Synthesis of hierarchical ZSM-5 zeolites with CTAB-containing seed silicalite-1 and its catalytic performance in methanol to propylene

Recent Progress on In Situ Catalytic Conversion Catalysts for Oil Shale

With the gradual depletion of oil resources, it is urgent to vigorously develop unconventional and renewable energy sources. As an unconventional resource with abundant resources, the rational and efficient development of oil shale is of great significance to alleviating the national energy crisis. The main methods of oil shale development are surface dry distillation and in situ transformation. In situ catalytic conversion technology, as an emerging mining method, has the potential to improve efficiency, reduce costs, and environmental impact and is an important direction for future oil shale development. As a key component in the in situ conversion process, catalysts play a crucial role in the rate, selectivity, and product quality of the reaction. However, the research on oil shale pyrolysis catalysts is still in the laboratory stage and is difficult to translate into practical applications. Therefore, this paper reviews recent progress of catalyst research in the in situ catalytic conversion of oil shale, including the types, design principles, and reaction mechanisms of catalysts, and looks forward to the future development direction. It provides a certain reference for the discovery of new catalysts that can improve yield and reduce environmental pollution in the process of oil shale extraction and also provides a valuable technical reference for the green development and utilization of unconventional and strategic alternative energy sources in the world and the transformation and sustainable development of the global energy structure.

Distribution of rhizosphere fungi of Kobresia humilis on the Qinghai-Tibet Plateau

Kobresia humilis is a major species in the alpine meadow communities of the Qinghai-Tibet Plateau (QTP); it plays a crucial role in maintaining the ecological balance of these meadows. Nevertheless, little is known about the rhizosphere fungi associated with K. humilis on the Qinghai Tibet Plateau. In this study, we used Illumina Miseq to investigate the fungal diversity, community structure, and ecological types in the root and rhizosphere soil of K. humilis across eight areas on the QTP and analyzed the correlation between rhizosphere fungi of K. humilis and environmental factors. A total of 19,423 and 25,101 operational taxonomic units (OTUs) were obtained from the roots and rhizosphere soil of K. humilis. These were classified into seven phyla, 25 classes, 68 orders, 138 families, and 316 genera in the roots, and nine phyla, 31 classes, 76 orders, 152 families, and 407 genera in the rhizosphere soil. There were 435 and 415 core OTUs identified in root and rhizosphere soil, respectively, which were categorized into 68 and 59 genera, respectively, with 25 shared genera. Among them, the genera with a relative abundance >1% included Mortierella, Microscypha, Floccularia, Cistella, Gibberella, and Pilidium. Compared with the rhizosphere soil, the roots showed five differing fungal community characteristics, as well as differences in ecological type, and in the main influencing environmental factors. First, the diversity, abundance, and total number of OTUs in the rhizosphere soil of K. humilis were higher than for the endophytic fungi in the roots by 11.85%, 9.85%, and 22.62%, respectively. The composition and diversity of fungal communities also differed between the eight areas. Second, although saprotroph-symbiotrophs were the main ecological types in both roots and rhizosphere soil; there were 62.62% fewer pathotrophs in roots compared to the rhizosphere soil. Thirdly, at the higher altitude sites (3,900-4,410 m), the proportion of pathotroph fungi in K. humilis was found to be lower than at the lower altitude sites (3,200-3,690 m). Fourthly, metacommunity-scale network analysis showed that during the long-term evolutionary process, ZK (EICZK = 1) and HY (EICHY = 1) were critical sites for development of the fungal community structure in the roots and rhizosphere soil of K. humilis, respectively. Fifthly, canonical correspondence analysis (CCA) showed that key driving factors in relation to the fungal community were longitude (R2 = 0.5410) for the root community and pH (R2 = 0.5226) for the rhizosphere soil community. In summary, these results show that K. humilis fungal communities are significantly different in the root and rhizosphere soil and at the eight areas investigated, indicating that roots select for specific microorganisms in the soil. This is the first time that the fungal distribution of K. humilis on the QTP in relation to long-term evolutionary processes has been investigated. These findings are critical for determining the effects of environmental variables on K. humilis fungal communities and could be valuable when developing guidance for ecological restoration and sustainable utilization of the biological resources of the QTP.

