Steam-assisted Crystallization Research Articles

Steam-assisted synthesis of SAPO-34@ZSM-5 core-shell zeolite for enhancing the synergies of n-hexane-Methanol Co-Reaction to light olefins

An alternative and promising route for the production of light olefins which realizes the objective of effective resource usage is the coupling conversion of n -hexane-methanol. The SAPO-34@ZSM-5 core-shell composite has been designed and fabricated by the steam-assisted crystallization (SAC) method for boosting the n -hexane-methanol synergies. SAC avoids the undesired phase transformation/dissolution of SAPO-34 caused by exposure to harsh basic conditions of the ZSM-5 precursor solution. In comparison with the nanosized ZSM-5 or physical mixture, the SAPO-34@ZSM-5 core-shell zeolite demonstrates a 32–38 wt% increase in the light olefin selectivity, a 28–67 wt% increase in the n -hexane conversion, and an 89–143% improvement in the catalyst lifetime under identical reaction conditions. With the aid of GC-MS analysis of carbonaceous deposits in spent catalysts, higher polymethylbenzenes concentration and lower polycyclic aromatic hydrocarbon (PHA) concentration are obtained from the extracted species of spent SAPO-34@ZSM-5 in comparison with that of other samples, which suggests the aromatic-based route to light olefins is enhanced and the carbonaceous deposition is slowed down. The core-shell configuration of the SAPO-34@ZSM-5 composite diminishes the diffusion rate of methanol towards the SAPO-34 core layer and increases the coupling of n -hexane derivatives with methanol in the hydrocarbon pool (HCP) route. The decreased number of acidic sites on the external surface of the SAPO-34 core layer may also be accounted for the inhibited carbon deposition. • SAPO-34@ZSM-5 is synthesized firstly by a steam-assisted crystallization method. • Core-shell structure of SAPO-34@ZSM-5 enhances the synergistic effect of reactants. • Core-shell structure of SAPO-34@ZSM-5 slows down coking inside the SAPO-34 core layer. • A synergistic path for n-hexane-methanol co-reaction on SAPO-34@ZSM-5 is proposed.

Methanol aromatization over Zn-modified HZSM-5 catalysts derived from ZIF-8

Methanol to aromatics (MTA) is an effective way to produce aromatics by non-petroleum route. The acidity and structure of zeolite catalysts are the key to aromatics yield and stability of catalysts in MTA reaction. Here, Zn-modified HZSM-5 catalysts were prepared by physical mixing method (PM), in-situ hydrothermal synthesis method (SH) and steam-assisted crystallization method (SAC) using ZIF-8 as sacrificial template and Zn source. XRD, SEM, TEM, N2 adsorption-desorption, ICP-OES, NH3-TPD, Py-IR, XPS, H2-TPR, TG characterization methods were used to investigate the physical and chemical properties of the catalysts. The influence of preparation methods of catalysts, the addition amount of ZIF-8, different Zn sources and reaction conditions on the products distribution in MTA reaction were investigated. The results showed that the crystallinity of ZnZ8(SAC)/Z5 catalyst was improved and the hierarchical pore structure was obtained successfully after introduced ZIF-8 by steam-assisted crystallization method. Among them, ZnZ8 mainly exists as ZnOH+ species, which improved the utilization rate of Zn atoms and more L acid sites and moderate acid concentration were formed. The addition amount of ZIF-8 can affect the crystalline size, pore structure and the concentration of ZnOH+ species of ZnZ8(SAC)/Z5. An appropriate ratio of B/L acid concentration was formed when adding an appropriate amount of ZIF-8. Compared with the traditional Z5 catalyst modified with Zn(NO3)2 as Zn source (1% ZnZN(SAC)/Z5), there are smaller particle size, larger specific surface area and mesopore volume as well as suitable acid distribution in 1% ZnZ8(SAC)/Z5 catalyst. The preparation method of catalyst, the addition amount of ZIF-8, different Zn sources and reaction conditions have a significant effect on the selectivity of BTX.

