▎ 摘　　要

Large-scale synthesis and applications of graphene-encapsulated metal catalysts remain a great challenge since it is difficult to control the thickness of graphene layers. In this study, graphene-encapsulated Ni nanoparticles (Ni@Gr) were fabricated via in-situ growth method. Steam-assisted control was carried out to decrease the graphene layer number. The layer-controlled Ni@Gr catalyst consisted of Ni core and graphene shell. The anchored metal was well defended against oxidation or acid etching. In addition, the influence of steam-gasification temperature on the nature of catalysts was also investigated. The catalyst obtained via steam-assisted control at 800 degrees C (Ni@Gr800) possessed excellent textural features, such as thinner graphene shell, more defects on the surface. Consequently, Ni@Gr800 catalyst presented superior initial activity and durability in the steam reforming of ethanol, especially at 550 degrees C. By density functional theory calculations, the presence of defects improved the adsorption energy of all reaction species. The carbonaceous deposition was the primary reason for catalyst deactivation. Textural features of Ni@Gr800 contributed to the formation of carbon filaments, which facilitated coke gasification on the catalyst. This work provides a procedure for controlling the graphene layer number of catalysts with graphene as the covering, and an approach to fabricate defects on the graphene surface. (C) 2019 Elsevier Ltd. All rights reserved.