Effect of crystalline structure and pore geometry of silica based supported materials on the catalytic behavior of metallic nickel particles during methane decomposition to COx-free hydrogen and carbon nanomaterials

Abstract

This paper aims to study the effect of crystalline structure and pore geometry of some silica supported materials on the catalytic performance of the active Ni component. Therefore, 40 wt.% Ni loaded ZSM-5(25), ZSM-5(400) and amorphous silica (AS) catalysts were prepared by conventional impregnation method and evaluated as catalysts for methane decomposition to COx-free hydrogen production. Several techniques such as XRD, BET, HRTEM, TPR, TGA and Raman spectroscopy were performed for characterizing the fresh and reacted catalysts. The results revealed that the crystalline structure and pore geometry of the supports play an essential role on the catalytic efficiency in terms of H2 yield and stability as well as on the morphology of as-deposited carbon material. The characterization results showed that the particle size and dispersion of NiO were strongly influenced by the crystalline structure of the support. The channels and cages of both zeolite samples could inhibit the agglomeration of NiO particles during the calcination and catalytic runs. On the other hand, the amorphous structure of SiO2 induced serious aggregation of NiO particles, leading to a remarkable inhibition in the activity. TEM images showed that different types of carbon nanomaterials were obtained on the catalysts depending on the crystalline nature of the support. Filamentous carbon was formed on both Ni/ZSM-5(25) and Ni/ZSM-5(400) catalysts, whereas graphene nanosheets were obtained over Ni/SiO2 catalyst.