Characterisation of coke obtained over MgO-modified Ni/SiO2 in the decomposition of methane

Abstract

In the present work, the effect of MgO incorporation on the catalytic performance of a conventional 20%Ni/SiO2 catalyst in the direct methane decomposition for COx-free H2 production at an optimum temperature of 600 oC was investigated. A series of MgO modified 20%Ni/SiO2 catalysts of Mgat/Niat ratio of 0.1-2.2 were prepared by the co-impregnation method and the physico-chemical properties characterized using ICP, BET, H2- chemisorption, TPR and XRD. The highest pseudo steady state methane conversions for all the catalysts were in the range of 45-55%. The effect of MgO incorporation in the 20%Ni/SiO2 catalyst on the nature of the coke was also investigated. TEM, TGA, Raman and IR spectroscopy studies on the coke revealed that the MgO had little effect on the nature of the coke. CHNS analysis revealed that high coke yields were obtained with catalysts with an average Ni particle size of 36 nm, high degree of reduction and low MgO content, indicating that Ni catalysed methane decomposition is dependent on the size of Ni particle, the reducibility of the nickel species and perhaps MgO enhanced coke gasification. The unmodified 20%Ni/SiO2 had the best performance in terms of coke capacity (3.0gC/gcat). The optimum ratio of Mgat/Niat in 20%Ni/SiO2 for methane decomposition was 0.1, with a coke capacity of 2.6gC/gcat. Initial attempts to separate the coke from the spent catalyst are also presented.