Adsorption, polymerization and decomposition of acetaldehyde on clean and carbon-covered Rh(111) surfaces

•The adsorption form of acetaldehyde vary drastically by exposure on Rh(111).•At higher exposure polymerization processes occurred on the surface.•Desorption of trimers were also evidenced by TPD.•Surface carbon decreases the uptake of adsorbed acetaldehyde.•Carbon reduces the formation of polymers and induces the CO bond scission.