Resource Utilization of Waste Cooking Oil Catalyzed by Na2CO3/ZSM-5

A catalyst with a simple synthetic process and good catalytic performance was prepared using Na2CO3 as the active component and ZSM-5 as the carrier for the resource utilization of waste cooking oil. The structure of Na2CO3/ZSM-5 was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, and the effects of parameters such as Na2CO3 loading, catalyst percentage, and reaction time on the yield of fatty acid methyl esters were investigated. The results showed that the conversion of waste cooking oil to fatty acid methyl esters yielded up to 96.89% when the Na2CO3 loading was 35%, the reaction temperature was 65 °C, the reaction time was 2 h, and the catalyst percentage was 1 wt %. The Na2CO3/ZSM-5 catalyst could be used to replace H2SO4 or NaOCH3 in the industrial treatment of waste cooking oil for its resource utilization.

The Synergistic Impact of Crystal Seed and Fluoride Ion in the Synthesis of Silicalite-1 Zeolite in Low-Template Systems

Silicalite-1 zeolites are widely applied in gas adsorption, catalysis, and separation due to their excellent hydrothermal stability and unique pore structure. However, traditional preparation methods have inherent drawbacks such as high pollution, high cost, etc. Therefore, this work proposed a green and efficient route for preparing Silicalite-1 zeolite by adding NH4F (F/Si = 0.1) and seeds (10 wt%) in a much shorter time (8 h) in a low-template system (TPA+/Si = 0.007). It was found that NH4F is beneficial for inhibiting the formation of SiO2. The S-1 seeds could drastically induce the formation of the zeolite skeleton structure. Noteworthy, the morphology of zeolites was determined by the relative content of NH4F and seeds. The crystal morphology is determined by the higher content of the two substances; however, when the content is similar, the crystal morphology is determined by NH4F. The results showed that simultaneous control of NH4F and seeds can suppress SiO2 formation, can improve the relative crystallinity of products, and can be precisely regulated via the synergistic effect of both in zeolite morphology. This work not only provides new ideas for regulating the morphology of silicate-1 crystals but also offers a new path for industrial large-scale production of low-cost and efficient zeolites.

Optimization of hierarchical ZSM-5 structure from kaolin as catalysts for biofuel production

Optimization of hierarchical ZSM-5 structure by variation of the first hydrothermal step at different times provides insight into the evolution of micro/mesopores and its effect as a catalyst for deoxygenation reaction. The degree of tetrapropylammonium hydroxide (TPAOH) incorporation as an MFI structure directing agent and N-cetyl-N,N,N-trimethylammonium bromide (CTAB) as a mesoporogen was monitored to understand the effect towards pore formation. Amorphous aluminosilicate without the framework-bound TPAOH achieved within 1.5 h of hydrothermal treatment provides flexibility to incorporate CTAB for forming well-defined mesoporous structures. Further incorporation of TPAOH within the restrained ZSM-5 framework reduces the flexibility of aluminosilicate gel to interact with CTAB to form mesopores. The optimized hierarchical ZSM-5 was obtained by allowing hydrothermal condensation at 3 h, in which the synergy between the readily formed ZSM-5 crystallites and the amorphous aluminosilicate generates the proximity between micropores and mesopores. A high acidity and micro/mesoporous synergy obtained after 3 h exhibit 71.6% diesel hydrocarbon selectivity because of the improved diffusion of reactant within the hierarchical structures.

