Silica Gel Support Research Articles

Experimental and kinetic study on the cyclic removal of low concentration CO2 by amine adsorbents in confined spaces

Amine-based adsorbents show great promise for removing low-concentration CO2 from environmental control and life support systems (ECLSSs) to ensure crew safety and task execution. In this work, granular silica gel (SG) support was prepared by the extrusion–spheronization (ES) method, and amine-based adsorbent pellets were synthesized by impregnating the SG support with tetraethylenepentamine (TEPA). Dynamic CO2 circulation removal tests were carried out under simulated confined space conditions in a 100 L chamber to evaluate the low concentration CO2 removal performance of the adsorbent pellets. The effect of operating parameters on CO2 removal performance was investigated by orthogonal experiments. CO2 adsorption capacity and removal efficiency were significantly affected by CO2 concentration and reaction temperature, while reaction rate was intimately depended on CO2 concentration and gas flow rate. The maximum CO2 adsorption capacity (0.55 mmol CO2/g), removal efficiency (83.25%) and reaction rate (0.93 mmol CO2/min) were achieved under the optimized conditions of 20 °C, 1.25%CO2 and 2 L/min. A kinetic equation well representing the correlation between reaction rate and CO2 concentration and gas flow rate was established. The TEPA-SG-ES adsorbent pellets exhibited satisfactory working stability, with CO2 removal efficiency and adsorption capacity slightly decreased from 83.25% and 0.55 mmol CO2/g to 75.45% and 0.53 mmol CO2/g in 10 cycles, respectively. The slight decay in CO2 adsorption performance was associated with the oxidative degradation of amine species in oxygenated atmosphere to form amide, nitrite and imine phases, and the change of amine distribution over the pellets in multiple cycles. Overall, the desired TEPA-SG-ES adsorbent pellets could be nice scavenger candidates for circulating purification of CO2 in confined spaces.

Silica-supported Schiff-based palladium nanocatalyzed cross-coupling reactions and its applications in the synthesis of antiplatelet and fungicidal

The readily available silica gel was converted into an amino functionalized silica by refluxing with 3-aminopropylthiethoxy silane. The amino functionalized silica was transformed into the respective Schiff-based ligand by the incorporation of [2,2′-bithiophene]-5,5′-dicarbaldehyde. The Pd(0) nanocatalyst on the silica gel support was developed by further processing the Schiff-based ligand with ammonium tetrachloropalladate and hydrazine. The Schiff-based Pd(0) nanocatalyst was extensively characterized using a range of spectroscopic techniques, including Raman, SEM, EDX, TEM, XRD, ICP, and XPS. Raman spectroscopy was used to confirm that the organic moietieshavebeen successfully incorporated, and XPS, XRD, and EDX analyses supported the existence of palladium species on the silicasurface. According to the TEM analysis,Pd-nanocomplexwith a size distribution of 5.3 ± 0.6 nm was found to be evenly distributed on the silica surface. Palladium was incorporated into the silica surface at a rate of 1.9 w%, according to ICP and EDX analysis. The Mizoroki-Heck and Suzuki-Miyaura coupling reactions were successfully catalyzed by the Schiff-based Pd(0) catalyst using a diverse range of aryl halides, olefines, and organoboronic acids. High yields were achieved in each example in the case for the coupling products. Despite being recoveredfrom the reaction medium and used multiple times, the catalyst still maintained the majority of its catalytic activity. Furthermore, this Schiff-based Pd(0) catalyst was used to produce biologically active molecules of Ozagrel, an antiplatelet agent and fungicidal Boscalid with high yield.

High-Performance Heterogeneous Oxidative Desulfurization Catalyst with Brønsted Acid Sites

A new heterogeneous catalyst containing two types of active sites, sulfo group and ammonium heptamolybdate, on ASKG silica gel support was synthesized. The influence of oxidation conditions (temperature, reactant ratio, reaction time) on the conversion of a model substrate, dibenzothiophene (DBT), was examined. Conditions were found for exhaustive oxidation of DBT. The catalyst synthesized is stable under the oxidation conditions and preserves its activity in five oxidation cycles. The combination of two types of active sites not only considerably enhances the catalyst performance but also reduces to a minimum the possible washout of molybdenum compounds from the support surface.

