Molecular Sieve Research Articles

The Synergistic Effect of Pore Architect and Reducibility in Ceria-Promoted Ni Molecular Sieve for Methane Dry Reforming

Methane and carbon dioxide, the primary contributors to global warming, are now at critical levels, threatening the extinction of numerous organisms on our planet. In this regard, dry reforming of methane reactions have gained considerable attention because of the conversion capacity of CH4 and CO2 into synthetic/energy-important syngas (H2 and CO). Herein, a molecular sieve (CBV3024E; SiO2/Al2O3 = 30) with ZSM-8-type pore architect, is utilized as the support for the active site of Ni and Ce promoters. Catalysts are characterized by surface area and porosity, X-ray diffraction study, Raman and infrared spectroscopy, thermogravimetry analysis, and temperature-programmed reduction/desorption techniques. A total of 2 wt.% ceria is added over 5Ni/CBV3024E to induce the optimum connectivity of aluminum in the silicate framework. NiO residing in these porous cages are mostly under “prominent interaction with support” which is reduced easily into metallic Ni as the active sites for DRM reactions. The active sites over 5Ni2Ce/CBV3024E remain stable during the DRM reaction and achieve ~58% H2 yield after 300 min TOS at 42,000 mL/(gcat.h) GHSV and ~70% H2 yield after 20 h at 26,000 mL/(gcat.h) GHSV. The high activity after a longer time stream justifies using CBV3024E molecular sieves as the support and ceria as the promoter for Ni-based catalyst towards the DRM reaction.

Dynamics of water, CO2, ethane and their mixtures in ZSM-22 zeolite: the role of polarity and hydrogen bonding

Abstract Understanding the interplay between confinement effects and intermolecular interactions is essential for predicting molecular diffusion in zeolites. In this study, we investigate the diffusion behavior of ethane, CO2, and water in ZSM-22 molecular sieves, focusing on the effects of mixing these fluids. Our results reveal that while CO2 has minimal impact on ethane diffusion, water significantly slows ethane’s motion by forming molecular bridges across the pore structure, reducing ethane’s diffusion by up to 30%. Ethane, in turn, restricts water’s mobility, and reduces the water–water coordination number from 2.22 to 0.73 depending on concentration. The diffusion of CO2 in mixtures shows a 40% increase in pure state under confinement. The role of polarity and hydrogen bonding is crucial, with water molecules exhibiting 1.2 hydrogen bonds in the confined state—much lower than the 3.4 bonds in bulk water. Molecular rotation in ZSM-22 of all fluids occurs at two distinct time scales: the short-time fast rotation dominated by molecular inertia and the long-time rotation hindered by fluid-zeolite interactions. For water, hydrogen bonding further restricts full rotational freedom. These findings provide a comprehensive understanding of how ethane, water, and CO2 interact and diffuse in nanoporous materials.

Study on the Preparation and Structural Properties of Core–Shell Hierarchical Pore Molecular Sieve Synthesized by a Silicon Coating Method

Study on the Preparation and Structural Properties of Core–Shell Hierarchical Pore Molecular Sieve Synthesized by a Silicon Coating Method

NMR Relaxation to Probe Zeolites: Mobility of Adsorbed Molecules, Surface Acidity, Pore Size Distribution and Connectivity.

