CO methanation as alternative refinement process for CO abatement in H 2-rich gas for PEM applications

Theoretically, there are several methods that can be used to remove CO from H2-rich gases. As for the applications of PEM-FCs to vehicles, boats and yachts and residential co-generators, however, the feasible choice may be only between the preferential CO oxidation (CO-PROX) and the selective CO methanation (COSMET) because of the limited available spaces and low operating pressures in such application systems. The CO-PROX process has so far been extensively tested since it is somehow reliable to remove CO down to 10 ppmv by raising the O2 consumption unlimitedly. Nonetheless, the technology requires a closely controlled low O2 supply to keep the possibly lowest H2 parallel oxidation and a working temperature window suitably wide for control purposes. This, while making the method costly and complicated, obviously hampers its application to low-power PEM-FCs where very small oxidant flows have to be provided by use of well-refined expensive flow meters, such as mass flow meters. Without any additional reactant required, the CO-SMET can avoid the above-mentioned shortcomings of the CO-PROX application. Furthermore, the CO methanation is less exothermic than the CO and H2 oxidations. Thus, a CO-SMET reactor is inherently more easily controllable than a CO-PROX one. The present work deals with a screening of catalysts for CO abatement via selective methanation. Ru-based catalysts supported on TiO2, ZrO2 and CeO2 were prepared by a conventional impregnation method and CO removal was determined by varying the operating conditions. The obtained results showed good performances of the Ru/ZrO2 and Ru/CeO2 supported catalysts, and also the feasibility and applicability of the COSMET process, especially by employing the Ru/CeO2 supported catalyst.