A Study On Novel Synthesis Methods For Ti-MWW And Their Catalytic Properties

In this thesis, two new methods have been explored to synthesize Ti-MWW with improved catalytic performance. Mesoporous Ti-MWW was synthesized to investigate the oxidation of macromolecules such as picoline. The catalytic properties of Ti-MWW has been investigated in the oxidation of pyridine and pyridine derivatives with hydrogen peroxide.The first part of this thesis describes a novel hydrothermal synthesis of Ti-MWW using cheap inorganic titanium source H2TiF6. Synthesis conditions, such as the amounts of H3BO3 and structure-directing agent (piperidine), were systematically studied. Compared to the use of traditional Ti source of TBOT for the synthesis of Ti-MWW (Ti-MWW-TBOT), the use of H2TiF6 (Ti-MWW-H2TiF6) reduced the amount of H3BO3 by 60%. Furthermore, Ti-MWW-H2TiF6 and Ti-MWW-TBOT exhibit significant difference in physicochemical properties. XRD shows that the layered structure of Ti-MWW-H2TiF6 is unaffected after calcination at high temperature. IR reveals they contains a lower Si-O-H content, implying that Ti-MWW-H2TiF6 is more hydrophobic than Ti-MWW-TBOT. In addition, shift in the IR adsorption band for Si-O-Ti was observed at 930 cm-1 instead of the 960 cm-1 band of Ti-MWW-TBOT. Ti-MWW-H2TiF6 is also shown to be two times more active than Ti-MWW-TBOT in the epoxidation of cyclohexene and oxidation of picoline.In the second part of this thesis, Ti-MWW without extraframework Ti was synthesized by liquid-solid isomorphous substitution reaction with H2TiF6. The particular structure of MWW enables Ti to occupy the defect sites in the framework. Ti was introduced into the framework of MWW at room temperature using H2TiF6 as the titanium source. Because fluoride ion may prefer to react with the Si-O-H on the external surface of the sheets, this prevents the formation of the extraframework Ti species. Different conditions to producing titanosilicate such as temperature, time of isomorphous substitution reaction, type of precursor, titanium source, ratio of titanium to silica and the amount of acid used for pretreatment of the precursor were investigated. IEZ-Ti-MWW catalysts with high titanium content were also produced by this simple method. The catalytic activity of Ti-MWW is far higher than the catalysts synthesized by all the other methods. Without acid treatment, the Ti-MWW catalyst could be used in catalytic reaction directly, which avoids the formation of harmful substance and waste water.In the third part of this thesis, we demonstrate a simple and versatile method for the preparation of mesoporous Ti-MWW. This method applies in situ generation of the required carbon template by decomposition of the carbohydrate directly onto the silica raw material used for the Ti-MWW synthesis. Most importantly, it allows careful control of the porosity of the mesoporous Ti-MWW in a very simple manner and it does not depend on the availability of specialized carbon templates. The physicochemical properties of the samples were characterized by various techniques and their catalytic performance was investigated by the oxidation of pyridine and picoline with hydrogen peroxide.In the last part of this thesis, the oxidation of pyridine to pyridine-N-oxide (PNO) with hydrogen peroxide has been investigated on various titanosilicate catalysts. Superior to other titanosilicates like TS-1, Ti-Beta and Ti-MOR, Ti-MWW showed a higher catalytic activity and product selectivity. The reaction parameters such as solvent, temperature, the ratio of hydrogen peroxide to substrate, the amount of catalyst and Ti content were optimized to maximize the PNO yield. Ti-MWW was capable of giving pyridine conversion and PNO selectivity both over 99% under optimum reaction conditions. Ti-MWW was a highly active, selective, and reusable catalyst for the synthesis of PNO The mechanism for the oxidation of pyridine over titanosilicates has also been considered. Ti-MWW was further structurally modified to posses open reaction spaces by interlayer expansion, which reduced the diffusion limitations in the oxidation of pyridine derivatives with bulkier molecular dimensions.