Reinforcing hydrogen and carbon nanotube co-production via Cr–O–Ni catalyzed methane decomposition

Abstract

Catalytic methane decomposition shows the prominent superiority of generating hydrogen in one step with almost no carbon oxide production; however, it suffers from catalyst deactivation and low by-product carbon quality. Herein, a series of H₂-reduced Ni_xCr₂O_x+3 (abbreviated as reduced Ni_xCr₂) catalysts were designed and synthesised for highly efficient methane decomposition and carbon nanotube production. A maximum methane conversion of 87.1% and hydrogen concentration of 91.8 vol% were achieved at 750 °C without deactivation. The results from XPS, XAS, and Raman reveal that the reduced Ni_xCr₂ catalysts have significant activity and stability. On the one hand, they form the Cr–O–Ni structure, thus possessing strong Ni–Cr₂O₃ interaction. On the other hand, the lattice oxygen of the reduced Ni_xCr₂ catalysts induces methane activation, thus accelerating methane activation, as demonstrated by the generation of a little amount of CO. In addition, the relationship between the types of carbon deposited and Ni/Cr ratio, decomposition temperature, and time was also revealed to guide carbon nanotube synthesis. Density functional theory calculation confirms the lowest dehydrogenation barrier of Ni(111)/Cr₂O₃(012), demonstrating the superiority of the Cr–O–Ni catalyzed methane decomposition. These findings provide innovative ideas for the construction of functionalized materials, which will substantially promote the development of methane decomposition.