Activity of rhodium-based catalysts for CO preferential oxidation in H2-rich gases

The CO preferential oxidation (CO-PROX) process can lead to a reduction of the CO concentration in the hydrogen-rich gas from WGS process of hydrocarbons reformate down to at least 10 ppmv or below, so as to enable its direct feeding to standard PEM fuel cells. Rh-based catalysts supported on 3A zeolite, alumina, titania or ceria were prepared and tested for potential application in CO-PROX operating in a temperature range compatible with PEM FCs (80-100 degrees C). Among the prepared catalysts, 1% Rh-3A zeolite catalyst was found to be the most suitable one for the CO-PROX at low temperature: it reduced the inlet CO concentration below 10 ppmv within a temperature range of at least 80-120 degrees C without the appearance of undesirable side reactions. In order to improve the oxygen selectivity toward the CO complete oxidation with a lowest as possible hydrogen parasitic oxidation, the oxygen amount in the feed gas composition was decreased. With 1% Rh-3A zeolite catalyst the lowest O-2 feed concentration was found to be 3 times the corresponding value of the CO stoichiometric oxidation (lambda = 2O(2)/CO = 3). Finally, with the goal to reduce the noble metal costs, tests at lower Rh load (from 1 to 0.5%) were carried out. No significant variations in both activity and width of complete CO conversion temperature range resulted for 0.5% Rh-3A catalyst. Therefore, this catalyst operating at lambda = 3 could potentially be used for the CO-PROX reaction at low temperature.