Pure hydrogen and carbon nanotube production from methane decomposition over hydrotalcite-derived NiMCrAl (M = Co, Cu, Zn) catalysts

Abstract

The catalytic decomposition of CH₄ offers a promising route to obtain pure H₂, which is significant for mitigating greenhouse gas emissions and enhancing methane utilisation. Nickel-based catalysts are the most prevalent for methane cracking. However, catalyst deactivation can occur due to coking and sintering. Therefore, stabilising the active sites of Ni-based catalysts by enhancing metal–support interactions is essential for designing methane cracking catalytic systems. This study investigates the effects of adding Co, Cu and Zn on the performance of a hydrotalcite-derived NiCrAl catalyst. The results showed that Cu increased the specific surface area, decreased the electron density around Ni atoms, facilitated the reduction of NiO, and produced strong interactions between the metal and support. This improved methane decomposition at the Ni active sites and enhanced catalytic stability. The strong interaction between the metal and support suppressed nickel sintering during methane cracking. The Ni_2.4Cu_0.3Cr_0.3Al catalyst retained 50% H₂ yield for 400 min at 650 °C. Online mass spectrometry analysis demonstrated that the catalyst did not generate CO and CO₂ during the methane cracking reaction. XRD and TEM results showed that Cu maintained the balance between CH₄ dissociation and carbon diffusion by stabilising the size of nickel, promoting the transition of deposited carbon from carbon particles to carbon nanotubes. This work provides a reference for designing high-performance nickel-based catalysts for methane cracking.