研究了以异丙苯过氧化氢为氧化剂选择氧化内烯制环氧丙烷的Ti/HMS催化剂的失活原因.采用XRD(X射线衍射),FT-IR(傅里叶变换红外光谱),UV-Vis(紫外-可见光谱)和TG(热重分析)等技术表征了催化剂失活前后的结构和化学组成.结果表明,催化剂的失活主要是由于反应过程中所产生的重组分在催化剂表面吸附,覆盖了活性中心所致;并不是由于四配位的活件钛物种转化为六配位、八配位或者锐钛矿TiO_2所致.采用热异丙苯溶剂洗涤的方法可以部分恢复失活催化剂的活性,但不能恢复到新鲜催化剂的水平:采用低温烧炭方法能够使催化剂的活性恢复到新鲜催化剂的水平.因此,Ti/HMS催化剂的失活是可逆的,采用合适的再生方法可以恢复其催化活性.
Using cumene hydroperoxide as an oxidant,the deactivation and regeneration of the Ti/HMS(titanium-containing hexagonal mesoporous silica)catalyst were studied for epoxidation of propylene to propylene oxide.The structure and surface species of the fresh and used catalysts were characterized by X-ray diffraction.Fourier transform infrared spectroscopy,ultraviolet-visible spectroscopy,and thermogravimetry analysis.The results indicated that the main reason for catalyst deactivation was that the active sites on the catalyst surface were covered by polymer molecules produced during the reaction.The catalyst deactivation was not due to the transformation of tetra-coordinated Ti species to hexa-coordinated,octa-coordinated,or even anatase species.Hot cumene washing could partly restore the catalyst activity,but the low-temperature carbon-burning could restore the catalyst activity nearly to the level of fresh one.Therefore,the deactivated Ti/HMS catalyst Was renewable and its activity could be restored by a proper regeneration method.
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