Immobilization of acetate based ionic liquids on silica gel to fabricate a prospective desulfurizing adsorbent

ABSTRACT Ionic liquids have the potential to play a significant role in mitigating the critical challenge of refractory sulfur removal from diesel. In the present investigation, a mixture of imidazolium, pyrazolium and triazolium acetate -based ionic liquids has been immobilized on silica gel using sol-gel technology at ambient temperature (25°C), yielding a novel adsorbent. The sol-gel processing route has been elucidated by Dynamic Light Scattering (DLS) and rheology study. The fabricated adsorbent has been characterized by Fourier Transfer Infra-red (FTIR) spectroscopy, X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The results reveal that the ionic liquids have been immobilized in the silica gel support. This adsorbent has been successfully applied to remove heterocyclic sulfur compounds from model diesel containing thiophene and dibenzothiophene. The highest desulfurization efficiencies achieved for thiophene and dibenzothiophene removal are 98.31 and 99.29% respectively, using an adsorbent with 15% ionic liquid loading, model diesel: adsorbent ratio of 1:0.075, an adsorption time of 60 minutes at 25°C. The system under investigation followed the Langmuir isotherm model and the adsorption performance best fitted with the Ho’s pseudo second-order kinetics.

Experimental and kinetics investigations of low-concentration CO2 adsorption on several amine-functionalized adsorbents

The rapid cleanup of endogenous CO2 has become a necessity in environmental control and life support systems (ECLSSs), to ensure crew safety and long-term task execution. The extensively used non-regenerable LiOH and soda lime adsorbents, although exhibit high CO2 storage capacities and fast kinetics, can hardly fulfill the demands of reduced launch weight and storage volume in the space- and load-limited ECLSSs. New CO2 adsorbents with desirable attributes including high CO2 uptakes, good selectivity, facile regeneration, fast adsorption and desorption kinetics, and good multicycle stability are urgently needed. We developed amine-functionalized adsorbents by loading tetraethylenepentamine (TEPA) on mesoporous supports of activated carbon (AC), aluminum oxide (AO) and silica gel (SG). The adsorbents were characterized by N2 adsorption-desorption, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM) to study their microstructural properties. CO2 adsorption capacities and kinetic performance of the adsorbents with different supports and various amine loadings (10–50 wt%) were evaluated in 2%CO2 at 20 °C. The effects of support and amine loading on the structure-performance relationships of the adsorbents were demonstrated. The TEPA-SG-20 adsorbent (20 wt% TEPA loaded on silica gel support) exhibits the highest CO2 adsorption capacity of 1.90 mmol CO2/g and the maximum amine efficiency of 0.48 mmol CO2/mmol N. TEPA-SG-20 also exhibits fast CO2 adsorption kinetics, and the Avrami fractional order kinetic model provides a satisfactory correlation of the experimental CO2 uptakes. Furthermore, the TEPA-SG-20 adsorbent can be efficiently regenerated at 110 °C with a great regeneration efficacy of 97%. The desired adsorbent also exhibits good working stability with a low loss-in-capacity of 4.32% in 10 consecutive cycles. The good CO2 adsorption performance of TEPA-SG-20 is associated with the excellent microstructural properties such as high surface area, great pore volume and uniform dispersion of amine species. Overall, the desired TEPA-SG-20 adsorbent shows promise for low-concentration CO2 removal in ECLSSs.

