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Study on Synthesis and Acid-base Bifunctionalized Mesoporous Materials MCM-41

Author: LiangLiZhi
Tutor: HanJinYu
School: Tianjin University
Course: Chemical processes
Keywords: mesoporous material MCM-41 hydrothermal method solid state ionics migration acidic-basic bifunctionalization
CLC: O613.72
Type: Master's thesis
Year: 2009
Downloads: 174
Quote: 1
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Abstract


Ascribing to their excellent textural properties, including highly ordered pore channels, controllable narrow pore size distribution, large surface area, as well as a large amounts of Si-OH, which can facilitate the modification of their surface with metals and organic group, the functionalization of mesoporous silica MCM-41 has attracted more and more attention. And in many cases, the synergism of the acid-base active centres usually contributes to promote the progress of the reaction, and results in an enhancement of the reaction velocity, in an improvement of the selectivity and in a prolongation of the catalyst life. Therefore, acid-basic bifunctional mesoporous materials, which could combine the advantages of mesoporous structure and acid-basic properties, that is, combining the specific chemical reactivity of the acid-basic groups with attractive structure properties, have generated considerable interest in their application such as shape-selective catalysis, adsorption-separation processes, and other fields. In this work, we attempt to develop new facile and efficient strategies for the acidic-basic bifunctionalization of mesoporous silica MCM-41.By the hydrothermal method, pure siliceous mesoporous MCM-41 samples were synthesized in different alkaline media (sodium hydroxide, TMAH, ammonia, ethylamne, ethylenediamine) by using cetyltrimethylammonium bromide as the template and tetrarthyl orthosilicate as the silica source. a series of different alkaline medium surface-modified mesoporous silicas MgO-ZrO2–MCM-41(MZ–MCM-41) endowed with acid-base properties have been successfully synthesized in one pot by the introdintroduction of zirconium and magnesium salts into the initial mixture of synthesizing mesoporous silica (MCM-41). The characterization results indicated the resultant nanocomposites exhibit excellent acid-basic properties with well periodically ordered mesoporous backbone. MCM-41 sythesized in a weak organic base is of a higher quality than that synthesized in NaOH medium. A weak organicbase, like ethylenediamine, yields the product samples of higher structural order, higher crystallinity. And the mechanism and inherent rules of bifuctionalization was also investigated.A new acidic-basic bifunctional approach with high efficiency and facility, named solid state ionics migration, for mesoporous silica was developed. The generation of acid-base active sites and removal of host template were achieved in a single step by this method. A series of acid-base bifunctional mesoporous nanocomposites MgO-Al2O3–MCM-41 (MA–MCM-41) have been successfully synthesized by means of this approach. The characterization results indicated that the resultant bifunctional mesoporous nanocomposites can keep mesoporous framework well, and the guest species can be efficiently introduced into the channel and fully dispersed on the surface of the host. The electric positive Mg2+ and Al3+ can form covalent bonds between the metal ions and the oxygen atoms of the Si-OH groups on the surface of the host during calcination. Hence, the Si–O–Mg and/or Si–O–Al interlinkages can conveniently establish between the mesoporous host and the introduced guests to achieve the bifuctionalization. The results of NH3-TPD and CO2-TPD indicated the acidic sites and basic sites co-exist on the surface of the mesoporous nanocomposites synthesized by the titled method.

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CLC: > Mathematical sciences and chemical > Chemistry > Inorganic Chemistry > Non-metallic elements and their compounds > Part Ⅳ family of non-metallic elements (carbon and silicon ) and its compounds > Si Si
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