Highly-stable Ni–Zn catalyst on USY zeolite support for low temperature methane pyrolysis.

Zinc-promoted nickel catalysts on Ultra-Stable Y (USY) zeolite support are tested for their efficacy towards methane pyrolysis. The un-promoted catalyst obtained a conversion of 65.8%, which dropped to 57.3% at the end of the experiment. However, addition of 5 wt% Zn promoter increased the conversion to 67.7%, with no discernible loss in activity after 60 h on-stream. XPS analysis indicated evidence of electronic interaction between the Ni and Zn metals, and the addition of Zn caused a reduction in the metal-support interactions of the catalyst as revealed in TPR and XRD analyses. The catalytic activity of the 50Ni–5Zn/USY also remained completely stable for 60 h even after the operating temperature was increased to 650 °C and the partial pressure of methane in the inlet increased to 80%, at a High gas hour space velocity of 120 L/gcat.h. Analysis of the spent 50Ni–5Zn/USY catalyst revealed the presence of Ni–Zn carbides that may have contributed to the increase in activity, as well as the formation of large quantities of highly graphitic and ordered multi-walled carbon nanotubes produced by the tip-growth mechanism which have been shown to prolong catalyst lifetime on-stream. • Electronic interactions between Ni and Zn enhanced catalytic activity. • Zinc catalyst doping weakened metal-support interaction and increased NiO particle size. • 5% zinc loading raised methane conversion to 67.7% which remained stable for 60 h. • Addition of Zn increased the degree of carbon graphitization. • The observed tip growth carbon mechanism improved catalyst stability. [ABSTRACT FROM AUTHOR]