CO Methanation Over Ru-Al2O3 Catalysts: Effects of Chloride Doping on Reaction Activity and Selectivity

The selective CO methanation (CO-SMET) process via Ru-Al2O3 catalysts was investigated as a tool for complete CO removal in fuel processors, when the H-2-rich gas so produced is employed for PEM-FCs applications to vehicles, boats, yachts and residential co-generators. CO-SMET seems, in fact, to be a good alternative to the most widely used CO preferential oxidation (CO-PROX) process. The performance of Ru-based catalysts on alumina carrier for efficient CO removal through CO-SMET was studied, exploring the role of two different Ru precursors (chloride and nitrate), and the doping effect of chloride and of Ru load (1%, 3% and 5%). First, two catalytic families (Ru-Al2O3_Cl and Ru-Al2O3_NO3) were prepared by incipient wetness impregnation of alumina powder synthesized via solution combustion synthesis, by varying the Ru load. Then, based on the best obtained results, a third catalytic family was prepared adding chloride to Ru-Al2O3_NO3 catalysts by impregnation. The CO removal performance was determined at catalyst powder level in a fixed bed micro reactor. Better performances were exhibited when Ru was deposited from chloride precursor, but the post-addition of chlorine to fresh Ru-Al2O3 catalysts prepared with nitrate precursor tremendously improved their selectivity toward CO methanation. In particular, with both 1% and 3% Ru-Al_NO3 catalyst chlorine doped, complete CO conversion was reached in a proper temperature range where the CO2 methanation was suitably kept at a low acceptable level.