Pore Molecular Sieves Research Articles

Dynamic breakthrough performance of low concentration CO2 adsorption in fixed-bed column with porous amino acid ionic liquid composites

Low concentration carbon dioxide (CO2) capture from air or confined spaces currently faces significant challenges, such as relatively poor dynamic adsorption breakthrough performance and cyclic stability. In our previous work, functionalized ionic liquid (IL) tetraethylammonium glycine ([N2222][Gly]) and porous molecular sieve (SBA-15) were combined to synthesize porous amino acid IL composite 60 wt% [N2222][Gly]@SBA-15 with microporous and ultra-microporous structures, which provide a new pathway for low concentration CO2 capture. In order to further obtain the dynamic CO2 adsorption breakthrough performance of this material under simulated actual working conditions, the effects of temperatures, relative humidity (RH) and CO2 concentrations on CO2 adsorption and desorption breakthrough performance of 60 wt% [N2222][Gly]@SBA-15 in a fixed-bed column were systematically studied in this work. The results indicated that CO2 adsorption capacity is up to 1.81 mmolCO2/g-adsorbent at 298.15 K, 1 bar and 0 % RH under 1 vol% CO2-containing gas mixture balanced with N2 and reaches 2.44 mmolCO2/g-adsorbent at 15 % RH due to the mechanism change of CO2 reaction with primary amine from 2: 1 under dry gas to 1: 1 stoichiometry in the presence of moisture. Moreover, the adsorbent maintains good cyclic adsorption-desorption performance. Further, CO2 adsorption breakthrough behaviors were well fitted by Avrami kinetic model, and the CO2 adsorption rate of 60 wt% [N2222][Gly]@SBA-15 was controlled by intra-particle diffusion. This work implied that IL-modified adsorbents have great potentials for low concentration CO2 capture applications.

Performance evaluation of carbon-negative syngas production via chemical looping reforming of methane from biomass pyrolysis volatiles

To realize the clean and efficient directional conversion of biomass, chemical looping reforming of biomass volatile CH4 based on a decoupling strategy is expected to carry out carbon-negative production of hydrogen-rich syngas. In this paper, a multi-functional oxygen carrier (NiFe2O4@SBA-16) for encapsulating the active metal oxide component NiFe2O4 with a three-dimensional interconnecting pore molecular sieve SBA-16 was designed. The experimental results showed that the modification strategy of composite metal oxide encapsulation improved syngas selectivity and CH4 conversion based on the fixed-bed reactor. 20 %NiFe2O4@SBA-16 showed 22.1 % CH4 conversion and 92.6 % CO selectivity under 750 °C, and it maintained good cycle stability after 15 cycles. The H2/CO ratio was effectively improved by adding part of CO2 into the feed gas, and the CH4 conversion reached over 35 %. This study provides essential data for the clean preparation of hydrogen-rich syngas from biomass and the development and design of multifunctional oxygen carriers.

Enhanced electrocatalytic properties in dye-sensitized solar cell via Pt/SBA-15 composite with optimized Pt constituent

The Low utilization and high cost of platinum counter electrode (CE) in the application of dye-sensitized solar cells has limited its large-scale manufacturing in the industry. Herein, a facile pyrolysis combination of Pt and SBA-15 molecular sieve (MS) formed 1.6–1.9 times higher amount and 2–3 times reduced dimension of Pt distributed within porous structure of SBA-15. The composite CE with 20 % of SBA-15 exhibited an enhanced power conversion efficiency of 9.31 %, exceeding that of absolute Pt CE (7.57 %). This superior performance owed to the promoted oxidation-reduction rate of I3−/I− pairs at the CE interface and the increased conductivity of CE materials attributed from well distributed Pt particles. This work has demonstrated the significance of utilizing porous molecular sieves for dispersing catalytic sites when designing a novel type of counter electrode and their application in DSSCs.

Synthesis and mechanism of porous molecular sieves

Porous molecular sieve was a kind of material with different pore structure. Porous molecular sieve had molecular sieve separation ability and rapid mass transfer ability. These materials effectively solved the mass transmission problem of traditional molecular sieve. And allowed substrate molecules to enter the active site located in the micropore, thus improving the reaction rate and lifetime. In addition, the secondary porosity of the porous zeolite created an ideal space for the deposition of the products, controlling their size and allowing high dispersion and strong interactions between the zeolite and the medium. In this paper, the synthesis and mechanism of porous molecular sieve were summarized and summarized, which laid a theoretical foundation for the synthesis of porous molecular sieve.

