Framework Of Molecular Sieves Research Articles

Spatial isolation effect improves the acidity and redox capacity of ZSM-5 encapsulating Pt catalyst to achieve efficient toluene oxidation

This paper introduces a novel approach of encapsulating Pt nanoparticles within the pores of a molecular sieve. By comparing the dispersion, reducibility and surface acid sites, the effect of the combination of molecular sieves and Pt particles on the catalytic performance of toluene was studied. The findings demonstrate that Pt nanoparticles were encapsulated within the molecular sieve framework of ZSM-5 molecular sieves using an in-situ synthesis method, exhibiting remarkable catalytic activity towards toluene oxidation (T90=172 ℃). Mainly due to the spatial confinement of the ZSM-5 molecular sieve framework reduces the size of Pt nanoparticles, enhances their dispersion of the Pt@ZSM-5 catalysts. In addition, the space separation effect of ZSM-5 on Pt metal enhances their interaction and promotes the valence state conversion of Pt species. It leads to a large number of acid sites and oxygen vacancies in the catalyst, which improves the adsorption and migration of toluene, thereby improving the catalytic activity. This study will provide valuable insights into the preparation of new nanocatalysts and the catalytic treatment of toluene.

High-temperature treatment promotes N2O decomposition over Fe-impregnated Al-rich SSZ-13 zeolites

Fe/SSZ-13 catalysts were prepared via the impregnation method and calcined at different temperatures. The catalytic activity of Fe/SSZ-13 catalysts in the N2O catalytic decomposition reaction was greatly influenced by the calcination temperature. As the calcination temperature rose to 800 °C, the catalytic efficiency of N2O decomposition performance gradually improved. Nevertheless, if the temperature of calcination exceeded 800 °C, the efficiency diminished as a result of the disintegration of the molecular sieve framework. Various characterization methods were used to investigate the impact of calcination temperature on iron species. The results showed that the high-temperature treatment could promote the dispersion and reduction of Fe2O3 particles on the catalyst surface, which led to the generation of more active species (such as Fe3O4 and FeO) and provided more oxygen vacancies which favored the N-O breakage, thus improving the N2O decomposition activity.

Sulfadiazine removal efficiency with persulfate driven by electron-rich Cu-beta zeolites

Surface electron transport and transfer of catalysts have important consequences for persulfate (PS) activation in PS system. In this paper, an electron-rich Cu-beta zeolites catalyst was synthesized utilizing a straightforward solid-state ion exchange technique to efficiently degrade sulfadiazine. The X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR) results revealed that Cu element substitutes Al element and enters the beta molecular sieve framework smoothly. Furthermore, the X-ray photoelectron spectroscopy (XPS) measurements demonstrated that the Cu-beta catalyst is primarily Cu0. Cu-beta zeolites catalyst can exhibit excellent catalytic activity to degrade sulfadiazine with the oxidant of PS. The optimal sulfadiazine removal performance was explored by adjusting reaction parameters, including sulfadiazine concentration, catalyst dosage, oxidant dosage, and solution pH. The sulfadiazine removal efficiency in the Cu-beta zeolites/PS system could reach 90.5% at the optimal reaction condition ([PS]0 = 0.5 g/L, [Cu-beta zeolites]0 = 1.0 g/L, pH = 7.0) with 50 mg/L of sulfadiazine. Meanwhile, The degradation efficiency was less affected by anionic interference (Cl−, SO4−, HCO3−). The surface electron transport and transfer of the Cu-beta zeolites catalyst were significant causes for the remarkable degradation performance. According to electron paramagnetic resonance (EPR) and quenching studies, the Cu-beta zeolites/PS system was mostly dominated by SO4•- in the degradation of sulfadiazine. Furthermore, two possible pathways for sulfadiazine degradation were proposed according to the analysis of intermediate products detected by the liquid chromatography–mass spectrometry (LC-MS).

