-5 hexagonal crystals were obtained. Furthermore, the effect of Si/Al ratio on the crystallinity of the resulting zeolite was investigated. The XRD, SEM, TEM, BET, FTIR, TPD, TGA, and DSC analyses were carried out to characterize the synthesized zeolites. The results confirmed the creation of MFI-type zeolites from diatomite applying hydrothermal process at an optimized pH and reaction time. In addition, the synthesized ZSM-5 zeolites exhibited a narrow pore size distribution resembling the mesoporous structure of standard ZSM-5 zeolites. Plenty of regularly arranged pores with diameters of 300–500 nm were observed inside the round circle-like sections of diatomite. For zeolites in which Si/Al ratio was higher (55 compared to 37), a relatively narrower pore size distribution similar to that of the standard ZSM-5 zeolite was detected. Comparably, the synthesized zeolites also contained stronger acid sites, rendering it as an excellent catalyst for the conversion of methanol to gasoline.

Correction to: Sequential Microwave-Assisted Dealumination and Hydrothermal Alkaline Treatments of Y Zeolite for Preparing Hierarchical Mesoporous Zeolite Catalysts

The original version of this article unfortunately contained an error. The authors would like to correct the error with this erratum.

Sequential Microwave-Assisted Dealumination and Hydrothermal Alkaline Treatments of Y Zeolite for Preparing Hierarchical Mesoporous Zeolite Catalysts

A novel post-synthetic method combining the microwave (MW)-assisted dealumination and hydrothermal (HT) alkaline treatment for obtaining mesoporous Y zeolite catalysts is presented. In the first-step MW-assisted dealumination of the pristine Y zeolite, both the mineral acid (i.e. hydrochloric acid, HCl) and organic carboxylic acids (e.g. oxalic and diethylenetriaminepentaacetic acid) were used (all at 0.16 M), and their effects on the physical and chemical properties of the resulting modified zeolites (after the identical HT alkaline treatment using 0.2 M sodium hydroxide solution) are studied in detail by comprehensive characterisation of the bulk silicon-to-aluminium (SAR) ratio, crystallinity and textural properties. The findings show that, in the developed sequential method, (i) HCl was only effective to achieve the hydrolysis of the zeolite, (ii) carboxylic acids with the function of chelation was very capable of extracting Al species and creating mesopores, and (iii) the mesopores formation is a function of the number of coordination sites in the carboxylic acid. The hierarchical feature of the mesopores in the modified zeolites (using carboxylic acids) was probed by the model reaction of aldol condensation of 1-heptanal with benzaldehyde for the selective formation of jasminaldehyde. The normalised selectivity to jasminaldehyde (with respect to the strong acidity) was proportionally related to the specific mesopores volume of the zeolites, revealing hierarchical porous networks in the relevant modified Y zeolites and indicating the effect of hierarchical mesopores in the zeolites on their catalytic performance.

Facile synthesis of hydrothermally stable mesoporous ZSM-5 zeolite from Al- SBA-16 via steam assisted crystallization

In this work, Al grafted SBA-16 (Al-SBA-16) is converted into a fully crystalline hierarchical mesoporous ZSM-5 zeolite with hydrothermal stability by steam assisted crystallization under controlled conditions. The secondary mesoporosity is due to reorganization and recrystallization events happening upon steaming the precursor. Two mesoporous aluminosilicates (Al-SBA-16s) are used as the precursors of zeolites. The precursors are obtained by post-synthetic Al grafting on the silica walls of SBA-16 with aluminium isopropoxide and sodium aluminate. Mesoporous ZSM-5 zeolites obtained from the Al-SBA-16 precursors and commercial ZSM-5 are characterized using XRD, XRF, FT-IR, TEM, N2 adsorption, 27Al and 29Si MAS NMR, and TPD of NH3. The results indicated the presence of intraparticle mesoporosity in the prepared mesoporous zeolites and they have comparable crystallinity with commercial ZSM-5. Catalytic activity of the synthesized mesoporous zeolites in benzylation of mesitylene is found to be comparatively more than commercial ZSM-5, which shows existence of micro/meso hierarchical structure in the mesoporous ZSM-5 zeolites. The aluminium sources, aluminium isopropoxide and sodium aluminate have a remarkable influence on the textural, acidity, and hydrothermal stability characteristics of the synthesized mesoporous ZSM-5 zeolites.

