The catalytic activity of well-defined gold nanorods enclosed by Au(111) and Au(100) surfaces is investigated for the Sonogashira cross-coupling reaction between phenylacetylene and 4-iodoanisole, which gives rise to two homo-coupling products (diphenyldiacetylene, PhC C-C Ph and 4,4'-dimethox y-1,1'-biphenyl, MeOC6H4-C6H4OMe) and a cross-coupling product (1-methoxy-4-(2-phenylethynyl)ben zene, Ph CC6H4OMe). This study shows that shorter nanorods (similar to 33 nm) with a higher percentage of Au(111) surface are considerably more selective toward the cross-coupling product (57% conversion with 90% selectivity). The selectivity of longer nanorods (e.g., 42 and 50 nm) with a higher percentage of Au(100) surface, as well as of corresponding shapeless gold nanoparticles (e.g., 2-4 and 20 nm), is found to be less than 59%. The catalytic mechanism of the homo- and cross-coupling reactions, in particular, roles played by Au(100) and Au(111) surfaces, is examined via OFT simulation. It is found that iodobenzene adsorption, C-I bond dissociation, reactant surface diffusion, and coupling reactions are more favorable on Au(111) than on Au(100). This work demonstrates the gold facet effect on catalytic coupling reactions, and the combined approach of experiment and theory permits mechanistic understanding at the molecular level. (C) 2015 Elsevier Inc. All rights reserved.