Controllable hollow HZSM-5 for high shape-selectivity to light aromatics from catalytic reforming of lignite pyrolysis volatiles

Light aromatics could be produced by catalytic fast pyrolysis (CFP) of lignite over HZSM-5 with shape selectivity and accessible active sites. However, the catalytic reactivity in the center crystal has not been fully exploited. In this work, the different hollow hierarchical porosity-tunable ZSM-5 were synthesized using polyethylene glycol as a soft template by a steam-assisted crystallization process. Compared with commercial HZSM-5, the synthesized HZSM-5 exhibited higher selectivity for alkylbenzene (toluene and m/p-xylene) with the yield of 9.91 mg/g (7.31 mg/g over commercial HZSM-5). The hollow HZSM-5 with pore-size fine-tuning were favorable to control the tiny different intermediates for shape-selective of benzene and alkylbenzene in CFP. In addition, the unmodified synthetic hollow catalysts also kept highly stability after seven cycle experiments due to the enhancement of molecules diffusion in crystal center, especially the alkylbenzene yield was sustained at approximately 7.38 mg/g during cycle experiments. The work provides a great prospect to promote the formation of alkyl aromatics in CFP.

Utilization of zeolite H-MOR based on bagasse ash silica as a catalyst for the hydrolysis reaction of cassava peel cellulose for glucose production

Bagasse and cassava peel are waste that can be increased economic value. In this study, we have successfully synthesized zeolite H-MOR from sugarcane bagasse ash (SCBA) silica using the Steam-Assisted Crystallization (SAC) method at 170°C for 120 hours and determined its catalytic activity on the hydrolysis of cassava peel starch to produce glucose. H-MOR synthesized using LUDOX (commercial silica) was used as a comparison. The results showed that the MOR zeolite synthesized using SCBA and LUDOX silica had a crystallinity of 92.12% and 81.17%, respectively. The cellulose content in cassava peel flour is 57.8%. Optimization of the catalytic test variable showed that the hydrolysis of cellulose occurred at 140°C for 4 hours with a 1: 1 ratio of catalyst and substrate. The glucose concentrations obtained from cellulose hydrolysis using zeolite H-MOR catalyst from SCBA and Ludox were 398.5 ppm and 237.45 ppm with conversion degrees of 60.4% and 61.2%, respectively.

Rational Design of Pomegranate-like Base-Acid Bifunctional β Zeolite by Steam-Assisted Crystallization for the Tandem Deacetalization-Knoevenagel Condensation.

A highly crystalline pomegranate-like base-acid bifunctional beta zeolite was successfully synthesized by the steam-assisted crystallization method using a basic nitrided N-beta as the starting material. The secondary crystal growth of a beta zeolite generating acid functionality occurred over the outer surface and intercrystalline void spaces of the N-beta zeolite. The pomegranate-like N-beta@H-beta zeolite had a high surface area and base-acid dual functionality because of the well-connected framework topologies of the H-beta and N-beta crystallites. The N-beta@H-beta zeolite exhibited a superior yield of benzylidenemalononitrile during the tandem deacetalization-Knoevenagel condensation of benzaldehyde dimethyl acetal and malononitrile compared to H-beta, N-beta, and their physical mixture. This is likely due to the isolated and balanced activity of the base- and acid-catalyzed reactions.

Dichloromethane catalytic combustion over Co3O4 catalysts supported on MFI type zeolites

Three different MFI type zeolites Silicalite-1, ZSM-5 and TS-1 as supports were synthesized by steam-assisted crystallization method. Then, the as-synthesized zeolites were used to prepare Co 3 O 4 supported MFI type zeolite catalysts by wet impregnation. The as-prepared Co 3 O 4 supported MFI type zeolite catalysts possessed high specific surface area, abundant pore structure and surface acidity. Finally, the as-prepared catalysts were used for dichloromethane (DCM) catalytic combustion and the results showed that Co 3 O 4 supported MFI type zeolite catalysts had better performance than pure Co 3 O 4 . The synergistic catalytic effects between MFI type zeolite and Co 3 O 4 effectively reduced the formation of polychlorinated by-products and suppressed the deactivation of catalyst during the catalytic combustion of DCM. And Co 3 O 4 /ZSM-5 catalyst exhibited the best performance due to its proper Brønsted acid sites amount and the T 90 (the reaction temperature at which the dichloromethane conversion reached 90%) was 370 °C at 1000 ppm DCM, 10% O 2 /N 2 and the gas hourly space velocity of 30,000 mL/(g∙h). • The Co 3 O 4 supported MFI type zeolites were synthesized by impregnation method. • The zeolite as support restrained the deactivation of Co 3 O 4 catalyst during DCM catalytic combustion. • The surface acid sites of zeolite restrained the polychlorinated byproducts formation. • Co 3 O 4 /ZSM-5 exhibited the best performance for the catalytic combustion of DCM.

