Fe前驱体离子价态对制备Fe/HZSM-5催化剂的甲烷芳构化催化性能的影响

Impact of the Ion Valence of Fe Precursors on the Catalytic Performance of Methane Aromatization When Preparing Fe/HZSM-5 Catalyst

以二价和三价Fe为Fe前驱体制备铁离子交换Fe/HZSM-5催化剂,采用XRD、UV-vis、H_(2)-TPR、NH_(3)-TPD和STEM等多种手段表征了催化剂中Fe物种分散情况和化学状态,并考察它们对甲烷芳构化反应的性能差异。结果表明:二价Fe离子制得的催化剂中Fe载量要显著高于三价Fe离子制备的催化剂,同时剩余较少的B酸位,抑制烯烃和芳烃进一步脱氢和缩聚。Fe物种与骨架Al作用形成不易还原的铁氧物种可作为甲烷活化的催化中心。虽然三价Fe离子交换制得的催化剂具有类似的铁氧物种结构,但由于过低的Fe载量和过多的B酸位剩余,反应中几乎没有芳烃生成,产物中更多的是积炭。研究表明,适宜的金属载量与分子筛B酸剩余量对反应有着重要的影响。研究结果可为进一步优化合成Fe基分子筛催化剂提供思路。

Fe ion-exchanged Fe/HZSM-5 catalyst was prepared with the divalent and trivalent Fe as Fe precursors.The dispersion and chemical states of Fe species in the catalyst were characterized by XRD,UV-vis,H_(2)-TPR,NH_(3)-TPD and STEM,and the difference in their properties for methane aromatization was investigated.The results show that Fe load in the catalyst prepared by divalent Feions was obviously higher than that prepared by trivalent Fe ions.At the same time,less Brönsted acid sites are remained,which can inhibit the further dehydrogenation and polycondensation of olefins and aromatics.Fe species react with Al skeleton to form the ferrite species that are nonreducible,and can be used as the catalytic center for methane activation.Although the catalyst prepared by trivalent Fe ion exchange has a similar structure with ferrite species,there is nearly no aromatics generated during reaction due to the excessively low Fe load and the remaining excessive Brönsted acid sites,and there are more carbon depositions in the product.The research suggests that an appropriate amount of metal load and zeolite Brönsted acid surplus have an important impact on the reaction.The research results can provide an idea for further optimizing the Fe-based zeolite catalyst.