Unique structural and chemical properties, such as ion exchange, developed inner surface, etc., as well as the wide possibilities and flexibility of regulating these properties, cause a keen interest in zeolites. They are widely used in industry as molecular sieves, ion exchangers and catalysts. Current trends in the development of zeolite-based catalysts include the adaptation of their cationic composition, acidity and porosity for a specific catalytic process. Recent studies have shown that mesoporosity is beneficial to the rational design of catalysts with controlled product selectivity and an improved catalyst lifetime due to its efficient mass-transport properties. Nuclear magnetic resonance (NMR) has proven to be a reliable method for studying zeolites. Solid-state NMR spectroscopy allows for the quantification of both Lewis and Brønsted acidity in zeolite catalysts and, nowadays, 27Al and 29Si magic angle spinning NMR spectroscopy has become firmly established in the set of approved methods for characterizing zeolites. The use of probe molecules opens up the possibility for the indirect measurement of the characteristics of acid sites. NMR relaxation is less common, although it is especially informative and enlightening for studying the mobility of guest molecules in the porous matrix. Moreover, the NMR relaxation of guest molecules and NMR cryoporometry can quantify pore size distribution on a broader scale (compared to traditional methods), which is especially important for systems with complex pore organization. Over the last few years, there has been a growing interest in the use of 2D NMR relaxation techniques to probe porous catalysts, such as 2D T1-T2 correlation to study the acidity of the surface of catalysts and 2D T2-T2 exchange to study pore connectivity. This contribution provides a comprehensive review of various NMR relaxation techniques for studying porous media and recent results of their applications in probing micro- and mesoporous zeolites, mainly focused on the mobility of adsorbed molecules, the acidity of the zeolite surface and the pore size distribution and connectivity of zeolites with hierarchical porosity.

Design of Silica-Cobalt Composite Microporous Structures with Dispersed Carbon Particles for Highly Permselective Gas Separation Membranes.

Metal-doped silica membranes, fabricated via the sol-gel technique using metal nitrates, hold promise for high-temperature separation processes, such as H2 separation in steam reforming reactions. However, controlling the status of the doped metal is challenging and often leads to defect formation owing to the aggregation of metal oxides. In this study, we designed a uniform carbon-Co-SiO2 ceramic membrane using a one-pot sol-gel method with copolymerization, employing tetraethoxysilane and cobalt acetylacetone(III) (Co-(acac)3) as precursors. Organic chelate ligands within the amorphous silica network formed by the polymerization reaction were carbonized by calcination at 250-750 °C in an inert atmosphere. This approach suppressed defect formation and tailored the microporous structures to a wide range of separation systems. For example, the SiO2-Co-(acac)3 membrane calcined at 550 °C demonstrated a notable C3H6 permeance of 4.0 × 10-8 mol m-2 s-1 Pa-1 (GPU: 120), with a high C3H6/C3H8 selectivity of 46, attributed to the molecular sieving effect, whereas the membrane calcined at 650 °C exhibited a remarkable He permeance of 4.6 × 10-7 mol m-2 s-1 Pa-1 (GPU: 1400), with a high He/CH4 selectivity of 830. This study provides valuable insights into the development of defect-free carbon-cation-SiO2 ceramic membranes for a broad range of gas separation processes.

Non‐selective Defect Minimization towards Highly Efficient Metal‐Organic Framework Membranes for Gas Separation

The persistence of defects in polycrystalline membranes poses a substantial obstacle to reaching the theoretical molecular sieving separation and scaling up production. The low membrane selectivity in most reported literature is largely due to the unavoidable non‐selective defects during synthesis, leading to a mismatch between the well‐defined pore structure of polycrystalline molecular sieve materials. This paper presents a novel approach for minimizing non‐selective defects in metal‐organic framework (MOF) membranes by a constricted crystal growth strategy in a confined environment. The in‐situ ZIF formation using the densely packed seeding array between the substrate and the pre‐grown top ZIF layer yields a confined membrane interlayer, which is highly uniform with a tightly packed crystalline structure. Unlike uncontrolled crystal growth, we purposely regulate the interlayer membrane growth in the direction parallel to the substrate. A notable 99% decrease in defects in the confined interlayer was achieved compared to the random‐grown top layer, leading to a ~353% increment in H2/N2 selectivity over the non‐confined reference MOF membrane. The performance of this new membrane sits in the optimal range above the Robeson upper bound. The membrane boasts a balanced high H2 permeability (>5000 Barrer) and selectivity (>50), significantly surpassing peer ZIF membranes.

Asymmetric Pore Windows in Pillar-Layered Metal-Organic Framework Membranes for H2/CO2 Separation.

