关键词: 离子蚀刻, 晶貌, TS-1, 结晶度, 活性位

Abstract: A post-synthesis modification method, named ion etching, is proposed to adjust the morphology of titanium silicalite TS-1 for a better catalytic activity. The new method mainlYINvolves treating titanium silicalite TS-1 with an ammonia-containing aqueous solution in autoclave under the conditions of ca. ammonia aqueous solution concentration 0.5-14 mol/L NH₃, volume ratio of liquid/solid 20-100, hydrothermal temperature 100-180 ℃ and contact time 24-500 h. According to the characterizations by SEM, XRF, XRD, FTIR and UV-Vis, the modification can transform a well-defined large crystal TS-1[1 μm×2 μm×6 μm, n(Si)/n(Ti)=53.62] into fine grains which can avoid falling off from the matrix if the conditions of the treatment are properly controlled. The effect of ion etching upon TS-1 morphology is attributed to the OH -ion(derives from NH₃·H₂O) catalyzed hydrolysis of the T-O-T bridge bond of the silicic zeolitic framework. Its main advantages over mechanical ball-millingthe conventional zeolitic morphology modification method, include actually fully retained crystallinity and almost intact coordination state of the active Ti sites of the remained framework, as confirmed by XRD, FTIR and UV-Vis. Probe reaction shows that, the large crystal TS-1 modified by the present method at 170 ℃ for 129 h, when used as the catalyst for epoxidation of propylene, could be operated at propylene weight hourly space velocity of 0.5h_-1, and 97.85% hydrogen peroxide conversion and 96.87% propylene oxide selectivity were obtained. However, to reach comparative hydrogen peroxide conversion, the intact zeolite could only be operated under propylene weight hourly space velocity of 0.2h_-1. The remarkable increase of the catalytic activity of the modified TS-1 may be attributed to the improved intra-crystal diffusivity and the excellent preservation of the crystallinity and active Ti sites by the present modification.

Key words: Ion etching, Morphology, TS-1, Crystallinity, Active site