摘要
通过非稳态脉冲动力学方法,考察了载体MgAl2O4和α-Al2O3以及助剂La2O3对Ni催化剂催化解离CH4性能的影响.在以前的积炭方法中,CH4的解离在很大程度上受积炭的影响.这里采用非稳态脉冲方法可以得到在新鲜的Ni活性位上CH4解离的本征动力学信息.在排除了传质和传热的影响之后考察了在Ni/α-Al2O3,Ni/La2O3/α-Al2O3,Ni/MgAl2O4和Ni/La2O3/MgAl2O4催化剂上的CH4解离动力学,求得催化剂表面上平均每个Ni活性位上CH4解离的活化能分别为90·9,111·8,79·5和85·9kJ/mol.可以看出,载体MgAl2O4比α-Al2O3更能降低Ni上CH4解离的活化能,而La2O3的加入会提高CH4在Ni上的解离活化能.通过动力学方法,定量地描述了载体和助剂对Ni活性位上CH4解离能力的影响.同时CH4解离的活化能和指前因子之间存在着补偿效应,这在一定程度上削弱了助剂和载体对Ni上CH4解离的影响.
The influence of MgAl2O4 and a-Al2O3 studied by pulsing CH4 over catalysts Ni/a-Al2O3 supports, and La2O3 promoter on the CH4 dissociation was （A）, Ni/LazO3/a-Al2O3 （A-L）, Ni/MgAI204 （M）, and Ni/La2O3/MgAl2O4 （M-L）. In these unsteady pulse reactions, the carbon species coverage on the catalysts was kept less than 100 % and the information about CH4 dissociation on the fresh Ni active sites was disclosed. Kinetic parameters for the CH4 dissociation over these catalysts were obtained under reaction conditions free from heat and mass transfer limitations. The CH4 dissociation activation energy （Ea） on catalysts A, A-L, M, and M-L is 90.9, 111.8, 79.5, and 85.9 kJ/mol, respectively. The Ea values on catalysts M and M-L are lower than those on catalysts A and A-L. The La2O3 promoter increases the Ea of CH4 dissociation. There is a compensation effect between the activation energy and the pre-exponential factor in the CH4 dissociation on the Nibased catalysts, which reduces the influence of the supports and promoter on the CH4 dissociation.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2006年第6期479-484,共6页
关键词
甲烷
解离
镍基催化剂
氧化镧
活化能
指前因子
methane
dissociation
nickel-based catalyst
lanthana
activation energy
pre-exponential factor