In this study, a novel ultramicroporous pillar-layered Ni-LAP-NH2 [Ni2(l-asp)2(Pz-NH2)] (l-asp = l-aspartic acid, Pz-NH2 = aminopyrazine) membranes on porous α-Al2O3 tubes with high performance and good thermal stability was first fabricated using isostructural Ni-LAP[Ni2(l-asp)2(Pz)] (Pz = pyrazine) crystals as seeds. Utilizing the principle of reticular chemistry, here, we introduced the active amino side group into the Ni-LAP frameworks by replacing the pillar-layered ligand Pz with Pz -NH2 while maintaining the original Ni-LAP small pore size, and the amino side group induced a "steric hindrance" effect and the physical adsorption affinity, which synergistically delayed CO2 penetration. It was found that the preferential (111) orientation Ni-LAP-NH2 membrane (Z10) exhibited a high H2/CO2 separation performance with a separation factor of 41.7 and H2 permeance of 9.08 × 10-8 mol·m-2·s-1·Pa-1 under optimal conditions. These MOF materials demonstrated potential for industrial H2 purification due to their tunable pore structure and remarkable stability. Moreover, this strategy offers an effective approach to tailoring pillar-layered MOF membranes with targeted molecular sieving ability.

Pore configuration control in hybrid azolate ultra-microporous frameworks for sieving propylene from propane.

Developing porous adsorbents for the complete sieving of propylene/propane mixtures represents an alternative method to energy-intensive cryogenic distillation processes. However, the similar physical properties of these molecules and the inherent trade-off among adsorption capacity, selectivity, diffusion kinetic and host-guest binding interactions in molecular sieving adsorbents makes their separation challenging. Here we report the separation of propylene/propane mixtures through a crystalline porous material (HAF-1) that features channels and shrinkage throats-the latter defined as narrower channels that connect the main channels and a molecular pocket-where the throat aperture is between the kinetic diameters of propylene and propane. Single-crystal X-ray diffraction and computational simulation reveal that the shrinkage channels and hanging molecular pockets are key to ensure high sieving efficiency and high propylene adsorption capacity. Dynamic breakthrough experiments show that HAF-1 enables the achievement of high-purity (≥99.7%) propylene with a productivity of 33.9 l kg-1 by just one adsorption-desorption circle from propylene/propane mixtures.

Carbon Molecular Sieve Membranes from Poly(oxo-biphenylene-isatin) with Increasingly Bulky Fluorine Substitution: Characterization and Gas Transport Properties

Carbon Molecular Sieve Membranes from Poly(oxo-biphenylene-isatin) with Increasingly Bulky Fluorine Substitution: Characterization and Gas Transport Properties

Supramolecular Interfacial Assembly: Integrating Supramolecular Hosts into Polymeric Membranes through an Aqueous Interface

AbstractEfficient incorporation of macrocycles in polymeric membranes can impart the overall matrix with new properties for a range of cutting‐edge applications. Here, we introduce a Supramolecular Interfacial Assembly (SIA) method for the fabrication of polymeric membranes featuring embedded macrocycles. Through harnessing the quasi‐liquid nature of the concentrated polymer solution, SIA orchestrates the homogeneous spreading of macrocycles in an aqueous layer on its surface, leading to the creation of an interface between “water/water” phases, subsequently forming a cross‐linked membrane driven by supramolecular electrostatic interactions. Remarkably, compared to the traditional interfacial polymerization, SIA adheres to a “green” paradigm without the need for organic solvents. The resultant composite membrane exhibits superior performance in organic solvent nanofiltration (OSN), owing to the precise molecular sieving property provided by the macrocycles with well‐defined permanent cavities. This fabrication method holds great promise for the innovative design and production of composite membranes that seamlessly integrates macrocycles with conventional polymers, which can greatly impact the design and preparation of advanced membrane materials in the future.

Functional Immunoaffinity 3D Magnetic Core-Shell Nanometallic Structure for High-Efficiency Separation and Label-Free SERS Detection of Exosomes.