Hydrodeoxygenation and hydrocracking of microalgae biodiesel to produce jet biofuel over H3PW12O40-Ni/hierarchical mesoporous zeolite Y catalyst

To improve jet biofuel quality with increased iso-alkane content, a bi-functional catalyst with strong acidity was proposed to promote hydrodeoxygenation and hydrocracking of microalgae biodiesel through loading heteropoly acid H3PW12O40 (HPW) on Ni-based hierarchical mesoporous zeolite Y (meso-Y). It was found by quantum chemistry calculation that hydrodeoxygenation process of microalgae biodiesel was inclined to the decarboxylation pathway other than the decarbonylation pathway, because the total enthalpy of pentadecane and byproducts obtained through decarboxylation of methyl palmitate (C16:0) was lower by 187.7 kJ/mol than that through decarbonylation. The selectivities of hydrocracking products with odd carbons (2n − 1, n = 5, 6, 7, 8) were higher than those with even carbons (2n), because the covalent bonds hydrocracked to remove even carbons were 0.001–0.149% longer in bond length and 0.012–1.697% lower in bond order than those hydrocracked to remove odd carbons. The experimental results of hydrodeoxygenation and hydrocracking conversion of microalgae biodiesel into jet biofuel carried out in a fixed bed reaction system agreed well with the quantum chemistry calculation results. The BET surface area of 10% Ni/meso-Y catalyst loaded with 4% HPW decreased by 14.3% to 453.9 m2/g, but its strong acid density increased by 30.6% to 1.62 mmol/g. Accordingly, the selectivity of jet biofuel in liquid products converted from microalgae biodiesel at 255 °C and 2 MPa hydrogen increased to 63.1%, in which iso-alkane selectivity markedly increased to 20.5% and arene selectivity was reasonable at 11.1%.

Diffusion of aromatic hydrocarbons in hierarchical mesoporous H-ZSM-5 zeolite

Hierarchical mesoporous zeolites exhibit higher catalytic activities and longer lifetime compared to the traditional microporous zeolites due to improved diffusivity of substrate molecules and their enhanced access to the zeolite active sites. Understanding diffusion of biomass pyrolysis vapors and their upgraded products in such materials is fundamentally important during catalytic fast pyrolysis (CFP) of lignocellulosic biomass, since diffusion makes major contribution to determine shape selectivity and product distribution. However, diffusivities of biomass relevant species in hierarchical mesoporous zeolites are poorly characterized, primarily due to the limitations of the available experimental technology. In this work, molecular dynamics (MD) simulations are utilized to investigate the diffusivities of several selected coke precursor molecules, benzene, naphthalene, and anthracene, in hierarchical mesoporous H-ZSM-5 zeolite. The effects of temperature and size of mesopores on the diffusivity of the chosen model compounds are examined. The simulation results demonstrate that diffusion within the microspores as well as on the external surface of mesoporous H-ZSM-5 dominates only at low temperature. At pyrolysis relevant temperatures, mass transfer is essentially conducted via diffusion along the mesopores. Additionally, the results illustrate the heuristic diffusion model, such as the extensively used Knudsen diffusion, overestimates the diffusion of bulky molecules in the mesopores, thus making MD simulation a powerful and compulsory approach to explore diffusion in zeolites.

Fabrication of novel hierarchical ZSM-5 zeolite membranes with tunable mesopores for ultrafiltration

A series of novel hierarchical ZSM-5 zeolite membranes with tunable mesopore sizes have been prepared successfully by using amphiphilic organosilane 3-[(trimethoxysilyl) propyl]octyldimethyl-ammonium chloride (TPOAC) as the mesogenous template and part of the Si source. The effects of several synthesis parameters, such as the TPOAC/SiO2 ratio, synthesis temperature and crystallization time, on the microstructures and rejection performance of the hierarchical ZSM-5 zeolite membranes were systematically investigated. Multiple techniques, such as XRD, SEM, N2 adsorption techniques, TEM, IR, 13C MAS NMR and 29Si MAS NMR were employed for the characterizations. The filtration of dextran in water shows that the membranes have molecular weight cutoff (MWCO) ranging from 9500 to 943,000, corresponding to the molecular size in the range of 4.5–37nm. The sharp increase in the rejection of dextran with the increase of molecular weight indicated narrow pore size distribution of the membrane. These results show that the hierarchical mesoporous ZSM-5 zeolite membranes have a great potential for ultrafiltration with high performance.

