铈改性对HZSM-5分子筛表面性质及其催化降解甲硫醇(CH_3SH)的研究

Effect of Cerium Doping on Surface Properties and Catalytic Activity of HZSM-5 Zeolites in Decomposition of Methyl Mercaptan

采用浸渍法制备了Ce改性的HZSM-5分子筛催化剂,考察Ce改性前后HZSM-5分子筛催化分解甲硫醇反应中的催化活性。通过XRD,BET,H_2-TPR,NH_3-TPD和CO_2-TPD等手段对其物化性能进行表征,结果表明：Ce改性后HZSM-5分子筛的结构没有被破坏,而Ce的引入可明显提高催化剂的还原性能,进而促进甲硫醇的催化分解;同时Ce的引入还能有效调控HZSM-5分子筛表面的酸碱性,可明显增加分子筛表面碱性中心的数量,从而显著提高催化分解甲硫醇的活性。此外,探讨了在350-650℃范围内焙烧温度对Ce改性HZSM-5分子筛表面性质及催化分解甲硫醇活性的影响。实验结果表明,在550℃焙烧获得的分子筛催化分解甲硫醇的效果最好。表征结果显示：当焙烧温度较低时,Ce与HZSM-5分子筛的相互作用较弱,所以分子筛催化分解甲硫醇的活性较差,随着焙烧温度的升高,分子筛的还原性能和酸碱性能均有所降低;当焙烧温度过高时,导致Ce O_2相互堆叠形成新的介孔孔道坍塌,降低其催化分解甲硫醇的活性。

Rare earth Ce modified HZSM-5 catalysts were prepared by an incipient-wetness impregnation method,and the influence of different calcination temperatures on the activity of CH_3 SH catalytic decomposition were investigated. The physical and chemical properties of the synthesized catalysts were characterized by XRD,BET,H_2-TPR,NH_3-TPD and CO_2-TPD. The results showed that doping of Ce would not destroy the framework structure of HZSM-5,while the existence of Ce O_2 phase in HZSM-5 catalysts improved the reducibility of the catalysts,which should be in favor of the catalytic decomposition of CH_3 SH. Furthermore,the introduction of Ce could effectively regulate the acidity and basicity,which may affect the catalytic activity of decomposition of CH_3 SH. The effect of calcination temperature between 350 and 650 ℃ was investigated on the surface properties and catalytic activity in decomposition of CH_3 SH of these catalysts. The sample HZSM-5 calcined at 550 ℃ exhibited the best catalytic activity in decomposition of CH_3 SH. The characterization results indicated that when the calcination temperature was low,the interaction between cerium and HZSM-5 zeolite is weaker,which decreased the activity of catalytic decomposition of CH_3 SH. With the increase of calcination temperature,the reducibility and the acid-base properties of the catalysts were decreased. When the calcination temperature was higher,resulting in Ce O_2 mutually stacked to form new mesoporous pore collapse,which should reduce its catalytic decomposition activity of CH_3 SH.