Inhibition of terminal C[sbnd]C bonds cleavage drives high selectivity of n-alkane hydroisomerization

Herein we develop a solvent-free one-pot synthesis strategy to simultaneously modify the size effect of metal sites and structural acidity on bifunctional catalysts to in-situ grow platinum nanoparticles (Pt-NPs ∼ 1 nm and ∼ 20 nm) of disparate sizes in the molecular sieve framework without relying on any ligand assistance, causing skeletal defects while exhibiting excellent catalytic performance in n-alkane hydroisomerization. It maintains almost 100 % isomerization selectivity at conversions below 90 %, with performance far superior to that of the conventional catalysts (Pt-NPs ∼ 1 nm). The reason for high selectivity and high liquid yields was revealed by structural characterizations and density functional theory calculations, i.e., the inhibition of terminal CC bond cleavage over n-dodecane chains adsorbed on the defect-containing catalysts and the higher energy barrier of transition state for producing gaseous small molecules, while the size of Pt-NPs may not be the main factor in determining the performance of n-alkane hydroisomerization.

Thick pore walls mesoporous silicon composites based on phosphomolybdic acid: An efficient catalyst for oxidation desulfurization reaction

In this paper, phosphomolybdic acid (HPMo) solution was chosen as a synthetic medium and active ingredient to replace hydrochloric acid, and the thick porous wall silicon composite based on HPMo (HPMo@OMS) was prepared by the one-step co-condensation method, which simplified the preparation process and improved the stability of the molecular sieve framework structure. The composite materials have the same ordered 2D hexagonal mesoporous structure as SBA-15. Compared to the traditional SBA-15 loaded HPMo (HPMo@SBA-15) synthesized in hydrochloric acid solution, the characterization results showed that the pore wall thickness of HPMo@OMS is about 2 nm thicker than the HPMo@SBA-15. Under mild experimental conditions, the catalyst has high desulfurization activity, and the removal rate of sulfur-containing substrate reaches 100%. In addition, after 10 desulfurization cycles, the Mo content of the composites recovered by centrifugation 13.74HPMo@OMS was only 1.67% by ICP-AES, the results after ten cycles of experiments showed that the removal rate of DBT could still reach 93.5%.

Hydroisomerization of n-Hexadecane Over Nickel-Modified SAPO-11 Molecular Sieve-Supported NiWS Catalysts: Effects of Modification Methods.

The complexation-excessive impregnation modification method, which was original in this study, and the ion-exchange method and the in situ modification method were used to synthesize Ni-modified SAPO-11 molecular sieves. With the Ni-modified SAPO-11 samples as support, the corresponding NiWS-supported catalysts for the hydroisomerization of n-hexadecane were prepared. The effects of Ni-modification on SAPO-11 characteristics and the active phase were studied. The structure, morphology, and acidity of SAPO-11, as well as the interaction between active metals and support, the morphology, dispersibility, and stacking number of the active phase, were all changed by Ni-modification methods. The complexation-excessive impregnation modification method deleted a portion of Al from SAPO-11 molecular sieves while simultaneously integrating Ni into the skeletal structure of the surface layer of SAPO-11 molecular sieves, considerably enhancing the acidity of SAPO-11 molecular sieves. Furthermore, during dealumination, ethylenediaminetetraacetic acid generated more mesoporous structures and increased the mesoporous volume of SAPO-11 molecular sieves. Because the complexation-excessive impregnation modification method increased the amount of Ni in the surface framework of the SAPO-11 molecular sieve, it has weakened the interaction between the active phase and the support, improved the properties of the active phase, and greatly improved the hydroisomerization performance of NiW/NiSAPO-11. The yield of i-hexadecane of NiW/NiSAPO-11 increased by 39.3% when compared to NiW/NiSAPO-11. It presented a realistic approach for increasing the acidity of SAPO-11, reducing the interaction between active metals and support, and improving the active phase stacking problem.

