Effects of Promoter La2O3 and Supports on Kinetic Parameters of Dissociation Activation of Methane over Ni-Based Catalysts

The influence of MgAl2O4 and α-Al2O3 supports, and La2O3 promoter on the methane dissociation was studied by pulsing methane over catalysts Ni/α-Al2O3 (A), Ni/La2O3/α-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 methane dissociation on the fresh Ni active sites was disclosed. Kinetic parameters for the methane dissociation over these catalysts were obtained under reaction conditions free from heat and mass transfer limitations. The methane 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 methane dissociation. There is a compensation effect between the activation energy and the pre-exponential factor in the methane dissociation on the Ni-based catalysts, which reduces the influence of the supports and promoter on the methane dissociation.