Effects of a Cellulose Aerogel Template on the Preparation and Adsorption Properties of Coal Gangue-Based Multistage Porous ZSM-5.

In this study, a ZSM-5/CLCA molecular sieve was prepared by the hydrothermal method using coal gangue as the raw material and cellulose aerogel (CLCA) as the green templating agent, which not only reduces the cost of traditional molecular preparation but also improves the comprehensive resource utilization rate of coal gangue. Through a series of characterization methods (XRD, SEM, FT-IR, TEM, TG, and BET), the crystal form, morphology, and specific surface area of the prepared sample were tested and analyzed. The performance of the adsorption process of malachite green (MG) solution was analyzed by adsorption kinetics and adsorption isotherm. The results show that the synthesized zeolite molecular sieve and the commercial zeolite molecular sieve are highly consistent. At a crystallization time of 16 h, a crystallization temperature of 180 °C, and an additive amount of cellulose aerogel of 0.6 g, the adsorption capacity of ZSM-5/CLCA for MG was up to 136.5 mg/g, much higher than that of commercially available ZSM-5. This provides an idea for the green preparation of gangue-based zeolite molecular sieves to remove organic pollutants from water. Moreover, the process of adsorbing MG on the multistage porous molecular sieve, which is spontaneous, conforms to the pseudo-second-order kinetic equation and Langmuir isothermal adsorption model.

Porous multi-site ionic liquid composites for superior selective and reversible adsorption of ammonia

Ionic liquids (ILs) with low vapor pressure, tunable structures and good NH3 affinity provide an inspiring way to efficiently capture NH3. However, the high viscosity of most ILs limited mass transfer, which incumbers their industrial applications. Besides, how to simultaneously achieve high selectivity, capacity and reversibility of NH3 still face great challenge. Herein, four novel hydroxyl ammonium protic ILs (HAPILs), including methyldiethanolammonium trifluoromethanesulfonate ([MDEAH][CF3SO3]), triethanolammonium trifluoromethanesulfonate ([TEAH][CF3SO3]), dimethylethanolammonium trifluoromethanesulfonate ([DMEAH][CF3SO3]) and diethylethanolammonium trifluoromethanesulfonate ([DEEAH][CF3SO3]), with multiple hydrogen bonding donors that can interact with more over two NH3 molecules were designed and synthesized, and were further supported onto porous molecular sieves to overcome the above problem. Among the prepared porous HAPIL composites, 50 wt% [TEAH][CF3SO3]@MCM-41 showed the highest NH3/CO2 selectivity of 62 under 313 K and 0.1 MPa compared with the state-of-the-art values, along with high capacity of 114.3 mgNH3/g-adsorbent. The excellent NH3 adsorption performance was attributed to the synergistic interaction of mesoporous effect and multiple hydrogen bonding between NH3 and HAPILs. Furthermore, the porous HAPIL composites exhibited great recyclability after six cycles, revealing great potentials in industrial application of efficient and reversible NH3 separation.

Porous molecular sieve polymer composite with high CO2 adsorption efficiency and hydrophobicity

Greenhouse gases lead to frequent natural disasters, and CO2 emissions from flue gases account for nearly half of anthropogenic CO2 emissions. As an adsorbent, molecular sieves show excellent CO2 adsorption; however, their defects limit their industrial application. To solve the problem of powder blockage and H2O absorption, we proposed the in-situ growth of molecular sieve in polyacrylate matrix beads to obtain molecular sieve composite for CO2 capture in flue gas after combustion. Compared with those of pristine NaY, the CO2 adsorption capacity of NaY@PA composite increased by 17.9 % and the H2O adsorption capacity decreased by 36.6 %. For further reduction in H2O absorption, post-modified composite NaY-ZIF@PA was synthesized by loading ZIF on NaY@PA surface to form a bilayer composite structure. The H2O absorption of NaY-ZIF@PA was reduced by 54.8 %, thus ensuring highly efficient CO2 adsorption.

Superior selective adsorption of trace CO2 induced by chemical interaction and created ultra-micropores of ionic liquid composites