Expanded titanosilicate MWW-related materials synthesized from a boron-containing precursor as an efficient catalyst for cyclohexene oxidation

Titanosilicate forms of expanded MWW-related materials (Ti-MWW-exp) are synthesized starting from a lamellar boron-containing MWW precursor. The boron expulsion by the nitric acid treatment from the molecular sieve framework left behind the vacancies. By extending the acid treatment time, Si species around the defects is dissolved and is the likely source for the species required to expand the interlayer space. The obtained Ti-MWW-exp material exhibits a superior catalytic activity in cyclohexene oxidation, and a high selectivity for cyclohexene oxide is also achieved. Moreover, this convenient post synthesis was also used in the preparation of interlayer expanded B-MWW and B–Al-MWW materials, giving rise to the design of the other interlayer expanded metallosilicates. A facile strategy is put forward to construct the interlayer expanded MWW-type metallosilicates. The interlayer expanded Ti-MWW-exp zeolite can exhibit the excellent catalytic performance in the epoxidation of bulky cyclohexene. • An interlayer expanded MWW-type metallosilicate is post-synthesized. • Removal of boron can change the stability of the neighboring Si species. • Si species reinserted into the zeolite can serve as pillars in the interlayer space. • The interlayer expanded Ti-MWW-exp is an efficient catalyst for the cyclohexene oxidation. • This strategy is a promising way for designing other interlayer expanded boron-containing zeolites.

An Ion-Imprinting Derived Strategy to Synthesize Single-Atom Iron Electrocatalysts for Oxygen Reduction.

Carbon-based single-atom catalysts (CSACs) have recently received extensive attention in catalysis research. However, the preparation process of CSACs involves a high-temperature treatment, during which metal atoms are mobile and aggregated into nanoparticles, detrimental to the catalytic performance. Herein, an ion-imprinting derived strategy is proposed to synthesize CSACs, in which isolated metal-nitrogen-carbon (Me-N4 -Cx ) moiety covalently binds oxygen atoms in Si-based molecular sieve frameworks. Such a feature makes Me-N4 -Cx moiety well protected/confined during the heat treatment, resulting in the final material enriched with single-atom metal active sites. As a proof of concept, a single-atom Fe-N-C catalyst is synthesized by using this ion-imprinting derived strategy. Experimental results and theoretical calculations demonstrate high concentration of single FeN4 active sites distributed in this catalyst, resulting in an outstanding oxygen reduction reaction (ORR) performance with a half-wave potential of 0.908V in alkaline media.

Water-Induced Structural Dynamic Process in Molecular Sieves under Mild Hydrothermal Conditions: Ship-in-a-Bottle Strategy for Acidity Identification and Catalyst Modification.

Water is the most important substance in nature. Imitating the formation of natural materials, molecular sieves have been synthesized under hydrothermal conditions and applied in industry. Herein, we reveal an unforeseen observation on a very special water-induced structural dynamic process of these materials. Dynamic and reversible breaking and forming of T-O-T bonds in silicoaluminophosphate (SAPO) occurs through interactions between gaseous water and the molecular-sieve framework under mild hydrothermal conditions and is confirmed by detection of the incorporation of 17 O from H2 17 O into molecular-sieve framework. Encapsulation of the bulky molecules trimethylphosphine and pyridine (kinetic diameters much larger than the pore size of SAPO-34) into CHA cavities consolidated the water-induced dynamic process. Consequently, new insights into the dynamic features of molecular sieves in water are provided. The ship-in-a-bottle strategy based on these findings also open new fields for fine acidity identification and gives extra boost in shape-selective catalysis.