Liquid phase hydrogenation of phenol catalyzed by silica supported palladium to yield cyclohexanone

In the work, liquid phase hydrogenation of phenol reaction was carried out using an isothermal fixed bed catalytic reactor. The catalyst was prepared by wet impregnation of palladium precursor onto silica gel support. The effect of reaction parameters such as catalyst particle size in the range of 1–2 mm, time factor (in terms of contact time of catalyst with reactant feed) in the range of 60–250 g.min/mole, and reaction temperature in the range of 80–130 °C on the conversion of phenol and selectivity towards cyclohexanone was studied. From the results, it was observed that the conversion of phenol and selectivity of cyclohexanone were increased with the decrease of catalyst particle size. Further it was observed that the phenol conversion increased with the increase in reaction temperature from 80 to 110 °C and time factor. However, the conversion was decreased with increase in reaction temperature beyond 110 °C. A decreased trend was observed for selectivity of cyclohexanone with the increase of reaction temperature and time factor. The obtained maximum conversion of phenol was around 92% with a cyclohexanone selectivity of more than 99% at an optimum temperature of 110 °C and contact time of 250 g.min/mole in presence of Pd/SiO2 catalyst at hydrogen-to-phenol mole ratio of 1:4. It was observed furthermore that the conversion of phenol and selectivity of cyclohexanone was higher for 1 mm catalyst particle size when compared to 2 mm catalyst particle size. From the results, it can also be concluded that the developed empirical models to predict conversion of phenol and selectivity towards cyclohexanone were good in agreement with the experimental data.

A ninhydrin–thiosemicarbazone based highly selective and sensitive chromogenic sensor for Hg2+ and F− ions

This study demonstrates the design, synthesis and sensing applications of a simple and efficient chemosensor, 2-(1,3-dioxo-1H-inden-2(3H)-ylidene)hydrazinecarbothioamide (R) for quick detection of Hg2+ and F− in aqueous media using a colorimetric test, UV–Vis spectral analysis, and silica gel support. Sensor R showed the typical absorption peak at 305 nm for Hg2+ which is responsible for color change from yellow to colorless, while in the case of F−, R exhibits a major peak at 415 nm and a color change from yellow to red. The limit of detection (LOD) of R for the analysis of Hg2+ was calculated as 1×10−6 M while for F−, it was found to be 3.4×10−7 M. The binding modes of R with Hg2+ and F− have been investigated by the Job’s plot, Benesi–Hildebrand (BH) method, 1H NMR, FTIR and theoretical studies. The sensor R was reversible after treating it with reagents such as EDTA and calcium nitrate solution after contacting with Hg2+ and F−, respectively. The performance of R can be successfully applied for the analysis of F− contents present in toothpastes. A simple and efficient receptor ninhydrin-based Schiff’s base (R) for quick detection of Hg2+ and F− in aqueous medium using colorimetric and UV–Vis spectral analyses.

Towards a room temperature oxidative desulfurization of refractory compounds over 1-octyl-3-methylimidazolium tetrachloroferrates/silica gel: The beneficial effects of immobilization

A successful immobilization of 1-octyl-3-methylimidazolium tetrachloroferrates ([Omim][FeCl4]) thin films on a silica gel while remaining its mesoporousity, was accomplished in this work. The developed catalyst was highly active and cost-effective for deep oxidative desulfurization of refractory thiophenic compounds at room temperature utilizing H2O2 oxidation agent. The reaction products were well separated from fuel by the catalyst itself under a beneficial solvent-free condition. The catalyst was characterized applying different analyses of FT-IR, TGA, XRD, SEM, EDS, AFM, N2 adsorption desorption, BET, and BJH. A sufficiently large pore diameter (∼6.2 nm) and high surface area (∼490 m2/g) of the silica gel for supporting the Lewis acidic [Omim][FeCl4] having a proper anion and cation structure, synergistically enabled a high efficient and selective catalyst for removal of refractory thiophenes. The influences of reaction temperature and time, loading amount of ionic liquid (IL), catalyst and oxidant amount as crucial reaction factors were evaluated in order to have a maximum desulfurization yield. Impressively, only a very low IL loading of 5 wt.% on the silica gel support achieved complete elimination of dibenzothiophene at the optimal mild conditions and room temperature. In the presence of a non-sulfur aromatic hydrocarbon beside different thiophenic models, the desulfurization selectivity of [Omim][FeCl4] increased from 0.92 to 0.95 via immobilization on the silica gel support. A significant decline in the IL consumption was verified as another beneficial effect of this immobilization. The catalyst could be easily separated having a capability for 100 % removal of dibenzothiophene after recycling four times. Meanwhile, GC–MS analysis was employed for further founding of the desulfurization pathway.