Upgrading of Napier grass pyrolytic oil using microporous and hierarchical mesoporous zeolites: Products distribution, composition and reaction pathways

Reaction pathways in ex-situ catalytic upgrading of pyrolytic oil towards formation of specific products such as hydrocarbons are still not well established due to the presence of many different organic components in the raw pyrolytic oil. Currently, only a few studies are available in literature particularly with regards to application of hierarchical mesoporous zeolite in the refinement of sample pyrolytic oil. This study provides the first experimental investigation of ex-situ catalytic upgrading of pyrolytic oil derived from Napier grass using microporous and hierarchical mesoporous zeolites. Two hierarchical mesoporous zeolites were synthesized by desilication of microporous zeolite using 0.2 and 0.3 M solution of sodium hydroxide. Upgrading over microporous zeolite produced 16.0 wt% solid, 27.2 wt% organic phase and 23.9 wt% aqueous phase liquid while modified zeolites produced 21–42% less solid and 15–16% higher organic phase liquid. Higher degree of deoxygenation of pyrolytic oil was achieved with the modified zeolites. Analysis of organic phase collected after catalytic upgrading revealed high transformation of oxygenates into valuable products. Bulk zeolite produced cyclic olefins and polyaromatic hydrocarbons while mesoporous zeolites were selective toward cycloalkanes and alkylated monoaromatic production, with significant reduction in the production of polyaromatic hydrocarbon. Result of gas analysis showed that hierarchical mesoporous zeolite favored decarboxylation and decarbonylation reactions compared to the parent zeolite, which promoted dehydration reaction. Mesoporous zeolite produced with 0.3 M sodium hydroxide solution was found to be the best-performing catalyst and its reusability was tested over four consecutive cycles. This study demonstrated that pyrolytic oil derived from Napier grass can be transformed into high-grade oil over hierarchical mesoporous zeolite.

Insight into catalyst deactivation mechanism and suppression techniques in thermocatalytic deoxygenation of bio-oil over zeolites

AbstractThe economic viability of the thermocatalytic upgrade of biomass-derived oxygenates is facing the challenge of low-quality products. This is because of leaching of active species, coking, and concomitant catalyst deactivation. These cumulate into the loss of catalytic activity with time on stream (TOS), which causes low degree of deoxygenation. Thus, this article reviews recent advances aimed at alleviating these setbacks to make the process viable for industrial scale-up. To understand the concept of catalyst deactivation and to offer solutions, the review scrutinized the deactivation mechanism diligently. The review also analyzes deactivation-suppression techniques such as nanocrystal zeolite cracking, hydrogen spilt-over (HSO) species, and composite catalysts (hybrid, hierarchical mesoporous zeolite, modified zeolites, and catalytic cracking deposition of silane). Interestingly, these deactivation-suppression techniques enhance catalytic properties mostly by reducing the signal strength of strong acid sites and increasing hydrothermal stability. Further, the approaches improve catalytic activity, selectivity, and TOS stability because of the lower formation of coke precursors such as polynuclear aromatics. However, despite these many advances, the need for further investigations to achieve excellent catalytic activity for industrial scale-up persists.

Synthesis and application of hierarchical mesoporous HZSM-5 for biodiesel production from shea butter