Combination of spray drying encapsulation and steaming transformation toward robust hierarchical zeolite microspheres: Synthesis, formation mechanism and acid catalysis

Binder-free zeolite microspheres with hierarchical porosities are prepared by combining spray-drying encapsulation and steaming transformation. Amorphous aluminosilicate microspheres encapsulating tetrapropylammonium hydroxide (TPAOH) are first synthesized by spray drying. Then, they are successfully transformed into robust zeolite microspheres by using a steam-assisted crystallization (SAC) process. The drying temperature plays a decisive role in encapsulation and preservation of TPAOH guiding zeolite crystallization, as well as the morphology and sizes of the obtained zeolites. The morphology, structure and crystallinity of the resulted zeolites can also be controlled by adjusting the water/gel mass ratio and SAC time. The detailed structure and crystallization evolution over the SAC transformation process is studied and discussed. The typical obtained zeolite microspheres possess surface buckled morphologies, uniform large particle sizes, hierarchical porosities, good mechanic strength and intrinsic strong acid sites. They demonstrate enhanced catalytic activity and stability in acid catalytic aldol condensation.

Cost-effective synthesis of hierarchical HZSM-5 with a high Si/TPA+ ratio for enhanced catalytic cracking of polyethylene

In this work, hierarchical HZSM-5 zeolites, with the high Si/TPA+ ratio of 34 and Si/Al ratios of 100 and 30, have been synthesized by the mesoporogen-free, Na+-free, and steam-assisted crystallization route using industrial silica sol as the silicon source. Highly crystalline HZSM-5 (30)-34 sample inherited the strong acidity of conventional HZSM-5 and exhibited the relatively large mesopore volume (0.08 ​cm3 ​g−1). With this structure, the accessibility of Brønsted acidity sites is increased from 6.25% of conventional HZSM-5 to 64.3% of HZSM-5 (30)-34, which enhanced the catalytic cracking performance of low-density polyethylene (LDPE). As a result, the decomposition temperature of LDPE was reduced to 420 ​°C, which is apparently lower than 482 ​°C when no catalyst was adopted. Moreover, the HZSM-5 (30)-34 sample showed good reusability and catalytic stability in the regeneration-recycle experiments.

Tungstophosphoric acid incorporated hierarchical HZSM-5 catalysts for direct synthesis of dimethyl ether

HZSM-5 zeolites are active materials in dimethyl ether (DME) production with high surface acidity. In this study, hierarchical HZSM-5 catalysts were synthesized with steam-assisted crystallization (SAC) method and then in order to increase its surface acidity, TPA was loaded into the HZSM-5 catalyst having various mass ratios (5, 10, 25%) by wet impregnation method. Synthesized catalysts were characterized by N2 physisorption (BET analysis), X-Ray diffraction and pyridine adsorbed diffuse reflectance FTIR spectroscopy techniques. Characterization analysis of tungstophosphoric acid (TPA) impregnated catalysts indicated that hierarchical HZSM-5 possesses mesoporous structures. The average pore size distribution of TPA impregnated HZSM-5 catalysts were between 17 and 20 nm. TPA impregnation promoted Brønsted acid sites of the catalyst, which favors methanol dehydration reaction. Activity tests have been performed at reaction temperatures of 200–300 °C at 50 bar reaction pressure in the presence of admixed catalysts (physically mixed commercial HifuelR-120 and HZSM-5 based catalysts with a weight ratio of 1:1). Results revealed that the increase in the amount of heteropoly acid has enhanced DME selectivity and CO conversion. Maximum DME selectivity of 57% and CO conversion of 46% were achieved in the presence of the 25TPA@HZSM-5 catalyst at the optimum reaction temperature of 275 °C. TGA analysis result of spent catalysts presented the highest amount of coke over HZSM-5. TPA incorporation decreased coke formation due to suppression of the Lewis acid site, which is responsible for the coke formation.

Ga-Supported MFI Zeolites Synthesized Using Carbon Nanotubes Containing Gallium Oxide Nanoparticles on Exterior Walls and in Interior Channels as Hard Templates for Methanol Aromatization

A combinative approach of steam-assisted crystallization and hard templating was employed to prepare mesostructured Ga/ZSM-5 catalysts. Carbon nanotubes (CNTs) containing gallium oxide nanoparticle...