Tumor exosomes, known as maternal cell messengers, play an important role in cancer occurrence, proliferation, metastasis, immune escape, drug resistance, and other processes and are an entry point for cancer research. However, there is still a lack of an efficient detection technology for exosomes. In this study, the ultrahigh sensitivity SERS nanoprobe with a three dimensional (3D) magnetic core/Au nanocolumn/Au nanoparticles shell strongly coupling multistage structure (Fe3O4@NR-NPs) was constructed by crystal growth of nanocrystals in the confined space of a central radiating single particle mesoporous molecular sieve channel and strong coupling secondary growth of gold particles. The exosomes were confined onto the "hot spot" of plasmonic nanoparticles and rapidly enriched by CD63 antibody functional-Fe3O4@NR-NPs to achieve high sensitivity detection, with the limit of detection of 1 × 103 particles/mL (S/N = 3). The spectral data set of different exosomes is applied to train for multivariate classification of cell types and to estimate how the normal exosome data resemble cancer cell exosomes by principal component analysis (PCA). Finally, this detection method has also been successfully employed for the detection of exosomes in complex samples; this proves that the proposed SERS-based method is a promising tool for clinical cancer screening.

Supramolecular Interfacial Assembly: Integrating Supramolecular Hosts into Polymeric Membranes through an Aqueous Interface.

Efficient incorporation of macrocycles in polymeric membranes can impart the overall matrix with new properties for a range of cutting-edge applications. Here, we introduce a Supramolecular Interfacial Assembly (SIA) method for the fabrication of polymeric membranes featuring embedded macrocycles. Through harnessing the quasi-liquid nature of the concentrated polymer solution, SIA orchestrates the homogeneous spreading of macrocycles in an aqueous layer on its surface, leading to the creation of an interface between "water/water" phases, subsequently forming a cross-linked membrane driven by supramolecular electrostatic interactions. Remarkably, compared to the traditional interfacial polymerization, SIA adheres to a "green" paradigm without the need for organic solvents. The resultant composite membrane exhibits superior performance in organic solvent nanofiltration (OSN), owing to the precise molecular sieving property provided by the macrocycles with well-defined permanent cavities. This fabrication method holds great promise for the innovative design and production of composite membranes that seamlessly integrates macrocycles with conventional polymers, which can greatly impact the design and preparation of advanced membrane materials in the future.

Performance enhancement using novel hybrid rotary desiccant wheels having non-homogeneous mixture of multiple desiccant layers

Comfortability of human beings is increasing day by day which leads the researchers to look for various innovative potential solutions in the air conditioning system. The desiccant cooling system is one of the emerging areas which is efficient and environment friendly. This study presents a comprehensive analysis of the adsorption/desorption characteristics of hybrid rotary desiccant wheels along with conventional silica gel (SG) and molecular sieves (MS) wheels. A hybrid rotary desiccant wheel is having non-homogeneous mixture of multiple desiccant types (different combinations of conventional SG and MS). Governing equations are solved iteratively by finite volume method (FVM) and the computer model was developed using FORTRAN 95. The effect of a mixture of desiccant materials over moisture removal rate, efficiency, dehumidification coefficient of performance (DCOP) of the wheel, and process air outlet temperature is studied. The influence of various parameters, such as regeneration air temperature (of 60–120 °C) and entry length (0.1 m and 0.2 m) on the aforementioned factors are also analysed. The optimum performance was achieved in the SG wheel and MS wheel at lower and higher regeneration temperatures, respectively. Thus, a trade-off is carried out to get the optimum combination of both SG and MS desiccant concentration for better performance. The numerical results of these hybrid rotary desiccant wheels showed that the performance of the wheel can be enhanced by 4.8–62.8% using this innovative design.

Research on the modification technology of beta molecular sieve

The influence of temperature and time of the acid washing and hydrothermal treatment on Beta zeolite properties was examined in detail, the results revealed that acid washing at 2h and 80℃and 2h hydrothermal treatment at 650℃are the best modification operating conditions. The different SiO2/Al2O3ratio of Beta zeolite are systematically modified using optimized modification operating conditions. Beta zeolite modified from higher SiO2/Al2O3ratio of the starting Beta also has higher SiO2/Al2O3 ratio. Crystallinity of starting Beta zeolite has less effect on the modified Beta zeolite. As the SiO2/Al2O3 ratio of starting Beta increased, total acid amount of modified Beta decreased. When the SiO2/Al2O3 ratio of starting Beta is bigger, the surface area and pore volume is higher.