Here, we report the upgrading of shea butter to biodiesel with hierarchical mesoporous ZSM-5 zeolites (HMZeol). Shea butter is a triglyceride (mainly oleic and steric acid) extracted from African shea tree nut. The catalysts synthesis was by desilication of conventional ZSM-5 with an aqueous solution of NaOH (0.3 and 0.4 M). XRF, XRD, NH3-TPD and N2 adsorption unveiled the effect of desilication of the parent zeolite. The study investigated the effect of NaOH concentration on matrix area, pore size, mesopore volume and Si/Al ratio. HMZeol showed superior activity on biodiesel yield when compared with the parent ZSM-5 zeolite. The catalytic material treated with 0.4 M NaOH (0.4HMZeol) gave 74% biodiesel yield at 5:1 methanol/oil molar ratio, 1 wt% catalyst, and 200 ᵒ C for 3 h reaction time while ZSM-5 gave 46.05% yield under the same reaction conditions. Further increase in the reaction time to 12 h for 0.4HMZeol, 0.3HMZeol and ZSM-5 gave 82.12, 79.21, and 72.13% biodiesel yield respectively. These results showed that hierarchical mesoporous HZSM-5 is a promising solid acid catalyst for biodiesel production via methanolysis.

Synthesis of hierarchical mesoporous zeolites based on MOR zeolite: application in the automobile tailpipe hydrocarbon trap

Hierarchical mesoporous zeolites with different levels of micro- and mesoporosity were prepared by dissolution and reassembling processes of MOR zeolite in the presence of mesoscale cationic surfactant cethyltrimethylammonium bromide. The obtained materials were characterized by X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy, Fourier transform infrared, Nitrogen (N2) adsorption/desorption, Temperature programmed desorption of NH3 (NH3-TPD) and Nuclear magnetic resonance techniques. Moreover, these hierarchical zeolites were tested as hydrocarbon traps using toluene as probe molecule and the temperature programmed desorption method. The results showed that the amount of microstructure and mesostructure in the composite was able to be favorably tuned by varying dissolution time at the first stage. The hierarchical materials displayed remarkably high desorption temperature in toluene-TPD, which is an expected performance of hydrocarbon trap in automobile tailpipes. The effect is due to the easier transport of bulky molecules provided by mesopores and increasing the number of available active sites via a fragmentation of the microporous framework. Therefore, the synthesized composite molecular sieve may be a novel catalyst for hydrocarbon trap in automobile tailpipes.

Potential of sustainable hierarchical zeolites in the valorization of α-pinene.

In the valorization of α-pinene, which is an important biomass intermediate derived from turpentine oil, hierarchical (mesoporous) zeolites represent a superior class of catalysts. Hierarchical USY, ZSM-5, and beta zeolites have been prepared, characterized, and catalytically evaluated, with the aim of combining the highest catalytic performance with the most sustainable synthetic protocol. These zeolites are prepared by alkaline treatment in aqueous solutions of NH4 OH, NaOH, diethylamine, and NaOH complemented with tetrapropylammonium bromide. The hierarchical USY zeolite is the most attractive catalyst of the tested series, and is able to combine an overall organic-free synthesis with an up to sixfold activity enhancement and comparable selectivity over the conventional USY zeolite. This superior performance relates to a threefold greater activity than that of the commercial standard, namely, H2 SO4 /TiO2 . Correlation of the obtained benefits to the amount of solid lost during the postsynthetic modifications highlights that the highest activity gains are obtained with minor leaching. Furthermore, a highly zeolitic character, as determined by bulk XRD, is beneficial, but not crucial, in the conversion of α-pinene. The alkaline treatments not only result in a higher overall activity, but also a more functional external surface area, attaining up to four times the pinene conversions per square nanometer. The efficiency of the hierarchical USY zeolite is concomitantly demonstrated in the conversion of limonene and turpentine oil, which emphasizes its industrial potential.

ChemInform Abstract: Synthesis of Hierarchical Mesoporous Mn—MFI Zeolite Nanoparticles: A Unique Architecture of Heterogeneous Catalyst for the Aerobic Oxidation of Thiols to Disulfides.

An efficient procedure for aerobic oxidation of thiols to disulfides catalyzed by new self-assembled hierarchical mesoporous Mn–MFI in the presence of air under solvent-free conditions as well as in aqueous medium is reported. The mesoporosity and Mn4+ loading, together with a highly crystalline microporous pore wall structure of the MFI framework were achieved through a newly designed hydrothermal process. This hydrothermal approach leads to hierarchical self-assembled mesoporous zeolite structures through isomorphous substitution of Si by Mn and Al. It is shown that Mn-containing mesoporous zeolites are capable to form disulfide bonds from thiols in the presence of air. The zeolitic materials were characterized by XRD, field-emission scanning electron microscopy, high-resolution TEM, X-ray photoelectron spectroscopy, 29Si NMR, 27Al NMR, and EPR spectroscopy, as well as AAS analysis and N2 sorption studies. N2 sorption analysis revealed high surface areas and narrow pore size distributions (1.2–6.0 nm) for different samples. The mesoporous Mn–ZSM-5 acted as an efficient heterogeneous catalyst with maximum catalytic activity in the benzenethiol conversion to diphenyldithiol.