A comparative study of hydrothermal aging effect on cerium and lanthanum doped Cu/SSZ-13 catalysts for NH3-SCR

Ce- or La-doped Cu/SSZ-13 catalysts were prepared by a hydrothermal method and Cu, Ce or La ions were incorporated through stepwise ion exchange. The catalyst activity was measured for the ammonia selective catalytic reduction reaction. The structure and composition of catalyst were characterized by using X-ray diffraction, scanning electron microscopy, inductively coupled plasma mass spectrometry solid-state NMR, NH3-TPD techniques, and the active components were examined by XPS and XANES. The results indicate that the Ce and La doping can both completely preserve the SCR activity of Cu/SSZ-13 above 300 °C, but there is also a decrease of activity below 200 °C. On the other hand, Ce doping is beneficial to the formation of framework aluminum, stabilizes molecular sieve framework and Cu active sites of Cu/SSZ-13, thereby improves the catalyst hydrothermal stability. But La doping will decrease the amount of framework aluminum and Cu active sites of Cu/SSZ-13 after hydrothermally aging, even destroy zeolite CHA structure. This is quite harmful to the catalyst hydrothermal stability.

Rice husk assisted like-dry-gel synthesis of FeSAPO-44 molecular sieve from natural bauxite

In this study, a series of FeSAPO-44 molecular sieves are synthesized by a facile like-dry-gel method. The untreated bauxite is used as the source of Al, Si, while Fe element is retained as the acid site. Rice husks are provided for auxiliary Si source together with Si-sol to balance Al/Si ratio, and its cellulose plays a role in favoring Fe of bauxite into the framework of molecular sieves. The referred sample derived from pseudo-boehmite confirms rice husk facilitates Fe enter the skeleton. The referred sample synthesized from ethyl cellulose further affirmed the function of cellulose. The crystal structure, surface area, pore diameter, surface properties and acidity of samples are systematically characterized. Furthermore, the obtained FeSAPO-44 molecular sieve from natural source of bauxite and rice husk is used as a carrier to support Mo for the hydrocracking of Karamay super heavy oil, which shows a feasible practical application.

Zeolite Synthesis under Nonconventional Conditions: Reagents, Reactors, andModi Operandi

A myriad of tetrahedral molecular sieve frameworks, often siliceous, can be calculated in silico. Only a tiny fraction (<0.1%) of these can be synthesized on purpose. Only a small fraction of these...

A Novel Method for Synthesizing p-Benzoquinone by Direct Catalytic Oxidation of Benzene with Hydrogen Peroxide over Copper-Doped TS-1

Existing methods for synthesizing p-benzoquinone have drawbacks with respect to environmental protection, production scale, or industrial value. Therefore, it is imperative that a simple and environmentally friendly alternative be developed. The approach that involves preparing p-benzoquinone by the catalytic oxidation of benzene with hydrogen peroxide (H2O2) over copper-modified titanium silicalite-1 (Cu/TS-1) has a certain superiority due to its green synthesis and mild reaction conditions. In this study, Cu/TS-1 catalyst was prepared by the wet impregnation of TS-1 with an aqueous solution of Cu(NO3)2 and then characterized by X-ray diffraction, Fourier transform infrared spectroscopy, diffuse reflectance UV–Vis spectroscopy, scanning electron microscopy, inductively coupled plasma mass spectrometry, X-ray fluorescence, and analysis of the N2 adsorption–desorption isotherms. The results reveal that Cu species exist mainly in the form of amorphous CuO that is well dispersed on the surface of catalysts, with no major change in the molecular sieve framework. After optimizing the reaction conditions, a desirable p-benzoquinone selectivity (88.4%) and benzene conversion (18.3%) were obtained when the doping of Cu in Cu/TS-1 is 1.95 wt%. In addition, Cu/TS-1 can be conveniently regenerated, showing a slight decrease in catalytic capability after initial use, which then stabilizes in subsequent circulations. The satisfactory stability and low cost of synthesizing Cu/TS-1 give this method considerable potential for further industrialization.

