Thermal decomposition of benzene on the Rh(111) crystal surface

Benzene decomposition on the Rh(111) crystal surface has been studied over the temperature range of 300-800 K by high-resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED). Our results show that benzene decomposition begins at 400 K, forming a mixture of CH and C₂H species. The relative amounts of these two species vary with temperature; at 470 K, the concentration ratio of CH to C₂H is 0.4. Above 500 K, these fragments dehydrogenate and condense to form C_nH polymers. By 800 K, the adsorbed monolayer is completely dehydrogenated, forming a polymeric carbon monolayer with a vibrational spectrum similar to that of an ordered graphite monolayer. We propose that benzene decomposition on Rh(111) proceeds by decyclotrimerization to form three acetylenes which immediately decompose to CH and C₂H species.