Effects of promoter La2O3 and supports on kinetic parameters of dissociation activation of CH4 over ni-based catalysts

The influence of MgAl2O4 and alpha-Al2O3 supports, and La2O3 promoter on the CH4 dissociation was studied by pulsing CH4 over catalysts Ni/alpha-Al2O3 (A), Ni/La2O3/alpha-Al2O3 (A-L), Ni/MgAl2O4 (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 (E.) on catalysts A, A-L, M, and M-L is 90.9, 111.8, 79.5, and 85.9 kJ/mol, respectively. The E-a values on catalysts M and M-L are lower than those on catalysts A and A-L. The La2O3 promoter increases the E. of CH4 dissociation. There is a compensation effect between the activation energy and the pre-exponential factor in the CH4 dissociation on the Ni-based catalysts, which reduces the influence of the supports and promoter on the CH4 dissociation.