Effective capture of trace CO2 in atmosphere or confined spaces to ensure human beings safety draw a lot of attention, however, how to simultaneously improve CO2 capacity and selectivity still faces great challenge. Herein, combining porous molecular sieves (SBA-15 and MCM-41) and the anion-functionalized ionic liquid (IL) tetraethylammonium glycinate ([N2222][Gly]), a series of hierarchically porous IL composites with different IL loadings were designed and prepared. Compared with pristine supports, the incorporation of [N2222][Gly] simultaneously improves CO2 capacity and CO2/N2 selectivity by ordersofmagnitude, especially for confined spaces (<5000 ppm) and air (415 ppm). When the IL loading was 60 wt%, novel micropores were created, especially ultra-micropores (<0.65 nm), which are not present in bare supports and other [N2222][Gly]@SBA-15 (15, 30 and 45 wt%). Among them, 60 wt%[N2222][Gly]@SBA-15 showed the highest CO2 uptake of 1.45 and 1.88 mmolCO2/g-adsorbent at 0.0005 and 0.005 bar under 313 K along with recyclability, which are much superior to the state-of-the-art reported values. Moreover, superb ideal CO2/N2 selectivity of 11,545 at 0.005 bar and 288 K was achieved, which was 288 times that of SBA-15. Meanwhile, mixed gas breakthrough experiments demonstrated that 60 wt% [N2222][Gly]@SBA-15 shows outstanding CO2 separation performance under simulative confined spaces and ambient air. The ultra-high CO2 separation performance was attributed to the synergy of chemical interaction between the IL anion and CO2 as well as newly created micro- and ultra-micropores effect. This work provides guidelines for the design of IL composites with ultra-micropores for efficient trace CO2 removal.

Encapsulation and controlled release of isothiazolinones in zeolite NaY (FAU)

NaY zeolite, an ordered, large pore molecular sieve pertaining to the FAU zeolite structural group, was studied as a novel matrix for the efficient preparation of a supported isothiazolinone-based biocide, and the results were compared to those corresponding to mesoporous silicas. To analyze the possibility of reducing the biocide ecotoxicity by encapsulation, a commercial biocide used for latex preservation (CMIT/MIT) was incorporated in the NaY zeolite structure by using two different methodologies: equilibrium adsorption (Zeo/Bio sample) and impregnation by total wetting (Zeo/Impreg sample). In the corresponding release tests, despite the large difference in the initial biocide amount released, the shape of the curve is nearly the same for both methods. Microbiological tests against fungi and bacteria were performed. The obtained results were compared to those previously obtained using mesoporous ordered silica SBA-15 and mesoporous foam MCF matrices (mesoporous/biocide samples named SBA-15/Bio, SBA-15/Impreg and MCF/Bio and MCF/Impreg respectively). For the Staphylococcus aureus the results from agar well diffusion assay shows that the inhibition zone is about 64 mm for Zeo/Impreg and about 55 mm for Zeo/Bio. As regards all the other materials, the inhibition zone does not exceed 46 mm. In the case of Escherichia coli, Zeo/Bio and Zeo/Impreg have an inhibition zone of about 43 and 37 mm, respectively. No one of the other materials shows an inhibition zone larger than 30 mm. Zeo/Impreg showed a greater inhibition zone against fungi (47 mm versus Chaetomium globosum and 53 mm versus Alternaria alternata, respectively) than SBA-15 and MCF impregnated with biocide.

Preparation of Polypropylene Foams with Bimodal Cell Structure Using a Microporous Molecular Sieve as a Nucleating Agent

A novel approach for fabricating polypropylene (PP) foam with bimodal cellular structure utilizing CO2 as a physical foaming agent was established by adding porous molecular sieve (PMS) as nucleati...

Fluoride-free Synthesis of Germanosilicate CIT-13 and Its Inverse Sigma Transformation To Form CIT-14

Germanium-containing, extra-large pore molecular sieve CIT-13 is synthesized without the use of fluoride. After the removal of occluded organics, CIT-13 obtained from fluoride-free preparation shows significant differences from CIT-13 samples prepared in the presence of fluoride. CIT-13 prepared using a fluoride-free method is able to undergo inverse sigma transformation to yield CIT-14 and transforms into a CIT-5-type germanosilicate much faster than Ge-CIT-13 of similar Si/Ge ratios from a fluoride-containing synthesis. A Rietveld-refined structure solution for CIT-14 reveals that this new molecular sieve possesses 12- and 8-membered ring channels. Results from 19F magic-angle spinning (MAS) and 1H–29Si cross-polarized MAS nuclear magnetic resonance spectroscopy reveal that CIT-13 crystallized without fluoride has germanium siting which is different from CIT-13 synthesized in the presence of fluoride.