Synthesis and investigation of highly dispersed active phases of intermetallic and supported SHS-catalysts

In the present study, the active phases (AP) of an Fe–Ni–Co–Mn catalyst produced from SHS-intermetallics (a), a catalyst prepared via formation an intermetallic layer on a mesh surface of chromium-nickel stainless steel (b), and of a Co–Mn catalyst prepared via SHS on silica gel support (c), were isolated and characterized by SEM and XRD. The catalysts studied were highly active in the process of deep oxidation and catalysts (b) and (c) were highly active in the process of CO2 methanation as well. All AP had oxo-metallic composition and were formed from nanoscale components, but if the structure of these components for catalyst (a) was the same as on the surface of the catalyst, the structures of AP components for catalyst (b) significantly differed from the surface structures. In addition, AP sediment grain nanostructures of catalyst (c) differed from those of catalysts (a) and (b).

Stability of mesocellular foam supported copper catalysts for methanol synthesis

Mesocellular foam is a well-defined mesoporous silica comprising large cages (˜20 nm), connected by small windows (2–10 nm). Here, we used mesocellular foam as a support material in the preparation of Cu based model catalyst for methanol synthesis at high temperature and pressure. To this end, we synthesized two types of mesocellular foam, with the same cage size, but a different window size of 8 and 2.3 nm, and compared them to the use of a silica gel support. Cu particles were deposited by impregnation with a copper nitrate precursor solution and decomposition in either N2 or H2-containing gas stream. We followed the phase evolution in situ, and identified a method using direct reduction in H2 to deposit 3 nm Cu particles on all different supports. The catalysts prepared on the mesocellular foam displayed a much higher stability than the silica gel supported catalysts. The impact of the window size of the MCF was small, but significant: the catalysts supported on the small window mesocellular foam were more stable on the long term. However, they also had a lower activity due to embedment of the Cu particles in the windows, as revealed with electron tomography. A higher metal loading on the small window mesocellular foam resulted in enhanced coalescence of the Cu particles, which was attributed to smaller interparticle distances. Increasing the loading on this support even further increased the size and polydispersity of the Cu nanoparticles, leading to a higher deactivation rate due to Ostwald ripening. Hence, the loading and size polydispersity are important parameters in determining the catalyst stability. We also found that the nature of the SiO2 support has more impact on the catalyst stability than the restricting pore sizes, probably due to the fact that Ostwald ripening dominates particle growth on the longer time scales.

Reverse water gas shift reaction using supported ionic liquid phase catalysts

The reverse water–gas shift reaction (RWGSR) using a supported ionic liquid-phase (SILP) catalyst consisting of Ru catalyst, ionic liquid (1-butyl-3-methylimidazolium chloride ([C4mim]Cl)), and porous silica gel support, was investigated. The catalytic activity of the SILP catalyst toward RWGSR strongly depends on the kind of Ru catalyst and amount of IL. Among the three kinds of Ru catalysts ([RuCl2(CO)3]2, Ru3(CO)12, and RuCl3), [RuCl2(CO)3]2 exhibits the best catalytic activity. Brunauer–Emmett–Teller (BET) surface area analysis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses of the SILP catalyst based on [RuCl2(CO)3]2 and [C4mim]Cl revealed that both the solvation of the active catalytic Ru species and the surface area of the ionic liquid phase strongly affect catalytic activity. Hence, these factors help to determine the optimum amount of [C4mim]Cl in the SILP catalyst. The resulting SILP catalyst, with an optimum constitution, exhibited greater catalytic activity than the homogeneous system in which the same amounts of [RuCl2(CO)3]2 and [C4mim]Cl were employed. Catalytically active Ru species during RWGSR in both systems were investigated by means of electrospray ionization-mass spectrometry (ESI-MS). Interestingly, the rate-determining step in the two systems was different, implying that the silica support lowers the activation energy of the protonation reaction in the catalytic cycle. Therefore, the facilitation of the RWGSR by a SILP catalyst system can be realized by good mass transport, derived from the large surface area, as well as the effect of the silica support on activation energy. Furthermore, 20 cycles of the RWGSR using the SILP catalyst were accomplished.

