Catalytic activity of polymer–montmorillonite composites in chemical reactions (original) (raw)
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Clay minerals possess unique physical properties such as high Lewis acidity, high specific surface area, periodic layer structures, and these materials can be utilized as polyolefin catalysts supports. This work focused on the influence of structural and surface properties of montmorillonite (MMT) on the catalytic ethylene polymerization performances. The structural parameter, specific surface area and compositions of the MMTs under different chemical modification conditions were measured by X-ray diffraction (XRD) analyses, multipoint BET method and X-ray fluorescence spectrometer (XRF) methods. The basal spacing value increased when samples were treated with H 2 SO 4 /Li 2 SO 4 combination while the value remained nearly constant when the samples were treated withH 2 SO 4 solution alone. Majority of elements Ca, Mg, K are leached out after the acid treatment. Ethylene polymerization results showed that MMTs treated with H 2 SO 4 /Li 2 SO 4 combination, activated with triethylaluminum (TEA), exhibit higher polymerization activity, reached the level of methylaluminoxane (MAO) activated supports. It can be attributed to the relatively wider interlayer space which had more reactive sites for chemically anchoring metallocene catalysts.
Polymer, 1994
Non-extractable poly(methyl methacrylate) (PMMA)-montmorillonite adducts were prepared by two distinct processes: (a) In the first method, free-radical copolymerization of MMA with clay previously treated with 2-(N-methyl-N,N-diethylammonium iodide) ethyl acrylate (QD1) or 2-(N-butyl-N,N-diethylammonium bromide) ethyl acrylate (QD4) was performed. (b) The second method was based on the direct interaction of montmorillonite with various copolymers of MMA with QD1 or QD4. The structure of the adducts as determined by Fourier-transform infra-red spectroscopy, thermogravimetric analysis and X-ray diffraction was shown to consist of the insertion of MMA macromolecules between lamellar layers whose separation was consequently higher than in the polymer-free clay. The polymer was strongly fixed to the inorganic surfaces, probably due to cooperative formation of electrostatic bonding. The thermal stability of the organic polymers was substantially enhanced in the adducts.
Advanced Powder Technology, 2017
Three component coupling reactions of aldehyde, b-ketoester (or b-diketone) and urea (or substituted 29 urea) were carried out by using acid activated montmorillonite clay (AT-Mont.) catalyst having surface 30 area about 400 m 2 /g for the facile synthesis of 3,4-dihydropyrimidin-2(1H)-ones via the Biginelli reac-31 tions under mild reaction conditions. The activation of montmorillonite clay was carried out with HCl 32 under controlled conditions for generating nanopores (size 2-7 nm) into the matrix. This porous catalyst 33 has promising feature for Biginelli reaction such as easy removal of the catalyst, short reaction time, high 34 yield with 100% selectivity and easy workup procedure. Powder XRD, SEM-EDX, N 2 adsorption, pyridine 35 adsorbed FT-IR and TPD analysis were carried out to characterize the solid porous AT-Mont. The catalysts 36 can be recycled and reused several times without significant loss of their catalytic activity.
Applied Catalysis A: General, 2002
Two montmorillonites STx-1 (Texas) and SWy-2 (Wyoming) were first activated with different amounts of 12 M HCl and then exchanged with a fixed amount of 1 M tetramethylammonium (TMA + ) chloride solution (H/TMA samples) at room temperature. TMA + -exchanged samples and then acid activated (TMA/H samples) were also prepared to evaluate the resistance to displacement of TMA + by protons. The surface area and the acidity were determined by BET and cyclohexylamine adsorption methods, respectively. The catalytic activity of these acid activated organoclays was directly measured using the isomerization of 1-butene at 300 • C to yield cis-and trans-2-butene. The total conversion for the isomerization of 1-butene was higher for the TMA/H-samples (70 and 47% for SWy-2 and STx-1, respectively) than for the H/TMA-samples (51 and 25% for SWy-2 and STx-1, respectively). TMA + cations adsorbed on the clays were extremely resistant to exchange by protons, but protons were easily displaced by TMA + cations.
Asian Journal of Chemistry, 2016
In this work, the styrene polymerization catalyzed by maghnite, an Algerian typical montmorillonite sheet silicate clay is reported. As a first step, the physicochemical variation in maghnite by sulfuric acid activation and the catalytic efficiency of maghnite (Mag) and maghnite-H + (Mag-H) were studied. Acid activated maghnite were characterized by X-ray fluorescence, X-ray diffraction and FTIR. Then, the polymerization of styrene catalyzed by Mag-H was investigated. It was found that the cationic polymerization of styrene is initiated by Mag-H at ambient temperature in bulk. The effect of the amount of Mag-H, the temperature and the solvent was studied. The conversion increased with increase in the temperature and the proportion of catalyst and it was larger in nonpolar solvents. These results indicated the cationic nature of the polymerization. It was suggested that both the Lewis and the Brønsted acid sites are responsible for the catalytic activity. However, acid treatment of maghnite increases the catalytic activity and the polymerization of styrene was initiated mainly by H + .
The Journal of Physical Chemistry B, 1999
SWy-2 (Wyoming), STx-1 (Texas), and SAz-1 (Cheto, Arizona) montmorillonite and Sap-Ca saponite (California) were treated with different amounts of 12 M HCl and 1 M tetramethylammonium (TMA + ) chloride solution at room temperature. The catalytic activity of these hybrid acid-activated organoclays (AAOCs) was directly measured using the isomerization of R-pinene at 120°C for 1 h to yield camphene, limonene, and other minor products and compared to clays acid-treated in the absence of TMA + cations. The total conversion for the isomerization of R-pinene was excellent for AAOCs formed from SWy-2 (88%) and STx-1 (73%), moderate for Sap-Ca (50%), and low for SAz-1 (20%). Samples treated with TMA + alone did not exhibit any marked catalytic activity. Acid-treated Sap-Ca and STx-1, which contained no TMA + cations were also effective catalysts for the isomerization process. TMA + cations were unexpectedly resistant to exchange by protons.
An improved route for the synthesis of Al13-pillared montmorillonite catalysts
Journal of Porous Materials, 2007
The distribution of Al13 pillars and the process of intercalation in montmorillonite can be enhanced through the application of an ultrasonic treatment. This paper describes the results of ultrasonic treatment in the preparation of Al-pillared montmorillonite with and without prior exchange with Na+. The resulting materials have been characterised by X-ray diffraction (XRD), N2 adsorption/desorption, Scanning Electron Microscopy and Atomic Force Microscopy (AFM). The catalytic activity was tested with the n-heptane hydroconversion test. Optimum results were obtained after ultrasonic treatment up to 20 min without prior Na-exchange before the Al13 intercalation. Longer ultrasonic treatment resulted in partial destruction of the pillared structure. The pore size diameter also increased with increasing ultrasonic treatment up to 20 min with values in the range of 4 nm. This behaviour can be explained by the loss of the typical house of cards structure after prolonged ultrasonic treatment. AFM showed that the pillars in the interlayer of the montmorillonite resulted in a distortion of the tetrahedral sheets of the clay. At atomic scale resolution it was clear that the pillar distribution is not homogenous, confirming earlier results using high resolution TEM. The effects of ultrasonic treatment on the catalytic activity is rather limited, although the pillared clays prepared with short ultrasonic treatments of 5 and 10 min performed slightly better.