A novel titanosilicate with MWW topology, Ti-MWW, exhibits a behavior not observed on other titanosilicates such as TS-1, TS-2 and Ti-beta, in that it selectively epoxidizes trans isomers from a mixture of cis/trans alkenes with retention of stereochemistry.

A new titanosilicate, named Del-Ti-MWW, has been prepared by delaminating the lamellar precursor of Ti-MWW, which is postsynthesized from highly deboronated MWW zeolite with the assistance of cyclic amine. The amount of organic base used for supporting surfactant in swelling the layered structure should be controlled carefully to delaminate efficiently without the collapse of the structure. Ultrasound treatment is demonstrated to delaminate the swollen material more completely. Del-Ti-MWW materials have a large surface area, which mitigates effectively the steric restrictions imposed by conventional microporous titanosilicates to bulky molecules. Del-Ti-MWW, maintaining the fundamental structure of MWW zeolite and tetrahedral Ti species in the framework position, proves to be superior to TS-1, Ti-Beta, three-dimensional Ti-MWW and even mesoporous Ti-MCM-41 in the epoxidation of a wide range of bulky alkenes with hydrogen peroxide.

Novel methods for enhancing the epoxide selectivity in the alkene epoxidation over [Ti,Al]-Beta have been developed. When as-synthesized [Ti,Al]-Beta was treated with aqueous ammonium nitrate solution and successively calcined at low temperature, a dramatic enhancement of epoxide selectivity was attained in the liquid-phase epoxidation of cyclohexene using H2O2 as an oxidant in protic solvent methanol. The optimum thermal treatment temperature to achieve the maximum epoxide yield was 473 K, where the postsynthetic [Ti,Al]-Beta exhibited a catalytic activity comparable to the sample directly calcined at 793 K; nevertheless, the epoxide selectivity was as high as 63% for the former in contrast to 0% for the latter. The ion-exchange treatments with quaternary ammonium salts over calcined [Ti,Al]-Beta showed similar effects, although the treatments with alkali and alkaline earth metal ions were detrimental to the catalytic activity. It is suggested that the quaternary ammonium cations selectively blocked the acid sites deriving from the framework Al, which resulted in preventing the ring-opening hydrolysis of the epoxide, whereas the inorganic cations poisoned not only the acid sites but also the Ti active sites contributing to the catalytic epoxidation. The ion-exchanged catalyst was regenerated readily by repeated calcination and following ion exchange and thus turned out to be an active, selective, and reusable epoxidation catalyst.

Titanosilicate catalysts are of scientific and technological interest because of their ability to be applied to environmentally friendly chemical processes for the liquid-phase catalytic oxidation of a variety of organic compounds, by using H2O2 as a clean oxidant. The medium-sized pore

A novel titanosilicate with MWW topology, Ti-MWW, has been prepared by an acid treatment on a corresponding lamellar precursor which is hydrothermally synthesized with the coexistence of boron and titanium using piperidine (PI) or hexamethyleneimine (HM) as a structure-directing agent. TheMWWprecursor can be synthesized to have a Si/Ti ratio as low as 10 when the Si/B ratio of the gel is maintained at 0.75. Both the materials synthesized using PI and HM exhibit the crystal form of thin platelets, while the latter shows a larger crystal size. Besides the tetrahedral Ti species, the precursor always contains the octahedral Ti species showing a UV-vis band at 260nm, regardless of the Ti content. Calcination of the precursor results in a partial condensation of the octahedral Ti species to form the anatase phase, which is hardly removed by the acid treatment. MWW-type titanosilicate nearly free of both anatase and boron, however, is successively prepared by a cyclic treatment on the lamellar precursor, that is, an acid treatment, subsequent calcination, and a further acid treatment. After evacuation at 773K, the titanosilicate thus prepared shows a characteristic IR band at 960cm-1 not observed for the Ti-free sample. The intensity of the 960 cm-1 band increases linearly with the Ti content up to a level corresponding to Si/Ti) 40, indicating the limitation of incorporating Ti into the framework of MWW by the present method.