Solvent‐free synthesis of medium chain triacylglycerols by esterification of capric, caprylic acids with 1, 3‐specific and non‐specific lipases

AbstractMedium chain triacylglycerols (MCTs) are used as a functional oil in various food and pharmaceutical formulations because of their numerous health benefits and physical properties. Enzymatic esterification of glycerol with caprylic (C8:0) and capric acids (C10:0) in a molar ratio of 1:3.5 [50% (C8:0) and 50% (C10:0)] was carried out for the solvent free synthesis of MCTs using 5% (w/w) 1,3 specific lipase, Lipozyme RM IM and non‐specific lipase, Novozym 435 in the presence of molecular sieves (10%) and low pressure conditions (50 and 150 mbar) at 50°C. Novozym 435 was more effective in the esterification reaction under 50 mbar reduced pressure, achieving ~54.74% triacylglycerol formation in 6 h, compared to Lipozyme RMIM, which achieved ~31.25% under the same conditions. Further reactions with Novozym 435 for 24 h showed that the maximum formation of MCTs occurred at 20 h (86.46 ± 3%), after which the reaction reached equilibrium. When 50 mbar was used, the formation of triacylglycerols enhanced 13 times compared with the results obtained at atmospheric pressure condition. Chemical characterization of the final MCTs confirmed the formation of four triacylglycerol species (TAG (8:0/8:0/8:0), TAG (8:0/8:0/10:0), TAG (8:0/10:0/10:0), and TAG (10:0/10:0/10:0) with LC–MS and NMR analysis. The melting and crystallization points of the synthesized oil was found to be −3.47°C and −23.48°C, respectively. Our findings contribute to developing a green process for synthesizing MCTs using two different fatty acids. The final product can be used as a nutraceutical oil or as an ingredient to enhance the food's physical properties.

Nano-lamellar H-ZSM-5 molecular sieves for enhanced indoor air purification: Synthesis and adsorption characterization.

The rapid growth of cities has been accompanied by problems with urban air quality, making air pollution challenging to manage. In this situation, people focus on indoor building materials to improve air quality. In this paper, a novel bola-type surfactant was synthesized and used as a template, using ethyl orthosilicate and sodium meta-aluminate as the silicon and aluminum source, in the ratio of n(NaOH): n(NaAIO2): n(SiO2): n(SDA): n(H2O) as 30:2.5:120:5:4800. Hydrothermal preparation of ZSM-5 molecular sieves with a nanosheet structure (H-ZSM-5) was accomplished. The manufactured lamellar ZSM-5 molecular sieves were examined using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and adsorption and desorption techniques. Traditional microporous ZSM-5 had a considerably lower static adsorption of formaldehyde molecules. The findings demonstrated that the nano-lamellar H-ZSM-5 molecular sieve can purify and eliminate larger molecular VOCs inside because it has the ability to adsorb larger molecular diameter VOCs. Additionally, the effectiveness of the adsorption was assessed using toluene vapour molecules with higher molecular diameters. The findings demonstrate that the nanosheet H-ZSM-5 molecular sieve can remove bigger molecule VOCs from indoor air and can be utilised to purify indoor spaces. This study offers a fresh approach to indoor environmental cleanup by demonstrating the capability of nano-lamellar H-ZSM-5 molecular sieves for molecular adsorption.

Gas adsorption and separation applications of MOF materials

Abstract. Low-carbon hydrocarbons (C1-C4) are really important raw materials used in making different kinds of big molecules and stuff in industries. Before, people mostly used super cold cooling and a method where stuff gets soaked up. But these ways need big machines and use a lot of energy. So, scientists are trying to make new ways to separate things that don't use as much energy. One great idea is using how different gases stick to things to separate them. This idea could be a brilliant way to replace the old methods. The most important part of this idea is making things that can stick to the gases. There's this special material called metal-organic frameworks (MOFs) that's a mix of things from nature and chemicals. It has tiny holes and places that can do special things, and it's being studied a lot for separating gases. Traditional porous materials like activated carbon, silica gel, and molecular sieves have been widely used in industries, which has greatly contributed to industrial growth and people's living standards. MOFs have changeable structures and spots that can do special things. By changing the metal bits or the organic parts, we can control the size of the holes in MOFs, the special spots, and how much surface they have. These things make MOFs useful for storing gases, separating stuff by sticking and making reactions happen in fields like chemistry [1-3]. This paper explores the categories of MOF applications.