A High-Throughput Process for the Solid-Phase Purification of Synthetic DNA Sequences.

An efficient process for the purification of synthetic phosphorothioate and native DNA sequences is presented. The process is based on the use of an aminopropylated silica gel support functionalized with aminooxyalkyl functions to enable capture of DNA sequences through an oximation reaction with the keto function of a linker conjugated to the 5'-terminus of DNA sequences. Deoxyribonucleoside phosphoramidites carrying this linker, as a 5'-hydroxyl protecting group, have been synthesized for incorporation into DNA sequences during the last coupling step of a standard solid-phase synthesis protocol executed on a controlled pore glass (CPG) support. Solid-phase capture of the nucleobase- and phosphate-deprotected DNA sequences released from the CPG support is demonstrated to proceed near quantitatively. Shorter than full-length DNA sequences are first washed away from the capture support; the solid-phase purified DNA sequences are then released from this support upon reaction with tetra-n-butylammonium fluoride in dry dimethylsulfoxide (DMSO) and precipitated in tetrahydrofuran (THF). The purity of solid-phase-purified DNA sequences exceeds 98%. The simulated high-throughput and scalability features of the solid-phase purification process are demonstrated without sacrificing purity of the DNA sequences. © 2017 by John Wiley & Sons, Inc.

Effect of water on the retention on diol and amide columns in hydrophilic interaction liquid chromatography.

The amount of water adsorbed on polar columns plays important role in hydrophilic interaction liquid chromatography. It may strongly differ for the individual types of polar columns used in this separation mode. We measured adsorption isotherms of water on an amide and three diol-bonded stationary phases that differ in the chemistry of the bonded ligands and properties of the silica gel support. We studied the effects of the adsorbed water on the retention of aromatic carboxylic acids, flavonoids, benzoic acid derivatives, nucleic bases, and nucleosides in aqueous-acetonitrile mobile phases over the full composition range. The graphs of the retention factors versus the volume fraction of water in mobile phase show "U-profile" characteristic of a dual hydrophilic interaction-reversed phase retention mechanism. The minimum on the graph that marks the changing retention mechanism depends on the amount of adsorbed water. The linear solvation energy relationship model suggests that the retention in the hydrophilic interaction liquid chromatography mode is controlled mainly by proton-donor interactions in the stationary phase, depending on the column type. Finally, the accuracy of hydrophilic interaction liquid chromatography gradient prediction improves for columns that show a high water adsorption.

A Novel SiO2‐Supported Fluorine Modified Chromium–Vanadium Bimetallic Catalyst for Ethylene Polymerization and Ethylene/1‐Hexene Copolymerization

AbstractPhillips catalyst is one of the most significant industrial ethylene polymerization catalysts. Chemical modifications have been carried out to tune the Phillips catalyst performance and improve the polyethylene properties. After the modification of the catalyst by fluorine, the polyethylene product with higher molecular weight (MW) and narrower molecular weight distribution (MWD) is suitable for producing automobile fuel tanks. Vanadium containing Phillips catalyst enhances α‐olefin incorporation and MW regulation. In present work, fluorine modified and unmodified chromium–vanadium (Cr–V) bimetallic catalysts are prepared and explored. Compared with the fluorine‐free catalyst, the activities of F‐modified bimetallic catalysts slightly decrease with the increasing MW of the product and the hydrogen response increases slightly. Due to the synergistic effect of the chromium, vanadium and fluorine on the silica gel support, the short‐chain branch distribution (SCBD) of copolymers from F‐modified Cr–V bimetallic catalyst (Cr–V–F)600 is more beneficial than that of Cr–V bimetallic catalyst (Cr–V)600 and F‐modified Cr–V bimetallic catalyst (Cr–V–F)500. The fluorination of Cr–V bimetallic catalysts has not only preserved the high polyethylene activity of bimetallic active sites but also produced the advantage of the high MW ability from fluorine. image

Photochemically Immobilized 4-Methylbenzoyl Cellulose as a Powerful Chiral Stationary Phase for Enantioselective Chromatography.

