Zn-Al共掺杂La_(2)O_(3)催化剂在甲烷氧化偶联中的性能

Performance of Zn-Al co-doped La_(2)O_(3) catalysts in the oxidative coupling of methane

采用柠檬酸溶胶凝胶法制备了Zn掺杂和Zn-Al共掺杂的La_(2)O_(3)催化剂,运用原位表征技术研究了该催化剂在甲烷氧化偶联(OCM)反应中的构效关系。原位XRD表征结果发现,La_(2)O_(3)晶体在高温下沿c轴发生热膨胀。H2-TPR结果显示,La_(2)O_(3)基催化剂中含有两种类型的氧物种,即强结合氧和弱结合氧;XPS结果表明,强结合氧归属于为O−。Zn掺杂的La_(2)O_(3)催化剂在高温下形成更多的氧空位,能活化氧气产生更多的强结合氧,因而在OCM反应中表现出较好的催化性能。Al的共掺杂能促进Zn在La_(2)O_(3)中的分散,进一步增加强结合氧数量,提升OCM反应C_(2+)烃的选择性。

Zn-doped and Zn-Al co-doped La_(2)O_(3)catalysts were prepared by citric acid sol-gel method and characterized by a series of in situ technologies,to investigate the structure-activity relationship of La_(2)O_(3)-based catalysts in the oxidative coupling of methane(OCM).The in situ XRD results reveal a thermal expansion of the La_(2)O_(3)crystal along the c-axis at high temperature.The H2-TPR results show two types of oxygen species on the La_(2)O_(3)-based catalysts,viz.,the strong-binding oxygen species and weak-binding oxygen species;in addition,the XPS results indicate that the strong-binding oxygen species is probably attributed to anion radical O−.The doping with Zn can significantly increase the number of oxygen vacancies in the Zn-doped La_(2)O_(3)catalysts,which can promote the activation of oxygen and generate more strong-binding oxygen species;as a result,the Zn-doped La_(2)O_(3)catalyst shows better performance in OCM in comparison with the unmodified La_(2)O_(3)catalyst.Moreover,the co-doping with Al can promote the dispersion of Zn in La_(2)O_(3)and further raise the number of strong-binding oxygen species in the Zn-Al co-doped La_(2)O_(3)catalysts,which is beneficial to enhance the selectivity to C_(2+)hydrocarbons in the OCM reaction.