超声波碱处理改性对丝光沸石结构、酸性质及其催化性能的影响

Effect of ultrasonic alkali treatment on structural, acidic properties and performance of MOR catalyst

基于丝光沸石(MOR)催化合成乙酸甲酯稳定性较差及传统碱处理MOR较难引入多级孔的特性,提出了利用超声波对MOR进行碱处理脱硅改性以制备多级孔MOR的技术。采用XRD、SEM、TEM、吡啶红外和N2吸-脱附等手段对催化剂进行了表征,分别考察了超声波在不同碱浓度处理改性条件下对分子筛催化剂骨架结构、酸性质、孔结构以及催化合成乙酸甲酯性能的影响。结果表明,通过超声波及合适浓度的Na OH碱溶液处理后,MOR分子筛的酸量、介孔孔容、比表面积都增加、孔径分布变宽,催化剂的活性和稳定性等催化性能得以改善。改性后的MOR催化剂二甲醚(DME)转化率由35.3%增加到44.8%,使用寿命大大延长,但碱液浓度过高会严重破坏MOR分子筛骨架结构,催化活性及稳定性快速下降。

MOR catalyst commonly suffers the poor stability in the catalytic synthesis of methyl acetate. It’s difficulty to introduce the hierarchical pores by traditional alkali treatment. To overcome this drawback, an ultrasonic alkali treatment was utilized to generate hierarchical MOR via desilication. Multiple analyzing methods, such as XRD, SEM, TEM, pyridine IR and N2 adsorption-desorption, were used to characterize the catalyst structure and the influence of ultrasonic treatment under different alkali concentration on the MOR framework. Acidity, pore structure and catalytic properties were investigated. The results showed that a proper ultrasonic alkali treatment could significantly improve the number of acidic sites, mesopore volume, surface area, pore size distribution, catalytic activity and stability. The DME conversion increased from 35.3% to 44.8%, and the catalyst lifetime was greatly prolonged. However, an excessive alkali concentration seriously destroyed the MOR framework, leading to a rapid decrease on catalyst activity and stability.