Hierarchical ZSM-5 zeolite obtained by designed organosiloxane: synthesis, characterization and catalytic applications

Abstract: A new strategy was implemented to synthesize hierarchical ZSM-5 zeolite, which uses self-made Organosilanized Double-terminal Amino Polyetheramine (ODAP) as a soft template to generate mesopores. The influence of the addition amount of ODAP on the textural properties and morphologies of the hierarchical ZSM-5 zeolite were investigated. The obtained hierarchical ZSM-5 zeolite were characterized by XRD, N2 physical adsorption, SEM, NH3-TPD and other methods. The analysis of the experimental results shows that the maximum total BET specific surface area and mesoporous specific surface area of the optimized hierarchical ZSM-5 zeolite reached 609 m2g-1 and 278 m2g-1, respectively. Because the synthesized hierarchical ZSM-5 zeolite has a large mesoporous specific surface area and abundant surface acidity, in terms of reactant conversion and product selectivity, compared with microporous zeolite, it exhibits excellent catalytic performance in the thiophene alkylation desulfurization reaction. This synthesis strategy can be extended to the preparation of zeolites with different framework structures, which is of great significance.

Seed-sol-assisted construction of a coffin-shaped multilamellar ZSM-5 single crystal using CTAB

A coffin-shaped multilamellar ZSM-5 single crystal (CMZS) composed of orderly stacked 2D nanosheets (70-100 nm) was synthesized via the use of cetyltrimethylammonium bromide (CTAB) in the presence of silicalite-1 seed sol. This crystallization strategy opens a facile approach for industrial applications using CMZS in the catalytic conversion of bulky molecules.

Utilization of red mud waste into mesoporous ZSM-5 for methylene blue adsorption-desorption studies

Red mud as industrial waste from bauxite was utilized as a precursor for the synthesis of mesoporous ZSM-5. A high concentration of iron oxide in red mud was successfully removed using alkali fusion treatment. Mesoporous ZSM-5 was synthesized using cetyltrimethylammonium bromide (CTABr) as a template via dual-hydrothermal method, and the effect of crystallization time was investigated towards the formation of mesopores. Characterization using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N₂ adsorption-desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) indicated the formation of cubic crystallite ZSM-5 with high surface area and mesopore volume within 6 h of crystallization. Increasing the crystallization time revealed the evolution of highly crystalline ZSM-5; however, the surface area and mesoporosity were significantly reduced. The effect of mesoporosity was investigated on the adsorption of methylene blue (MB). Kinetic and thermodynamic analysis of MB adsorption on mesoporous ZSM-5 was carried out at a variation of adsorption parameters such as the concentration of MB solution, the temperatures of solution, and the amount of adsorbent. Finally, methanol, 1-butanol, acetone, hydrochloric acid (HCl), and acetonitrile were used as desorbing agents to investigate the reusability and stability of mesoporous ZSM-5 as an adsorbent for MB removal.

Novel synthesis and catalytic performance of hierarchical MOR

A novel route was developed to synthesize hierarchical MOR through introduction of BEA/MOR zeolite embryos as structural growth inducer (SGI) in the presence of hexadecyltrimethylammonium (CTA⁺).

State of the Art and Perspectives of Hierarchical Zeolites: Practical Overview of Synthesis Methods and Use in Catalysis

Microporous zeolites have proven to be of great importance in many chemical processes. Yet, they often suffer from diffusion limitations causing inefficient use of the available catalytically active sites. To address this problem, hierarchical zeolites have been developed, which extensively improve the catalytic performance. There is a multitude of recent literature describing synthesis of and catalysis with these hierarchical zeolites. This review attempts to organize and overview this literature (of the last 5 years), with emphasis on the most important advances with regard to synthesis and application of such zeolites. Special attention is paid to the most common and important 10- and 12-membered ring zeolites (MTT, TON, FER, MFI, MOR, FAU, and *BEA). In contrast to previous reviews, the research per zeolite topology is brought together and discussed here. This allows the reader to instantly find the best synthesis method in accordance to the desired zeolite properties. A summarizing graph is made available to enable the reader to select suitable synthesis procedures based on zeolite acidity and mesoporosity, the two most important tunable properties.

