Infrared and molecular beam experiments are used to compare and contrast the adsorption and reaction of NO and trans-1,2-dichloroethene on Cu(110) and on Cu nanoclusters deposited on a 5 Å thick Al₂O₃ film. The overall reaction of NO, leading to decomposition, is almost identical in the two systems, with both types of Cu surfaces promoting the formation of NO dimers, which are precursors to the dissociation products N₂O, N₂ and O. Although the overall reaction is independent of surface structure, the IR spectra clearly show differences in the adsorption sites occupied on the single crystal and the clusters, a disparity that is also shown by CO adsorption experiments. In contrast, the reaction pathway of dichloroethene does show differences on the two types of Cu surfaces. On both surfaces, the initial reaction step is insensitive to structure and efficient dechlorination leads to the production of adsorbed acetylene. However, the fate of this intermediate depends critically on the underlying surface. On Cu(110), the acetylene trimerises readily into benzene at 350 K. However, this reaction shows a significant size dependent behaviour on the supported nanocluster systems, with the probability for trimerisation diminishing with decreasing cluster size.