Thermocatalytic decomposition of methane is proposed to be an economical and green method to produce COx-free hydrogen and carbon nanomaterial. In present work, 60 wt% Ni/Al2O3 catalysts with different additives (Cu, Mn, Pd, Co, Zn, Fe, Mg) were prepared by co-impregnation method to investigate promotional effects of these metal additives on the activity and stability of 60 wt% Ni/Al2O3 and find out a really effective promoter for decomposition of methane. The catalyst was characterized by N-2 adsorption/desorption, X-ray diffraction, scanning electron microscopy, inductively coupled plasma optical emission spectrometer and hydrogen temperature programmed reduction. While metal additives (5 wt%) were added into 60 wt% Ni/Al2O3, the activity stability of 60 wt% Ni/Al2O3 was improved and the CH4 conversion of 60 wt% Ni/Al2O3 was also improved except Zn addition. Mn addition was found to improve the catalytic activity of 60 wt% Ni/Al2O3 significantly and the CH4 conversion of 5 wt% Mn-60 wt% Ni/Al2O3 was -80%. Cu addition was found to remarkably improve the catalytic stability of 60 wt% Ni/Al2O3 and the CH4 conversion of 5 wt% Cu-60 wt% Ni/Al2O3 decreased from 61% to 45% after 250 min of reaction time. Carbon nanomaterials formed in the thermocatalytic decomposition process were characterized by X-ray diffraction, scanning electron microscopy, thermal gravimetric analyzer and Raman spectroscopy. Carbon deposits consist of amorphous carbon and carbon nanofibers. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.