Zn-based metal–organic frameworks as sacrificial agents for the synthesis of Zn/ZSM-5 catalysts and their applications in the aromatization of methanol

Zn/ZSM-5 was prepared by using a combinative method of steam-assisted crystallization (SAC) and hard templating. Zn-based MOFs, including coordination polymer of Oslo number 1-Zn (CPO-1-Zn) and zeolitic imidazolate framework-8 (ZIF-8), were used as the sacrificial agents. These MOFs-derived catalysts were compared with Zn/ZSM-5 made by impregnation. Physicochemical characterization revealed that all Zn/ZSM-5 catalysts had finely dispersed Zn2+ species, i.e., ZnO and Zn(OH)+. However, the concentration of Lewis acidic Zn2+ species and the compositions of Zn(OH)+ and ZnO were different. Applying ZIF-8 as the sacrificial agent generated a higher concentration of Lewis acidic Zn2+ species and a higher ratio of Zn(OH)+-to-ZnO in Zn/ZSM-5, which showed a better performance in the aromatization of methanol.

Steam-Assisted in Situ Prepared TS-1 with Hierarchical Pores and Tunable Acid Sites Grown on Carbon Nanotubes Decorated Nickel Foam

The TS-1 particles grown on carbon nanotubes decorated nickel foam (denoted as MTS-1S) are successfully synthesized by a steam-assisted crystallization method that does not waste the gels and is mo...

Hybridization of ZSM‐5 with Spinel Oxides for Biomass Vapour Upgrading

AbstractIn this study, we report catalytic fast pyrolysis of biomass using multifunctional hybrid spinel‐oxide@zeolite catalysts prepared by using the steam‐assisted crystallization (SAC) method to create the mesoporous zeolite followed by urea hydrolysis of metal nitrates to deposit spinel‐oxides. This hybrid catalyst was quite effective in the deoxygenation of pinewood sawdust pyrolysis vapours, while avoiding over cracking of the lignin precursors, which are already ideal as chemical and fuel precursors. In the first step, multiple spinel oxides MgB2O4 (where B=Fe, Al, Ce, Ga, Cr) were screened as catalysts for the pyrolysis of pinewood sawdust and the resultant bio‐oil (bio‐oil on the water‐free basis) was assessed in terms of carbon efficiency, oxygen content and chemical composition. While all the tested spinel oxides deoxygenated the pyrolysis vapour, MgAl2O4 and MgFe2O4 were found to provide a well‐balanced deoxygenation degree and producing bio‐oil with acceptable carbon efficiency. Catalytic activity and product distribution were affected by the density and strength of the acid sites of the spinel oxides. Subsequently, CFP over MgFe2O4@ZSM5 and MgAl2O4@ZSM5 was investigated under similar condition. The better performance of the hybrid catalyst was attributed to the deposition of small particles of MgFe2O4 in the external surface of the zeolite. The presence of this spinel oxide on the external surface depolymerized bulky oxygenates to lighter fractions that could easily access the active sites within the mesoporous structure of the zeolite, thus providing the catalytic function needed for the oxygen removal after aromatic ring saturation.

In situ fabrication of core–shell-structured Beta@Silicalite-1 catalysts by a novel steam-assisted crystallization strategy

A green and efficient steam-assisted crystallization (SAC) strategy was employed to synthesize a core–shell zeolite with different frameworks between the core and shell, Beta@Silicalite-1.

Fast synthesis of SSZ-13 zeolite by steam-assisted crystallization method

Abstract The crystallization time of SSZ-13 was shortened from several days to 6 h without seeding or pre-aging at conventional synthetic temperature. The fast synthesis was realized by converting a clear-sol derived dry gel with the assistance of steam at 160 °C with a high yield (86%). The crystals of fast synthesized SSZ-13 appeared much smaller in size (333 ± 52 nm) compared to its bulk conventional counterpart. The effects of synthetic parameters such as silica sources, water to dry-gel ratio, aluminum content and inorganic cations were investigated. It was concluded that appropriate chosen of silica source and water to dry-gel ratio was the key to accelerate the formation of SSZ-13. The fast-synthesized SSZ-13 was tested with the reaction of methanol to olefins and showed a more than twofold increase in catalyst lifetime and higher selectivity to olefins than that of the conventional SSZ-13.

Hierarchical mesoporous ZSM-5 supported nickel catalyst for the catalytic hydrodeoxygenation of anisole to cyclohexane

Upgrading of bio-oil through catalytic hydrotreating was investigated with anisole as a model compound. Hierarchical ZSM-5 zeolites with nano-crystalline structure were successfully synthesized by a segmented steam-assisted crystallization method by tuning the rate of crystallization during the phase transforming between the amorphous structure and crystalline structure without using the organic template. The diffusional properties of ZSM-5 samples were investigated by catalytic cracking of 1,3,5-TIPB. Ni/hierarchical ZSM-5 catalysts displayed an excellent performance in the hydrodeoxygenation (HDO) of biomass-derived anisole to cyclohexane in comparison with conventional Ni/ZSM-5 catalyst. The activity and selectivity were significantly improved by enhancing the accessibility of acidities. Anisole HDO mainly follows the anisole to benzene with metal sites by direct deoxygenation, then cyclohexane formed by hydrogenation.

