Sb2O3与HZSM-5的相互作用

研究了氮气气氛下于500℃处理2h后的Sb₂O₃/HZSM-5体系中Sb₂O₃在分子筛表面上的分散行为.发现处理后的体系中Sb₂O₃晶相消失,HZSM-5晶相减少,非晶相增加.经XRD相定量、氮气吸附、正己烷吸附及NH₃-TPD实验可知,高温下酸性Sb₂O₃破坏了分子筛的部分骨架,生成无定形硅铝胶,同时Sb₂O₃高分散在其中.含Sb₂O₃的无定形硅铝胶修饰了分子筛表面,减小了孔口,提高了分子筛在甲苯烷基化反应中的择形性能,对二甲苯的选择性可高达89.

The Interaction Between Sb2O3 and HZSM-5

The behavior of Sb\-2O\-3 on HZSM\|5 was investigated by employing the techniques such as XRD, N\-2 and \%n\%\|hexane adsorption, NH\-3\|TPD etc.. Mechanic mixture of Sb\-2O\-3 and HZSM\|5 was calcined at 500 under nitrogen for two hours. XRD results showed that crystalline Sb\-2O\-3 disappeared while HZSM\|5 framework suffered a noteworthy damage.Quantitative phase analysis indicate that the crystalline HZSM\|5 amount in Sb\-2O\-3/HZSM\|5 shrank from 76% to 59% after calcination. The Sb\-2O\-3/HZSM\|5 to HZSM\|5 ratios of pore volumes (derived from N\-2 adsorption experiment) and \%n\%\|hexane saturated adsorption amount were 060 and 062, both corresponding to that ratio of the crystalline HZSM\|5 amount(059/095=062). The fact suggests that in calcined Sb\-2O\-3/HZSM\|5, nothing exists in the channels of the zeolite. Moreover, it is also found that the \%n\%\|hexane saturated adsorption pressure of Sb\-2O\-3/HZSM\|5 is greater than that of HZSM\|5. Based on the results above, a new mechanism of the interaction between Sb\-2O\-3 and HZSM\|5 was proposed. During calcination, the framework of HZSM\|5 is partly broken by acidic Sb\-2O\-3, which in turn highly disperses into the silica\|alumina gel yielded from framework collapse. This gel modifies the external\|surface of HZSM\|5 by diminishing its pore openings, subsequently enhancing the shape\|selectivity of the zeolite. Toluene alkylation reaction was applied to characterize Sb\-2O\-3/HZSM\|5, the \%para\%\|selectivity attained as high as 89%.