AbstractWe present the results of an NMR investigation to study the decomposition of acetylene adsorbed on small Pt clusters similar to industrial catalysts. We begin by reviewing some of our earlier results where it was shown that acetylene converts primarily to vinylidene (CCH2) upon room temperature adsorption. It was proposed that the vinylidene gradually dehydrogenates between 450 and 650 K leaving C2surface species whose carbon‐carbon bond breaks at about 670 K. In this work we have shown that ethylidyne (CCH3) plays an important role in providing an alternate decomposition mechanism. In addition, although there is some evidence that CCH surface species are formed upon room temperature adsorption, no C2surface species were observed in our experiments. Therefore, although dehydrogenation prior to carbon‐carbon bond scission may occur, further experiments where the ethylidyne mechanism is eliminated are needed to completely unravel the decomposition mechan