The UV (325 nm) photolysis of the Rh-I(CO)(2) species on an Al2O3 support produces an active surface intermediate, Rh-I(CO), which reacts with the C-H bond of cyclohexane by oxidative addition to form a postulated surface species, Rh(CO)(H)(C6H11) This species degrades to form a stable C6H11 species on the surface. Unexpectedly, the normalized yield of surface C6H11 species was found to be higher for lower Rh loadings using the same number of UV photons per unit area. This could be qualitatively explained by the fact that the formation of a dimer surface species, Rh-2(CO)(3) (a competitive reaction for the intermediate, Rh-I(CO), responsible for C-H bond activation), is favored for high surface concentrations of Rh-I(CO)(2). It is shown that the dimer formation competes with the desired C-H bond activation process.