阶跃过渡应答技术研究Mo-V/Al_2O_3催化剂上乙烷氧化脱氢制乙烯反应的暂态动力学 Ⅱ.乙烷氧化脱氢反应的机理和动力学参数的求取

STUDY OF TRANSIENT KINETICS OF OXYDEHYDROGENATION OF ETHANE TO ETHYLENE OVER Mo-V/Al_2O_3 BY STEP TRANSIENT RESPONSE TECHNIQUE Ⅱ.MECHANISM OF OXYDEHYDROGENATION OF ETHANE TO ETHYLENE AND EVALUATION OF KINETIC PARAMETERS

通过一系列应答实验,证实了氧在MoO_3-V_2O_3催化剂上的吸附和吸附态氧转变为晶格氧的过程是慢过程,是乙烷氧化脱氢反应的速度控制步骤;乙烯的深度氧化是乙烯与催化剂表面上吸附态氧作用的结果,而不是与催化剂上晶格氧作用的结果。结合第Ⅰ部分的实验结果,提出了乙烷氧化脱氢制乙烯反应的机理,并用Treanor法和DPP法求取了各基元步骤的速率常数、活化能和指前因子等动力学参数。用计算所得的结果进行拟合,其结果与实验曲线吻合。

The mechanism and the kinetic parameters of oxydehydrogenation of ethane have been studied.The results show that the process of adsorption of O2 on MoO3-V2O5/Al2O3 catalyst surface and the transformation of the adsorbed O species to lattice O are very slow, and they are the rate--control step of oxydehydrogenation of ethane; in the range of 320-450℃, the formation of the surface intermediate by ethane reacting with lattice O, the formation of ethylene by the decomposition of surface intermediate and the desorption of ethylene are fast steps . The oxydehydrogenation of ethane after pre-adsorption of O2 at 500℃ shows that the main reaction, oxydehydrogenation of ethane to ethylene is resulted from ethane reacted with surface lattice O, and the side reaction of deep oxidation of etbylene is caused by the reaction of ethylene with O adsorbed on catalyst surface. The mechanism of the oxydehydrogenation of ethane is suggested and the kinetic parameters of the elementary step are evaluated.