Preparation and Characterization of Chitosan-Zeolite Molecular Sieve Composite for Ammonia and Nitrate Removal

A new zeolite molecular sieve modified with chitosan was prepared and employed for the adsorption of ammonia and nitrate from underground water. Batch of experiments were performed to investigate the effects of various conditions on chitosan/ zeolite molecular sieve(CTS-Z) preparation, including the concentration of acetic acid, the concentration of chitosan, the stirring time and the stirring temperature. Characteristic of CTS-Z adsorption particles were analyzed by Scanning electron microscopy (SEM), Specific surface area (BET), Fourier infrared spectroscopy (FTIR) and X ray photoelectron spectroscopy (XPS). Experimental results showed that the optimum preparation processes for the chitosan / zeolite molecular sieve were as follows: the concentration of acetic acid was 4%, the concentration of chitosan was 7g / L, the stirring time was 10h and the stirring temperature was 30°C. And adsorption capacity of adsorption particles for ammonia and nitrate were 0.636 mg/g and 1.952 mg/g, and the removal rates were 81.60 % and 40.28 % respectively. The surface morphology of the particles showed more protrusions and micropores, the specific surface area of the particle was 391.516 m2/g. FTIR analysis showed that CH3- and NH2- have been loaded into the basic framework of zeolite molecular sieve and XPS analysis showed that the element O 1s played an important role in the attachment of chitosan to zeolite molecular sieves. Therefore, the results of the research can provide a theoretical basis for the upgrading of the water purification plants in the cold region of northern China.

Heteroatomic Zn‐MWW Zeolite Developed for Catalytic Dehydrogenation Reactions: A Combined Experimental and DFT Study

AbstractTo incorporate divalent transition metals into molecular sieve frameworks remains a great challenge in zeolite chemistry. In this study, Zn was successfully incorporated inside the MWW zeolite framework, namely Zn‐MWW (Zn−Si), through hydrothermal synthesis. A combined DFT and X‐ray absorption near edge structure (XANES) simulation was applied to unravel the location of Zn inside the structure, indicating that the most plausible Zn position is T5 with two sodium cations close to the neighboring oxygen to neutralize the charge of the zeolite. The as‐synthesized material exhibits superior catalytic performance for 1‐butene oxidative dehydrogenation with CO2 compared with MCM‐22 and ITQ‐1 supported ZnO. The 1,3‐butadiene (BD) selectivity is doubled at similar 1‐butene conversions. On the other hand, more than 51 % acetaldehyde is produced during ethanol conversion on the Zn‐MWW zeolite, whereas MCM‐22 mainly gives ethylene. The remarkable performance is associated with the efficient combination of acidity and redox properties owing to the successful insertion of atomic Zn inside the MWW framework, as demonstrated by XRD, FTIR, 29Si MAS NMR, XANES analysis, and DFT simulations.

Influence of Aluminum Addition in the Framework of MCM-41 Mesoporous Molecular Sieve Synthesized by Non-Hydrothermal Method in an Alkali-Free System

Purely siliceous MCM-41 and Al-containing MCM-41 (Al-MCM-41) mesoporous materials were synthesized by non-hydrothermal method in alkali-free ions medium at room temperature and short reaction times. Under these synthesis conditions, it was also investigated the influence of Al incorporation in the crystal structure of MCM-41. The solids were characterized by ICP-OES, AAS, N2 adsorption at 77 K, XRD, TEM, NH3-TPD, 27Al and 29Si-MAS-NMR, FT-IR and TGA. The resulting mesoporous materials showed a well-defined hexagonally ordered pore geometry maintaining a uniform and unimodal pore size distribution with high specific surface areas (1000-1400 m2g-1). The Al+3 ions were introduced successfully in the structure of the purely siliceous MCM-41 expanding the unit cell parameter and forming four-coordinated Al species, and in a less extent, forming six-coordinated Al species. In addition, the surface acidity of the MCM-41 increased with Al loading. Contrary, the presence of Al in the MCM-41 mesoporous structure resulted in a decrease of the crystallinity and specific surface area possibly due to the presence of Al species in highly distorted tetrahedral structures and Al extra-framework or amorphous alumina occluded in the pores. The MCM-41 type mesoporous materials obtained in this work show similar characteristics of those synthesized by conventional hydrothermal methods.