Efficient synthesis of high silica SSZ-13 zeolite via a steam-assisted crystallization process

High silica SSZ-13 zeolite was synthesized by an efficient and green steam-assisted crystallization (SAC) method under a low alkalinity and low organic templates amount system. The as-prepared samples were characterized by XRD, SEM, N2 adsorption–desorption, TG–DTG and NH3-TPD. The results showed that the SAC method can not only remarkably improve zeolite yield but also enhance the crystallization rate of SSZ-13 zeolite compare to conventional hydrothermal route. Meanwhile, it was also found that the various content of the organic structure directing agent (N,N,N-trimethyladamantammonium hydroxide, TMAdaOH) in the dry gel can adjust flexibly the crystal size, morphology and acidity of samples. The zeolite samples with smaller particles and more strong acidity amount were more likely obtained under the higher TMAdaOH/SiO2 ratio (0.2) condition. In addition, the catalytic evaluation in methanol-to-olefins (MTO) reaction showed that the high silica SSZ-13 catalysts synthesized by SAC method exhibited longer lifetime and comparative selectivity to ethylene and propene than those of the SSZ-13s obtained by conventional hydrothermal route. Thus, the SAC route is believed to be a competitive strategy to synthesize high silica SSZ-13 zeolites with improved MTO catalytic performance.

Gallium-Immobilized Carbon Nanotubes as Solid Templates for the Synthesis of Hierarchical Ga/ZSM-5 in Methanol Aromatization

Hierarchical Ga/ZSM-5 was synthesized by using a combinative method of steam-assisted crystallization (SAC) and hard templating. Ga-immobilized carbon nanotubes (GaCNTs) were used as hard templates. Compared with Ga-doped ZSM-5 catalysts made by impregnation and by sequential CNT templating and impregnation, hierarchical Ga/ZSM-5 had a moderate mesoporosity and possibly a high concentration of (GaO)+-Bronsted acid site. The moderate mesoporosity shortens residence times of products in the ZSM-5 matrix, while the high concentration of (GaO)+-Bronsted acid enhances aromatization activity. These advantages are critical to improve catalytic performance and durability of hierarchical Ga/ZSM-5 in methanol aromatization.

A large-surface-area TS-1 nanocatalyst: a combination of nanoscale particle sizes and hierarchical micro/mesoporous structures.

By a simple sequent process of dry-gel steam-assisted crystallization and following a top-down alkali-etching treatment, hierarchically structured TS-1 nanozeolites (nanoTS-1_D) with abundant micro/mesopores have been synthesized for the first time, and they exhibit remarkably high specific surface area of 606 m2 g−1 and pore volume of 0.86 cm3 g−1. Characterization by XRD, FTIR, UV-vis and EM confirm the exclusive incorporation of titanium species in zeolite frameworks. More importantly, compared with the microporous TS-1 nanocrystal material with identical particle sizes of 80 nm (nanoTS-1) and submicrometer-sized mesoporous TS-1 material (mesoTS-1), here the reported nanoTS-1_D catalyst shows greatly improved performance in the model reaction of 1-hexene epoxidation. 40.9% olefin conversion and 96.3% epoxide selectivity are achieved and its high stability is verified by the 6 recycling–regeneration tests.

Direct conversion of syngas to isoparaffins over hierarchical beta zeolite supported cobalt catalyst for Fischer-Tropsch synthesis

A hierarchical micro-meso-macroporous Beta zeolite (HB) was developed by a steam-assisted crystallization method and was employed for cobalt Fischer-Tropsch synthesis. Meso-macroporous silica (HS), alumina modified meso-macroporous silica (HAS) and conventional Beta zeolite (CB) were used for comparison. Structural characterization indicated that the as-synthesized HB exhibited nanosized Beta zeolite crystallites and a hierarchical micro-meso-macroporous structure. The HB supported catalyst showed very high isoparaffins selectivity because of the isomerization reaction at the strong acidic sites of the Beta zeolite, while due to its good macroporous structure, which is in favor of reducing the internal diffusion limitations, the methane selectivity was kept as low as HAS supported catalysts. In this paper, we use large particle catalysts for evaluation, which are very close to industrial condition. And the conclusions obtained may be very important for the design of new Fischer-Tropsch catalysts.