The selective hydrogenation of p-chloronitrobenzene on Au-13 and Au-55 nanoclusters has been systematically studied by density functional theory (DFT), allowing for a comparison with Au-20 nanocluster. All possible adsorption configurations of relevant intermediates are identified. The adsorption energy of all species exhibit the following trend: Au-13 > Au-20 > Au-55. The detailed reaction barriers show that Au-55 nanocluster has the least hydrogenation reaction barrier of the rate-limiting step, whereas the dechlorination reaction is least likely to cause on Au-55 nanocluster. These observations suggest that the 55-atom gold cluster is predicated to be the appropriate catalyst for practical application. (C) 2018 Elsevier B.V. All rights reserved.