Synthesis of chemically stable non-precious-metal 3d-block transition metal nanocatalysts for catalytic syngas conversion remains a great challenge, since the nanocatalysts are usually too active to remain stable under ambient conditions. In situ grown (N-doped) graphene-encapsulated Ni nanoparticles (NPs) (Ni@G, Ni@G-N) were successfully obtained by a simple route via an arc-discharge method. The Ni@G composite is composed of a graphene sheath and a metallic nickel core. The carbon layer can prevent the inner Ni NPs from being etched when they are exposed to air, H2O2 or acid. Moreover, the as-prepared Ni@G exhibit excellent catalytic activity and methane selectivity and high stability in the methanation reaction. The catalytic performance can be further improved by doping nitrogen into the graphene shell. This method provides a good procedure for graphene encapsulation of non-precious-metal nanoparticles. (C) 2015 Elsevier Inc. All rights reserved.