Lower olefins from methane: recent advances

Modern methods for methane conversion to lower olefins having from 2 to 4 carbon atoms per molecule are generalized. Multistage processing of methane into ethylene and propylene via syngas or methyl chloride and methods for direct conversion of CH4 to ethylene are described. Direct conversion of syngas to olefins as well as indirect routes of the process via methanol or dimethyl ether are considered. Particular attention is paid to innovative methods of olefin synthesis. Recent achievements in the design of catalysts and development of new techniques for efficient implementation of oxidative coupling of methane and methanol conversion to olefins are analyzed and systematized. Advances in commercializing these processes are pointed out. Novel catalysts for Fischer – Tropsch synthesis of lower olefins from syngas and for innovative technique using oxide – zeolite hybrid catalytic systems are described. The promise of a new route to lower olefins by methane conversion via dimethyl ether is shown. Prospects for the synthesis of lower olefins via methyl chloride and using non-oxidative coupling of methane are discussed. The most efficient processes used for processing of methane to lower olefins are compared on the basis of degree of conversion of carbonaceous feed, possibility to integrate with available full-scale production, number of reaction stages and thermal load distribution.

The bibliography includes 346 references.

Synthesis of an excellent MTP catalyst: hierarchical ZSM-5 zeolites with great mesoporosity

A unique organosiloxane-polyether amine (OPA) was produced and used as mesoporogen to efficiently synthesize hierarchical ZSM-5 zeolites with great mesoporosity. We have employed silica sol and tetraethylorthosilicate, respectively, to investigate the influence of different silicon sources on hierarchical zeolites in the presence of OPA. The mesopores of synthesized samples focused on 6-15 nm, and the external surface area varied from 185 to 463 m² g^-1 where the micropore surface area was maintained at 245-334 m² g^-1. Benefiting from the superior structure properties, these samples were used as catalysts in the reaction of methanol to propylene, and the optimal one catalysed for 180 h with methanol conversion above 95%. The as-produced OPA could connect steadily with zeolite frameworks through covalent bonds (-Si-O-Si-) during the hydrothermal crystallization process. This type of connection mode could effectively avoid the formation of amorphous phase and the special molecular structure of OPA could efficiently introduce abundant mesopores with few micropores being consumed. The samples synthesized with silicon sol were made up of quasi-circular particles of about 800 nm in size and further consisted of nanocrystals of 40 nm, and the samples produced with TEOS have a particle size of about 1-2 µm aggregated with nanocrystals of 300 nm.

Synthesis and Characterization of Hierarchical ZSM-5 Zeolites with Outstanding Mesoporosity and Excellent Catalytic Properties

A novel soft-template (ST) is fabricated and successfully employed as mesoporogen to synthesis hierarchical ZSM-5 zeolites with outstanding mesoporosity and high hierarchy factors. The as-produced soft-template can connect steadily with the MFI frameworks by covalent bonds of -Si-O-Si- during the high-temperature hydrothermal crystallization process. This type of connection mode can effectively avoid the formation of amorphous materials, and the specific structure of this soft-template can efficiently introduce plentiful of mesopores with few micropores being consumed. The particles of as-synthesized hierarchical ZSM-5 zeolites are in size of about 1 μm, which are made up of nanocrystals of 60-150 nm. The structure parameters of these samples are characterized with the techniques of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, nitrogen sorption, scanning electron microscope (SEM), transmission electron microscope (TEM), NH₃ temperature-programmed desorption (NH₃-TPD) and thermogravimetric (TG). Due to the nature of zeolites and great microporosity, these hierarchical samples present great tolerance of hydrothermal treatment. And because of the intracrystalline mesopores, large external surface areas, and abundant accessible acid sites, whether in conversion rate of reactants or selectivity of products, the hierarchical samples exhibit excellent catalytic performance in the reactions of alkylation between benzene and benzyl alcohol, cracking of 1,3,5-tri-isopropylbenzene, and thermal cracking of low-density polyethylene (LDPE), respectively.