CH_4在Ni-Mg-O催化剂上裂解生长碳纳米管的本征动力学

Intrinsic Kinetics of Pyrolysis of CH_4 to Grow CNTs over a Ni-Mg-O Catalyst

考察甲烷在Ni0.5Mg0.5O催化剂上裂解生长碳纳米管(CNT)的本征动力学.在常压,540～640℃,GHSV=(2.0～9.0)×104mLh-1g catal-1.反应条件下,测得甲烷裂解转化率随反应温度、接触时间的变化,运用最小二乘法拟合求算出反应速率,进而建立反应动力学方程的幂函数模型,求得甲烷和氢气的反应级数分别为1.32和-1.41,反应活化能Ea为172kJmol-1,并根据实验数据验证了甲烷在Ni基催化剂上吸附、解离、脱氢的机理模型.

Reaction kinetics of catalytic pyrolysis of methane over nickel-based catalysts has been extensively studied. Over a quarter of the century, many efforts were being directed at preventing from deactivation of catalyst due to carbon deposit accumulation in many processes involving methane conversion reactions, while the kinetic study aimed at the catalytic pyrolysis of methane to grow carbon nanotubes has been few and far between in literature. In the present work, the intrinsic kinetics of methane pyrolysis to grow carbon nanotubes on a Ni-Mg-O catalyst was investigated. Under the reaction condition of 0.1 MPa, 540～640 ℃, GHSV = (2.0～9.0) ×10~4 mL (STP) h^(-1)g-catal.^(-1),changes of methane conversion with reaction temperature and contact time were measured. By using least square method, the reaction rate was calculated, and a model of powder function for the reaction-kinetic equation was established, and through calculations based upon this equation, it was acquired that the reaction order of CH_4 and H_2 was 1.32 and -1.41 respectively, and the activation energy Ea was 172 kJ mol^(-1). The results of the present investigation provide experimental evidence in supporting the mechanism and kinetic model of dissociative chemisorption followed by successive dehydrogenation of methane, with the first step of dehydrogenation as the rate-determining step, on the Ni-Mg-O catalyst.