Effect of carbon dioxide and water on the performances of an iron-promoted copper/ceria catalyst for CO preferential oxidation in H2-rich streams

The catalytic behavior of an iron-promoted copper/ceria catalyst towards CO-PROX reaction under feed mixtures containing variable concentrations of CO2 (0-15 vol.%) and H2O (0 -10 vol.%) was compared to that of an unpromoted sample with the same copper loading. At low temperature both species inhibit CO conversion on Fe-promoted catalyst more than on the reference Cu/CeO2 catalyst, although the performance is restored more rapidly to that corresponding to CO2-free conditions by increasing the temperature. CO2 temperature programmed desorption tests were carried out and experimental curves modeled to evaluate quantitatively the active sites for CO and H2 oxidation. Iron addition significantly reduced the amount of H2 oxidation sites, likely promoting copper dispersion, leading to the observed better selectivity under CO2-free conditions. The inhibiting effect of CO2 was ascribed to the formation of quite stable CO2 adsorbed species blocking copper active sites. The different dependence on the temperature of CO2 desorption results in a higher inhibition at low temperature for the Fe-promoted catalyst, but also in an easier CO2 desorption at higher temperature restoring the performance under CO2-free conditions for this sample.