A process to immobilize para-methylbenzoyl cellulose (PMBC) on silica gel has been developed and applied to prepare chiral stationary phases (CSPs) for enantioselective chromatography. The immobilization was achieved by simple irradiation of the polysaccharide derivative with ultraviolet light after coating on a silica gel support. The influence of parameters such as irradiation time and solvent on immobilization effectiveness were investigated. The performance of the prepared immobilized phases were evaluated by injection of a series of racemic compounds onto the packed columns and determination of their chiral recognition ability. By contrast to the classical coated phase, the immobilized CSP can be used under various chromatographic conditions without limitation of organic solvent types as the mobile phase. This extended applicability permits to improve selectivity and to resolve chiral compounds which are not or only poorly soluble in the mobile phases which are compatible with the non-immobilized PMBC stationary phase.

Colloidal and nanosized catalysts in organic synthesis: XV. Gas-phase hydrogenation of alkenes catalyzed by supported nickel nanoparticles

Gas-phase hydrogenation of alkenes and their derivatives, catalyzed by nickel nanoparticles supported on zeolite or silica gel support occurs at 150–250°С and an atmospheric hydrogen pressure and results in a high conversion. The selectivity of the hydrogenation depends on the amount of hydrogen: at a low diene (triene)–hydrogen ratio, selective hydrogenation of one multiple bond in the substrate is possible.

Effect of a carrier’s nature on the activation of supported iron catalysts

The effect a carrier’s nature has on the activation of supported iron catalysts in a stream of pure carbon monoxide CO is investigated. It is shown that iron is mainly present in the form of magnetite Fe3O4 in case of carbon supports and in the form of hematite Fe2O3 for silica gel supports. It is shown that all activated samples are chiefly made up of the Hagg carbide χ-Fe5C2, but its concentration is higher for the carbon supports.

Catalytic Properties of Various Types of Sulfonated Cation-Exchange Resins in the Synthesis of Isopropyl Tert-Butyl Ether

The acidic and catalytic characteristics of various types of sulfonated cation-exchange resins, differing in the location of the active phase, in the synthesis of isopropyl tert-butyl ether (IPTBE) were studied. It was established that a sulfonated cation-exchange resin on a wide-pore silica gel support has the highest selectivity with respect to IPTBE (100%). It was shown that mineral–organic sulfonated cation-exchange resins have higher activity than bulk sulfonated cation-exchange resins due to the accessibility of their acid centers for the reagents.

Immobilized catalysts for iridium-catalyzed allylic amination: rate enhancement by immobilization.

The first immobilized catalyst for Ir-catalyzed asymmetric allylic aminations is described. The catalyst is a cationic (π-allyl)Ir complex bound by cation exchange to an anionic silica gel support. Preparation of the catalyst is facile, and the supported catalyst displayed considerably enhanced activity compared with the parent homogeneous catalyst. Up to 43 consecutive amination runs were possible in recycling experiments.

Evaluation of differences between Chiralpak IA and Chiralpak AD-RH amylose-based chiral stationary phases in reversed-phase high-performance liquid chromatography.

Polysaccharide-based chiral stationary phases can be used for the enantioselective separation of a wide range of structurally different compounds. These phases are available with chiral selectors coated or immobilized on silica gel support. The means of attachment of the chiral selector to the carrier can influence the separation performance of these stationary phases. This paper deals with evaluation of differences in the separation abilities of coated Chiralpak AD-RH versus immobilized Chiralpak IA amylose-based stationary phases in the reversed-phase mode of high-performance liquid chromatography. A set of chiral analytes was separated under acidic and basic conditions. Differences were observed in the enantioseparation potential of the tested phases. The linear-free energy relationship and additional evaluation of ionic interactions were used to ascertain whether the interactions that participate in retention and enantioseparation are affected by the means of preparation of these phases. All the interactions covered by the linear-free energy relationship were significant for the studied phases and their absolute values were almost always higher for the coated phase. Ionic interactions were found to be more important on the immobilized stationary phase but did not contribute to any improvement in the enantioselective separation performance.