KINETICS FOR CO PREFERENTIAL OXIDATION (COPROX) OVER CUO/CEO2 CATALYSTS

FERNANDO MARIÑO; MÁXIMO MORENO; GRACIELA BARONETTI; MIGUEL LABORDE

Bilbao, España

Conferencia; Chemical Reaction Engineering XI - Green Chemical Reactor Engineering; 2007

The hydrogen-rich gas mixture obtained by partial oxidation or steam reforming of a hydrocarbon or alcohol source usually contains 10000-20000 ppm of CO even after water-gas shift reaction takes place. Unfortunately, the presence of this amount of CO in the gas mixture causes the performance of the fuel cells to rapidly deteriorate due to poisoning of the Pt-containing anode electrode. Therefore, hydrogen obtained from hydrocarbons or alcohols must be purified before entering the PEMFC. The preferential oxidation of CO (COPROX) is the simplest and the least expensive ultimate purification technique. In this work, kinetic studies of CO oxidation in excess of H2 over CuO/CeO2 catalyst have been performed. Residence time was adjusted to obtain conversions lower than 10% in order to work under differential reactor conditions. Reaction temperature was varied between 120ºC and 200ºC and partial pressures of CO, O2 and CO2 were varied between 0.008 and 0.10 bar. In all experiences, H2 partial pressure was fixed at 0.6 bar and N2 was used as balance; total pressure was kept at 1 bar. The adjusted kinetic parameters were partial order of reaction with respect to CO, O2 and CO2, and the apparent activation energy. Partial order of reaction with respect to CO was found to be nearly one (0.8) and reaction rate has shown to be virtually independent of O2 partial pressure. In the case of the activation energy, two temperature regions were observed: between 120ºC and 150ºC, the value of Ea was 68.2 kJ/mol; and, in the range 150-200ºC, Ea was found to be 29.1 kJ/mol. The effect of the water content in the inlet stream was analyzed using light off curves for different PH2O. The results indicate that the presence of water does have an appreciable negative effect, but this effect being almost independent of water partial pressure.