The low-temperature cyclotrimerization of acetylene to benzene on alumina thin film supported Pd particles of controlled size has been studied by temperature-programmed desorption. The reactively formed benzene is observed to desorb in three distinctly separate features with kinetics resembling those observed for acetylene cyclotrimerization on Pd single crystals. An enhanced activity for low-temperature benzene desorption is observed for the larger Pd particles, consistent with single-crystal results that reveal that the Pd(111) surface favors low-temperature desorption of the reactively formed benzene relative to more open surfaces. Additionally, a pronounced drop-off in benzene production is observed for the smallest particles studied, suggestive of an ensemble size requirement for the reaction.