Electronic effects of alkaline carbonates in methanation over Pd/Al₂O₃ catalysts

Electronic effects of alkaline carbonates on the C-O bond dissociation of adsorbed CO in methanation over Pd/Al₂O₃ catalysts were investigated by using a pulse surface reaction rate analysis (PSRA) coupled with an emissionless diffuse reflectance infrared spectroscopy (EDR). Alkaline carbonates added to the Pd/Al₂O₃ catalyst exist mainly on the alumina support. This addition causes the IR bands of adsorbed CO to shift to lower frequencies, and markedly decreases the rate constant for the C-O bond dissociation. It was concluded that the addition of alkaline carbonates to the Pd/Al₂O₃ catalyst increases the electron density of the Pd metal which in turn decreases the rate constant for the C-O bond dissociation of adsorbed CO. This relationship was explained in terms of a partially hydrogenated CO species which acts as intermediate for the C-O bond dissociation of adsorbed CO in methanation.