Investigation on the morphology of hierarchical mesoporous ZSM-5 zeolite prepared by the CO2-in-water microemulsion method

A series of hierarchical mesoporous ZSM-5 zeolites with different morphology were successfully synthesized by the CO2-in-water microemulsion method, and mesoporosity was formed without organotemplate. The different synthesis conditions, including silica alumina molar ratio, stirring time and compressed CO2 pressure, were systematically investigated to discuss the influence of these conditions on the morphology of ZSM-5 zeolite. The resulting samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma (ICP) and nitrogen adsorption-desorption measurement. XRD results indicated that compressed CO2 route for the synthesis of MFI zeolites had a fast crystallization rate and good crystallinity. SEM images showed that the ZSM-5 hierarchical mesoporous ZSM-5 zeolite had a uniform chain-like crystal morphology, whereas silicalite-1 displayed a monodisperse crystal morphology. In addition, the nitrogen adsorption-desorption measurement provided sufficient evidence for the presence of hierarchical mesopores in ZSM-5 zeolite.

Hierarchical mesoporous ZSM-5 for the dehydration of methanol to dimethyl ether

Hierarchical mesoporous ZSM-5 zeolites were synthesized using small organic cations of tetrapropylammonium and meso-sized cationic polymers of dimethyldiallyl ammonium chloride acrylamide copolymer as templates. The zeolites were used for the dehydration of methanol to dimethyl ether (DME). Characterization results showed that the basic MFI-type structure was still obtained after adding the cationic polymers, while their nitrogen isotherms exhibited a broad hysteresis loop at relative pressures higher than 0.4, which proved the presence of mesopores. The mesoporosity of the hierarchical mesoporous ZSM-5 can be adjusted simply by adding different amounts of the cationic polymer. Catalytic tests showed that the hierarchical mesoporous HZSM-5 zeolites exhibited better stability than conventional HZSM-5 and excellent DME selectivity. The activity for methanol dehydration strongly depended on the textural property and acidity of the catalyst. The synthesized hierarchical mesoporous HZSM-5 zeolites exhibited better catalytic activity than conventional HZSM-5, indicating that hierarchical mesopores play an important role in the methanol to dimethyl ether process.

Hierarchical mesoporous ZSM-5 zeolite with increased external surface acid sites and high catalytic performance in o-xylene isomerization

Surface acid sites of hierarchical mesoporous ZSM-5 zeolite synthesized by steam-assisted crystallization were characterized by NH3 temperature-programmed desorption and in-situ infrared spectroscopy. Compared with the conventional ZSM-5 zeolite, the hierarchical ZSM-5 zeolite had a lower concentration of surface acid sites. However, the hierarchical structure had more Lewis acid sites and, more importantly, much more external active sites as confirmed by 2,6-di-tert-butylpyridine infrared spectroscopy. Such hierarchical structure exposed more acid sites on the external surface, which subsequently lead to higher catalytic activity in reactions involving bulky molecules, such as o-xylene isomerization.

One-step synthesis of hierarchical mesoporous zeolite Beta microspheres from assembly of nanocrystals

Hierarchical mesoporous zeolite Beta microspheres (Beta-MPs) from assembly of nanocrystals were successfully one-step-synthesized through a simple polymer agent. The Beta-MPs sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption isotherms, and thermogravimetric analysis. The characteristics of the samples are comparable with conventional Beta zeolite. The Beta-MPs with a hierarchical mesoporous structure and a uniform size could be easily separated with filtration. This procedure successfully avoided the high-speed centrifugation of the nano-zeolites during the traditional method. As catalysts, the Beta-MPs showed higher catalytic activity and selectivity than conventional Beta in alkylation of benzene with isopropanol to cumene.