On the mechanism of CO and CO2 hydrogenation reactions on zirconia-supported catalysts: a diffuse reflectance FTIR study: Part I. Identification of surface species and methanation reactions on palladium/zirconia catalysts

摘要: Abstract Hydrogenation reactions over zirconia-supported palladium catalysts have been investigated by diffuse reflectance FTIR spectroscopy. Catalysts obtained activation of an amorphous Pd 25 Zr 75 precursor, as well prepared wet impregnation zirconia, were characterized in flowing CO/H 2 or CO /H reactant gases, respectively, the temperature range 298–473 K. In addition, species present on catalyst surface under equilibrated conditions studied static system, after gas flow was terminated. Supplementary information studying occurring when first exposed to reaction conditions, and subsequently a stream pure hydrogen. Surface identified comparison with adsorption studies which loaded reference compounds (CO , formaldehyde, methanol methanol-d 4 ), spectrum recorded function temperature. Upon exposure rapid formation formate observed. Similarly, rapidly transformed upon initial onto activated catalysts. The disappearance formate, observed spectrum, could be correlated appearance phase methane. A second major route reactions, proceeds from mixtures, involves adsorbed CO, π-bonded surface-bound methylate, product. Interestingly, there no observable correlation between formaldehyde methylate one hand, methane other hand. steps involved zirconia palladium/zirconia are discussed detail, relevant mechanism.