Catalytic performance of CeAPSO-34 molecular sieve with various cerium content for methanol conversion to olefin

A series of CeAPSO-34s with various cerium contents was synthesized and characterized by multiple techniques such as XRD, SEM, BET, 29Si MAS NMR, NH3-TPD and CO2-TPD. NH3-TPD spectra showed that a number of acid sites, especially those of strong acidity, is reduced with the increasing of Ce incorporation. Incorporation of metal ions gave rise to more silica-islands in the CeAPSO-34 framework. CO2-TPD showed that basic sites on the surface of modified samples are due to the presence of Ce-containing species incorporation into the framework of CeAPSO-34 molecular sieves. The performance of the catalysts was studied in methanol to olefin reactions at 425 °C under the atmospheric pressure. The results showed that the incorporation of cerium ions had great effects on the structure and acidity of the molecular sieves. All SAPO-34 and MeAPSO-34 molecular sieves were the very active and selective catalyst for light olefins production. Cerium incorporation improved the catalyst lifetime and favored the ethylene and propylene generation. However, an excess Ce content resulted in an inferior catalytic performance and stability. Therefore, there existed optimal cerium content for a specific SAPO-34.

High-efficiency non-thermal plasma-catalysis of cobalt incorporated mesoporous MCM-41 for toluene removal

The destruction of low concentrations of toluene in air streams using a non-thermal plasma catalysis system has been investigated in this study. A series of highly active cobalt incorporated MCM-41 (Co-MCM-41) catalysts were synthesized by a hydrothermal method. For comparison, cobalt-impregnated MCM-41 (Co-MCM-41_imp) catalysts were prepared via an impregnation method. The synthesized samples were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, UV–vis diffuse reflection spectrum (UV–vis DRS), H2-temperature-programmed reduction analyses (H2-TPR) and transmission electron microscopy (TEM). The results showed that the cobalt modified samples retained the highly ordered mesopore structure of MCM-41. In addition, the cobalt species on Co-MCM-41 was highly dispersed in the silica framework of MCM-41 molecular sieves, while the cobalt on Co-MCM-41_imp was present as cobalt oxide clusters or Co3O4 nano-particles on the external surface of MCM-41. The non-thermal plasma catalytic performance of the catalysts was evaluated by toluene oxidation using a dielectric barrier discharge (DBD) reactor. The results showed that the Co-MCM-41 exhibited better catalytic activity and stability than Co-MCM-41_imp. The main reason for the enhanced catalytic performance and stability was attributed to the well dispersion of cobalt species, good ozone decomposition activities and the high ability to degrade organic intermediates on catalyst surface.

In Situ Electrochemical Synthesis of Oriented and Defect-Free AEL Molecular-Sieve Films Using Ionic Liquids.

Simply preparing oriented and defect-free molecular-sieve films have been a long-standing challenge both in academia and industry. Most of the early works focus on the careful and multiple controls of the seeds layer or synthesis conditions. Herein, we report a one-step in situ electrochemical ionothermal method that combines a controllable electric field with ionic liquids. We demonstrate that an in-plane oriented and defect-free AEL (one molecular-sieve framework type) molecular-sieve film was obtained using an Al electrode as the Al source. The excellent corrosion-resistant performance of the film makes this technology promising in multiple applications, such as anti-corrosion coatings.

In Situ Electrochemical Synthesis of Oriented and Defect-Free AEL Molecular-Sieve Films Using Ionic Liquids

Simply preparing oriented and defect-free molecular-sieve films have been a long-standing challenge both in academia and industry. Most of the early works focus on the careful and multiple controls of the seeds layer or synthesis conditions. Herein, we report a one-step in situ electrochemical ionothermal method that combines a controllable electric field with ionic liquids. We demonstrate that an in-plane oriented and defect-free AEL (one molecular-sieve framework type) molecular-sieve film was obtained using an Al electrode as the Al source. The excellent corrosion-resistant performance of the film makes this technology promising in multiple applications, such as anti-corrosion coatings.