Structure Modifications Of Crystalline Zeolites And Catalytic Properties Of Solid Acids

The dissertation has been carried out to develop novel solid acid catalyst based on the structural modification and incorporation of active species into MWW and MFI-type zeolites, and to investigate their catalytic properties as solid acid catalyst and their potential applications to the clean processes for producing fine chemicals.In the first part, we have developed a novel methodology for synthesizing a new aluminosilicate composed of MWW sheets but with expanded interlayer pore windows. The method was based on a strategy of inserting monomeric Si source into the interlayer spaces through alkoxysilylation of interlayer-silanols followed by removing organic moieties. The effects of post-treatment conditions including Si/Al molar ratios of precursors, amount of silylation agent, concentration and amount of nitric acid, temperature and strength of post-treatment on the structure change and properties were investigated in details. The large pore aluminosilicate Al-MWW (IEZ-Al-MWW) catalysts showed higher activities in the Beckmann rearrangement of cyclohexanone oxime in comparison to 3D Al-MWW, due to possessing much open reaction spaces which were accessible to the substrates with large molecular dimensions.In the second part, a simple post-treatment method has been developed to prepare MCM-56 analogue from Al-MWW lamellar precursors made up of MWW sheets. The method was based on the flexibility of Al-MWW lamellar precursors. Acid-treating the MWW precursors at temperatures lower than 353 K and nitric acid concentration lower than 5 M led to partially delaminated structure of MCM-56 even after further calcination, whereas the acid treatment at higher temperatures such as refluxing and higher nitric acid concentration only resulted in conventional 3D MWW structure. In addition, the construction of MCM-56 structure depended greatly on the amount of template remaining in the result samples, that is, the structural transformation of MCM-56 was achieved only for the samples with a moderate amount of remaining template. The post-treatemt method was also applicable to ERB-1 system. Thus, using this post-treatment method, MCM-56 with a wide range of Al content was achieved. Compared with 3D Al-MWW, MCM-56 had a larger external surface, which mitigated effectively the steric restrictions to bulky molecules imposed by the intracrystal micropores. The MCM-56 was then superior to 3D Al-MWW in the cracking of 1,3,5-triisopropylbenzene.In the third part, a novel and suitable catalyst in the intermolecular condensation of EDA was designed by adjusting the Ti content and crystal size based on TS-1 which has a unique pore structure and moderate acidity. TS-1 is superior to other titanosilicates in the intermolecular condensation of EDA to TEDA, giving EDA conversion high as 95% and a total selectivity of ca.85% to PIP and TEDA under optimum reaction conditions when TS-1 is synthesized to have small a crystal size (0.3-0.4μm) as well as a high Ti content (Si/Ti=30). Comparing with the activity and FT-IR results of TS-1 catalysts exchanged with Na+ and acid treatment, we deduce that it is the moderate acidic internal silanols, which are adjacent to the "open" Ti sites in TS-1, contribute to the condensation of EDA rather than the Lewis acid sites related to the framework Ti. In addition, according to the activity of TS-1 with various crystal sizes, we deduce the secondary condensation of PIP to TEDA, a bulky reaction which requires open reaction spaces mainly occurred in pore entrance and external surface, however, the primary condensation of EDA to PIP took place mainly in the channels.In the fourth part, a novel and suitable catalyst in the intermolecular condensation of EDA was designed by adjusting the Al content and crystal size based on the role of ZSM-5 in acid-catalyzed reactions. Through comparing with the activity results of ZSM-5 catalysts with various Al content, we can deduce that it is the Bronsted acid related to framework Al contributes to the condensation of EDA. ZSM-5 catalyst having medium Al content (Si/Al=l 10) and smaller crystal size (100 nm) gave EDA conversion high as 99% and a selectivity of ca.75% to TEDA under optimum reaction conditions. In addition, according to the activity of uncalcined Na-ZSM-5 with acid treatment, we can deduce the primary condensation of EDA to PIP occurred mainly in the channel, while the pore entrance and external surface played an important role in the secondary condensation of PIP to TEDA.