Research of Advanced Materials for Volatile Organic Compounds Treatment

Volatile organic compounds (VOCs) are one of the important pollutants, which are easy to cause serious harm to the environment and human body. In this paper, solid adsorbents based on carbon-based adsorbents and porous molecular sieves, organic adsorbents and chemical materials based on chemical catalysts and photocatalysts are introduced. The effects of pore structure, specific surface area and acid base functional groups on the saturated adsorption capacity of carbon based adsorbents and porous molecular sieves were discussed. The differences between volatile organic solvents and new microemulsion systems and ionic liquids in terms of volatility, solubility and selectivity were compared. The latest progress of conventional thermal catalysts (noble metals, transition metals) and Photocatalysts (Metal/Nonmetal Doping, Nanomaterial Composite, Dye Sensitization) in VOCs treatment was discussed. The application prospects of new materials around biosurfactants and ionic liquids in the treatment of volatile organic compounds were pointed out.

Oxidative Desulfurization Performance of CoAPO-5 Catalysts Synthesized by Novel Dynamic Hydrothermal Method

CoAPO-5 molecular sieves were synthesized by a novel dynamic method. Crystallization, morphology and surface acidity were investigated by XRD, SEM, and Py-IR in details, and compared with samples prepared by traditional static method. Synthesis conditions, reaction time, temperature and the amount of catalyst were optimized as important parameters. The desulfurization performance of CoAPO-5 catalysts synthesized by two different methods was evaluated and compared. Also, some experiments were carried out to test selectivity and regenerability of CoAPO-5 catalysts synthesized by the dynamic method. Finally, ODS reaction kinetics and mechanism using CoAPO-5 was studied and discussed. Results indicated that dynamic method greatly shortened crystallization time, while kept the same structure and sulfur removal capacity of CoAPO-5. The dynamic synthesis method could be considered as an alternative method to prepare porous molecular sieves.

Synthesis of a novel nano-rod-shaped hierarchical silicoaluminophosphate SAPO-11 molecular sieve with enhanced hydroisomerization of oleic acid to iso-alkanes.

In this article, a novel nano-rod-shaped SAPO-11 molecular sieve (SAPO-11-A-F) with a thickness of ca. 100 nm was successfully fabricated by the in situ seed-induced steam-assisted method using the cationic surfactant cetyltrimethylammonium bromide (CTAB) as a mesoporous template and a nonionic copolymer poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide), F127, as the crystal growth inhibitor. The fabricated nano-rod-shaped SAPO-11-A-F possessed nanocrystalline size, a hierarchical porous structure, and enhanced acidic sites. The added CTAB was mainly used to enhance the mesoporous structure and acid, and F127 acted as a grain growth inhibitor. According to the orientation growth mechanism of the molecular sieves, the crystallization mechanism of the nano-rod-shaped hierarchical porous molecular sieves with different crystallization times was investigated. It was found that the nano-rod-shaped molecular sieves were formed by the accumulation of nano-sheets. Compared to three nickel catalysts with different silicoaluminophosphate SAPO-11 molecular sieves in the hydroisomerization of oleic acid to iso-alkanes, the bifunctional catalyst of 7% Ni/SAPO-11-A-F had higher isomeric selectivity (79.8%); in particular, the isomeric octadecane showed stronger selectivity, indicating that the nano-rod-shaped SAPO-11 molecular sieve is more beneficial for the hydrodehydration reaction.

On the mechanism for ethyl transfer and removal from ethylbenzene during commercial xylene isomerization

Abstract Ethylbenzene (EB), a structural isomer of xylenes, is present in feedstocks for commercial xylene isomerization. EB cannot be economically separated from the close boiling xylenes by distillation. It must be converted to lower and/or higher boiling byproducts that can, to prevent its buildup in the xylene isomerization unit recycle loop. Several routes are available for converting EB, including ethyl transfer to another aromatic via transalkylation, and EB dealkylation. A mechanism initiated by hydride abstraction has often been cited for ethyl transfer over large pore molecular sieves, based on old data developed for liquid phase conversion over HF/BF3 catalysts which are strong Lewis acids. However, ethyl transfer occurs readily over large pore molecular sieves that contain only Bronsted acid sites, and little or no Lewis acidity via a mechanism in which the ethyl group never leaves the first ring before being transferred to a second. I propose reconsideration of an SN2 mechanism instead. Also, a published mechanism proposed for EB dealkylation/realkylation that occurs over medium pore sieves is corrected to show ethylene as a stable intermediate and expanded to provide the mechanism for EB dealkylation over catalysts comprising medium pore sieves and a mild hydrogenation catalyst. The role of dual bed catalysts that employ a combination of transition state and product shape selectivity to further reduce xylene loss is explained.

