Preparation and catalytic properties of a novel titanosilicate structurally analogous to lamellar MWW precursor

摘要

A novel titanosilicate denoted as Ti-YNU-1, structurally analogous to MWW lamellar precursor, has been prepared from postsynthesized Ti-containing MWW precursor by acid treatment and subsequent calcination, and its structural and catalytic properties have been investigated extensively in comparison to three dimensional (3 D) Ti-MWW, TS-1, Ti-MOR and Ti-Beta. The formation of Ti-YNU-1 depends greatly on the Si/Ti molar ratio of Ti-containing MWW precursor; Ti-YUN-1 is selectively obtained when the Si/Ti ratio is over 70. Ti-YNU-1 has an enlarged pore entrance by 2.5 A than 3 D Ti-MWW as evidenced by XRD and TEM investigations. The lamellar structure in Ti-YNU-1 is presumably due to the presence of silanol groups, related to the defect sites not filled up by Ti at high Si/Ti ratios, which causes the stacking faults when the intercalated piperidine is removed by acid treatment. Irrespetive of a lower Ti content, Ti-YNU shows the highest conversion in the epoxidation of cyclohexene. The results of epoxidation of cycloalkenes differing in molecular size indicate the average pore size follows an order of Ti-Beta>Ti-YNU-1>Ti-MOR>TS-1>3 D Ti-MWW.