Insight into the role of metal/oxide interaction and Ni availabilities on NiAl mixed metal oxide catalysts for methane decomposition

Ni loaded mixed metal oxides (MMO) catalysts were systematically synthesized with different Ni/Al ratios through layered double hydroxides (LDH) decomposition, fully characterized using various techniques, and tested in catalytic methane decomposition reaction to study the properties of active nickel species on supports. H-2 chemisorption indicated the Ni metallic surface areas on Ni0.5Al-MMO and Ni1Al-MMO were 17.1 and 21.1 m(2)/g, respectively, which were much higher than those on Ni-0.5/Al2O2 and Ni-1/Al2O3 impregnated catalysts (at 8.8 and 8.5 m(2)/g, respectively). However, the MMO catalysts gave the lower carbon nanotubes (CNTs) yield compared with the impregnated catalysts. Form the XPS, XRD and H-2-TPR characterizations, it were found that there existed a strong metal and support interaction, leading to less NiO being reduced as the active sites. When Ni/Al ratios increased to 2 and 3, the CNT yields for the NixAl-MMO catalysts were much higher than those of impregnated Ni catalysts, up to 2.02 g(c)/g(cat). and 4.55 g(c)/g(cat), vs 1.36 g(c)/g(cat) and 1.29 g(c)/g(cat), respectively. From H-2 chemisorption, we found that NixAl-MMO (x = 2 or 3) catalysts had much higher metallic surface areas (22.3 m(2)/g and 24.6 m(2)/g), while they were only 4.9 m(2)/g and 4.3 m(2)/g on the impregnated catalysts at the same Ni loadings. It suggests MMO catalysts have more reduced Ni active sites available for methane decomposition reaction, attributing to the proper metal-support interactions. SEM and TEM results display the uniform Ni particle sizes existing on MMO catalysts, giving a nice correlation to the inner diameter of CNTs produced.