Infrared Evidence of a Formate-Intermediate Mechanism over Ca-Modified Supports in Low-Temperature Ethanol Steam Reforming

An in situ DRIFTS study of ethanol adsorption and desorption was performed on Pt (Rh, Pd) supported on Al2O3 and Ca-Al2O3. Different from the well-known acetate-intermediate reaction mechanism observed on Al2O3-supported metal catalysts, formate species are exclusively observed on Pt (Rh, Pd) supported on Ca-Al2O3, offering a new mechanism denoted as the formate-intermediate mechanism. The key factor in determining the change in mechanism is the reduced availability of surface oxygen and the enhanced C–C breaking ability of the metal catalyst upon Ca modification. The formate-intermediate mechanism is favored in the presence of noble metals in the following order: Pt > Rh > Pd.