The density functional theory (DFT) was adopted to study the adsorption and growth of Ru-n (n = 1-4) clusters on gamma-Al2O3 surface, which is of great significances for the design of many important catalysts, especially for carbon dioxide methanation. It is found that both the Ru-Ru bond length and adsorption energy E-ads of Ru clusters with the surface increase with the Ru-n clusters increasing. The growth ability of the supported Ru-n cluster is weaker than the gas phase Ru-n clusters through comparing their respective growth process, which ascribes to the stabilization of gamma-Al2O3 support. An interesting discovery is that the basin structure was supposed to be the most favorable adsorption geometry for Run clusters. Additionally, the distances between Ru atoms in the adsorbed clusters are longer than that in their isolated counterparts. Bader charge analysis was conducted for the most stable configurations of Ru-n (n = 14) clusters on gamma-Al2O3 surface as well. And the results suggest that Ru-n (n = 1-4) clusters serve as the electron donators. The result of projected density of states (PDOS) shows that strong adsorption of Ru atom on the gamma-Al2O3 surface correlates with strong interaction between d orbital of Ru atom and p orbital of Al or O atom of the Al2O3 support. (C) 2018 Elsevier B.V. All rights reserved.