W掺杂对Mo/HZSM-5催化甲烷无氧芳构化性能的影响

采用浸渍法制备了Mo/HZSM-5、Mo-W/HZSM-5和W/HZSM-5三种催化剂。通过XRD、BET、Py-FTIR、H2-TPR、XPS、TEM、NH3-TPD、TPO、TG和Raman等技术对催化剂的物化性质进行表征,并考察其在甲烷无氧芳构化反应中的催化性能。结果表明,相比于Mo/HZSM-5,Mo-W/HZSM-5催化剂表现出更高的CH_4转化率、芳烃收率以及催化稳定性。H_2-TPR和XPS结果表明,Mo-W/HZSM-5中存在更易被还原为W~(4+)的正八面体(WO_6)~(n-)前驱体,反应过程中W4+的形成有助于提高CH_4转化率。同时,积炭表征结果表明,石墨型积炭是导致Mo/HZSM-5催化剂快速失活的主要原因,W掺杂可以抑制MoW/HZSM-5催化剂上石墨型积炭的形成,进而提高催化剂的稳定性。

Effect of W addition on the catalytic properties of Mo/HZSM-5 catalyst in methane non-oxidative dehydroaromatization

Mo/HZSM-5,Mo-W/HZSM-5 and W/HZSM-5 catalysts were prepared via a conventional impregnation method. The catalysts were characterized by means of XRD, BET, Py-FTIR, H₂-TPR, XPS, TEM, NH₃-TPD, TPO, TG and Raman,and were evaluated in methane non-oxidative dehydroaromatization(MDA). Compared with Mo/HZSM-5,the CH₄ conversion,aromatics yield and catalytic stability were improved by W addition for Mo-W/HZSM-5 in MDA reaction. H₂-TPR and XPS results indicated that the octahedral (WO₆)^n- groups existed in Mo-W/HZSM-5 were more easily reduced to W⁴⁺-containing species in MDA reaction in comparison with W/HZSM-5, and W⁴⁺-containing species was correlated with the high MDA activity. At the same time, it is found that graphitic-like coking is the main reason of catalyst deactivation for Mo/HZSM-5, and this coking over Mo-W/HZSM-5 catalyst can be inhibited by W addition during MDA.