Organic Solvent Nanofiltration Membrane with In Situ Constructed Covalent Organic Frameworks as Separation Layer.

Organic solvent nanofiltration (OSN) technology is advantageous for separating mixtures of organic solutions owing to its low energy consumption and environmental friendliness. Covalent organic frameworks (COFs) are good candidates for enhancing the efficiency of solvent transport and ensuring precise molecular sieving of OSN membranes. In this study, p-phenylenediamine (Pa) and 1,3,5-trimethoxybenzene (Tp) are used to construct, in situ, a TpPa COF skin layer via interfacial polymerization (IP) on a polyimide substrate surface. After subsequent crosslinking and activation steps, a kind of TpPa/polyimide (PI) OSN membrane is obtained. Under optimized fabrications, this OSN membrane exhibits an ethanol permeance of 58.0 LMH/MPa, a fast green FCF (FGF) rejection of 96.2%, as well as a pure n-hexane permeance of 102.0 LMH/MPa. Furthermore, the TpPa/PI OSN membrane exhibits good solvent resistance, which makes it suitable for the separation, purification, and concentration of organic solvents.

Shape‐Selective Zeolites for Tandem CO2 Hydrogenation‐Carbonylation Reactions

The valorization of carbon dioxide as a C1 building block in C‐C bond forming reactions is a critical link on the road to carbon‐circular chemistry. Activation of this inert molecule through reduction with H2 to carbon monoxide in the reverse water‐gas shift (RWGS) reaction can be followed by a wide spectrum of consecutive carbonylation reactions, but the RWGS is severely equilibrium limited at the moderate temperatures of carbonylations. Here we successfully reconcile both reactions in one pot, while avoiding incompatibilities through a zeolite‐based compartmentalized approach. More specifically, Pt encapsulated in a small‐pore LTA zeolite selectively generates carbon monoxide in mild reaction conditions; an ensuing one‐pot carbonylation reaction allows to shift the equilibrium through continuous consumption of CO. Moreover, the zeolite encapsulation avoids undesired reactions like hydrogenation of the olefin reactant through a molecular sieving effect. This strategy was first studied in‐depth for Rh‐catalyzed olefin hydroformylation with CO2/H2, affording aldehydes in good yields with high regioselectivities. The methodology was then extended to a variety of carbonylations using CO2 for the synthesis of bulk and fine chemicals.

Shape-Selective Zeolites for Tandem CO2 Hydrogenation-Carbonylation Reactions.

The valorization of carbon dioxide as a C1 building block in C-C bond forming reactions is a critical link on the road to carbon-circular chemistry. Activation of this inert molecule through reduction with H2 to carbon monoxide in the reverse water-gas shift (RWGS) reaction can be followed by a wide spectrum of consecutive carbonylation reactions, but the RWGS is severely equilibrium limited at the moderate temperatures of carbonylations. Here we successfully reconcile both reactions in one pot, while avoiding incompatibilities through a zeolite-based compartmentalized approach. More specifically, Pt encapsulated in a small-pore LTA zeolite selectively generates carbon monoxide in mild reaction conditions; an ensuing one-pot carbonylation reaction allows to shift the equilibrium through continuous consumption of CO. Moreover, the zeolite encapsulation avoids undesired reactions like hydrogenation of the olefin reactant through a molecular sieving effect. This strategy was first studied in-depth for Rh-catalyzed olefin hydroformylation with CO2/H2, affording aldehydes in good yields with high regioselectivities. The methodology was then extended to a variety of carbonylations using CO2 for the synthesis of bulk and fine chemicals.