Abstract The decomposition of adsorbed acetate groups on a 1% Rh/Al 2O 3catalyst has been investigated by means of temperature-programmed desorption (TPD) at atmospheric pressure, in a microreactor fitted with an on-line mass spectrometer. Under certain conditions of catalyst pretreatment, the adsorbed acetate groups decompose autocatalytically in a process that has been described in the past as a “surface explosion.” The phenomenon of surface explosions has been investigated by various groups and was generally considered to be confined to ultrahigh vacuum regimes using single crystals. It is found, however, that the explosive acetate decomposition reaction actually translates directly to real supported metal catalysts at atmospheric pressure. A description is given involving the influence of adsorbed oxygen and differentiated acetate adsorption sites on the metal, the support, and at the interface between the two. Surface migration of the acetate groups is also involved in determining the intensities of the various TPD peaks.