Mesoporous MCM-48 synthesized from rice husk ash silica : physicochemical properties and its catalytic activity in acylation reaction
The cubic structural mesoporous molecular sieves Si-MCM-48 has been successfully controlled by optimizing the gel compositions via a mixed surfactant templating route using cationic cetyltrimethylammonium bromide (CTABr) and neutral Triton X-100 (TX-100) surfactants. Rice husk ash, an agricultural w...
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| Format: | Thesis |
| Language: | English |
| Published: |
2005
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| Subjects: | |
| Online Access: | http://eprints.utm.my/id/eprint/4296/1/LauChinGuanMFS2005.pdf |
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| Summary: | The cubic structural mesoporous molecular sieves Si-MCM-48 has been successfully controlled by optimizing the gel compositions via a mixed surfactant templating route using cationic cetyltrimethylammonium bromide (CTABr) and neutral Triton X-100 (TX-100) surfactants. Rice husk ash, an agricultural waste obtained from an open burning site with high silica content (93 % SiO2) has been utilized as active silica reagent in the synthesis process. The Si-MCM-48 mesoporous materials were structurally characterized by X-Ray Powder Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). The results show that the crystallinity and phases of the products depend on the compositions of Na2O, surfactants, H2O and pH values. Moreover, 13C CP/MAS NMR technique had been developed to quantify a mixture of cubic MCM-48 and hexagonal MCM-41 mesophases by means of interpretation of their surfactant organization, which cannot be determined by XRD technique. In order to generate active sites for catalytic applications, aluminomesoporous materials Al-MCM-48 were prepared by post-synthesis alumination of mesoporous Si-MCM-48 and post-synthesis alumination of Si-MCM-48 mesophase using sodium aluminate as the aluminium reagent. The aluminated MCM-48 materials were characterized using XRD, 27Al MAS NMR, FTIR and nitrogen adsorption-desorption measurements. The results reveal that unimodal Al-MCM-48, which possesses narrow pore size distribution around 26Ã…, had been synthesized from post-synthesis alumination of mesoporous Si-MCM-48. Whereas, bimodal Al- MCM-48, which possesses dual narrow pore size distributions around 26 Ã… and 38 Ã… had been generated by post-synthesis alumination of uncalcined Si-MCM-48 mesophase. 27Al MAS NMR results depict that aluminium had been tetrahedrally incorporated into the framework structure of MCM-48. The nature and the concentration of acid sites of Al-MCM-48 materials have been monitored by IR spectroscopy using pyridine as the probe molecule and temperature-programmed desorption of ammonia (TPDA). Acidity studies on the samples demonstrated that the acidity strength of samples prepared via post-synthesis alumination of mesoporous Si-MCM-48 is greater than samples prepared via post-synthesis alumination of Si-MCM-48 mesophase. Aluminated MCM-48 materials have been employed in the acylation of bulky aromatic compound, 2-methoxynaphthalene with acetic chloride to produce 2-acetyl-6-methoxynaphthalene, which is intermediate for preparing naproxen, a non-steroidal anti inflammation drug. Catalytic activities have been investigated in solvents with different polarity and the results illustrate that the conversion and selectivities of products rely on the polarity of solvent. The conversion of the 2-methoxynaphthalene can be as high as 42 % with 86 % selectivities towards the desired 2-acetyl-6-methoxynaphthalene in polar solvent, nitrobenzene. Whereas, the conversion of the 2-methoxynaphthalene is 30 % with 56 % selectivity of 2-acetyl-6-methoxynaphthalene in non-polar solvent, cyclohexane. |
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