ZSM-5分子筛形貌及硅铝比对甲缩醛气相羰基化反应性能的影响

通过调控合成方式、改变原料比例,制备纳米棒状、纳米球状、椭球状、圆柱状及棋子状等不同形貌及硅铝比的ZSM-5分子筛,并对其催化甲缩醛气相羰基化反应性能进行详细考察。在110℃、0.6 MPa、CO与甲缩醛流速分别为100 mL·min-1和0.035 mL·min-1条件下,硅铝物质的量比为30的棋子形ZSM-5分子筛表现出最佳的催化活性,甲缩醛转化率达31.9%,目标产物甲氧基乙酸甲脂选择性为21.4%。通过XRD、SEM、XRF、Py-FTIR、NH 3-TPD以及27 Al MAS NMR等对合成的分子筛进行详细表征,发现调控分子筛形貌及硅铝物质的量比可改变ZSM-5分子筛的酸性特征,并改变分子筛骨架中活性铝物种分布。适量的中强B酸酸位及分子筛交叉孔道内较高比例的活性铝物种分布可能是硅铝物质的量比30的棋子形ZSM-5分子筛表现出较好催化活性的原因。

Effect of morphology and Si/Al ratio of ZSM-5 on gas phase carbonylation of dimethoxymethane

A series of ZSM-5 zeolites with different morphologies and Si/Al ratios,including nanorods,nanospheres,ellipsoid-like,column-like and chess-like,were prepared by regulating the synthetic methods and changing the proportion of raw materials.Then their catalytic performance in the vapor-phase carbonylation of dimethoxymethane(DMM) to synthesize methyl methoxyacetate(MMAc) was investigated in this work.The results indicated that chess-like ZSM-5 with a Si/Al ratio of 30 exhibited better performance,the conversion of DMM over which reached 31.9% with a selectivity of 21.4% to MMAc under a flow rate of 100 mL·min^-1 of CO and 0.035 mL·min^-1 of DMM at 110 ℃ and 0.6 MPa.Various characterization techniques were carried out,such as XRD,SEM,XRF,NH₃-TPD,Py-FTIR and ²⁷Al MAS NMR.It was found that the morphology and the Si/Al ratio of the zeolites could adjust the acidic characteristics of ZSM-5 zeolite and change the distribution of active aluminum species in zeolite framework.The suitable medium-strong Brönsted acid sites and the higher proportion of active aluminum species distribution in the intersection of ZSM-5 zeolites might contribute to the higher activity of chess-like ZSM-5 with a Si/Al ratio of 30 in the vapor-phase carbonylation of DMM.