Fluoride Removal by Adsorption Using Micro Porous Molecular Sieves (4a0)

Fluoride Removal by Adsorption Using Micro Porous Molecular Sieves (4a0)

Cobalt impregnated porous catalyst promoting ammonium sulfate recovery in an ammonia-based desulfurization process

Oxidation of ammonium sulfite plays an important role in the ammonia-based wet flue gas desulfurization. In this work, a porous molecular sieve (4A type) supported cobalt catalyst, named as Co-MS-4A, was developed to expedite the oxidation of ammonium sulfite. The experimental results revealed that the oxidation rate was increased by 1.7 to 6.0 times in comparison with the uncatalyzed scenario. The Co-MS-4A catalyst with a nominal Co loading of 1.2wt% exhibited the highest oxidation rate of (NH4)2SO3 among the tested catalysts. It was characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and Energy Dispersive Spectrometer (EDS). The BET data showed that the support retained its mesoporous structure after the cobalt impregnation. Due to the low cobalt loading in the catalyst, no obvious Co diffraction peaks was observed by the XRD. The presence of the cobalt species including Co2+ and Co3+ in the catalyst was confirmed as depicted by the XPS spectra. The TEM-EDS spectra indicated that cobalt particles distributed uniformly in the tunnels of MS-4A support. Furthermore, the effects of operation parameters, such as ammonium sulfite concentration, catalyst concentration, pH, oxygen partial pressure, and temperature, on the oxidation rate of ammonium sulfite were investigated in a bubbling tank. The apparent activation energy of the ammonium sulfite oxidation catalyzed by Co-MS-4A was 17.67kJ·mol−1. The kinetic analysis implied that the catalyzed oxidation of ammonium sulfite is rapid with a Hatta number higher than ∼4.15, and that the overall reaction was controlled by the mass transfer of oxygen. The work provides a new approach for recycle of byproduct in ammonia desulfurization without transition metal consumption and pollution.

Preparation and Characterization of Hierarchical Pore Molecular Sieve with Large Pore Size

A series of hierarchical pore molecular sieves (HPMSs) with pore size up to 6.0 nm were prepared using triblock copolymer (P123) as mesoporous template agent and characterized by N2 adsorption-desorption. Cobalt-loaded catalysts were prepared by impregnating cobalt nitrate onto HPMSs and characterized by X-ray diffraction and scanning electron microscopy. The result indicates that mesopore size of HPMS increased along with the increment of the amount of P123. The selectivity of the catalysts for Fischer-Tropsch synthesis was evaluated in a fixed-bed reactor, and the results show that the selectivity of C12+ hydrocarbons is increased with the increment of the pore size.

Aerosol-assisted synthesis of hierarchical porous titanosilicate molecular sieve as catalysts for cyclohexene epoxidation

Hierarchical titanosilicate composites (HTS) have been synthesized by an aerosol spray method, by which TS-1 nanoparticles were assembled with cetyl trimethyl ammonium bromide and tetraethylorthosilicate/tetra-n-butyl titanate to form a hierarchical porous composites with a core–shell structure. The structure, porosity, morphology and composition of the materials were characterized by X-ray diffraction, nitrogen adsorption isotherm, Raman spectroscopy, electron microscopy and X-ray fluorescence spectroscopy. The hierarchical porous molecular sieve combines the advantages of TS-1 and Ti-KIT-1, and shows high activity and selectivity to epoxide in cyclohexene epoxidation with H2O2. The yield of cyclohexene oxide on HTS is much higher than those on TS-1 and Ti-KIT-1. The selectivities to cyclohexene oxide and 1,2-cyclohexanediol can be adjusted by varying the titanium contents of the HTS samples.

Heterogeneous Catalysis for the Conversion of Sugars into Polymers

The synthesis of commodity polymers from biomass presents interesting challenges and opportunities for new catalytic chemistries. Starting from glucose, reaction pathways to a variety of monomers for commodity polymers are presented. The first step for each pathway is the isomerization of glucose to fructose. This reaction can now be accomplished in aqueous media with hydrophobic, large pore molecular sieves that contain Lewis acid sites as catalysts. A typical catalyst is a pure-silica molecular sieve having the zeolite beta topology and containing a small amount of framework Sn4+ (Sn-Beta). Dehydration of fructose into 5-hydroxymethylfurfural (HMF) provides a convenient path that can lead to 2,5-furandicarboxylic acid (FDCA) for the synthesis of polyethylene furanoate (PEF) or purified terephthalic acid (PTA) (via Diels–Alder reactions) for the synthesis of polyethylene terephthalate (PET). Recent progress on the dehydration of lactic acid could open new routes to acrylic acid and acrylonitrile that are used to produce polyacrylic acid and polyacrylonitrile, respectively, provided more selective catalysts for the retro-aldol deconstruction of fructose are developed.