A study on biometallic water gas shift catalysts to be used ın fuel processing

Abstract

The aim of this study is to design and develop a Au-based, bimetallic WGS catalyst which has suitable activity and selectivity characteristics to be used in a fuel processor. The catalyst composition, preparation method, calcination temperature, reduction temperature and reduction mixture composition, and feed composition were the parameters used in the catalyst design and testing studies. Nine different catalyst samples were prepared, tested and they are characterized by SEM. The optimum catalyst composition for WGS reaction was found to be 1% Re-2% Au/ZrO2, prepared by impregnation of Re on ZrO2 followed by deposition precipitation of Au (Re+Au). Addition of Re in this sequence was observed to improve the catalytic activity significantly, suggesting that rhenium is a good promoter for bimetallic gold based WGS catalysts. Together with five other different realistic feed compositions, a reaction mixture of 6% CO, 36% H2O, 39% H2, 10% CO2, 9% He was used for most of the reaction tests performed. The WGS activities of the samples were determined for 250-350 ˚C range. Effect of W/F ratio (0.02, 0.03, 0.06) and H2O/CO ratio (5, 6 and 7) on the WGS performance of Re-Au bimetallic catalysts were also investigated, and as expected, the general trend observed was that the catalytic activity increases with increasing W/F and H2O/CO ratios, with the exception that the catalytic activity was found to be very close for all W/F ratios at 350 ˚C. For optimum catalyst composition and reaction conditions, the catalytic activity was observed to reach as high as 55% CO conversion at 350 ˚C. Trace amounts of methane formation was observed only for the samples prepared by Au+Re sequence at 350 ˚C. No methane activity was observed for the rest of the samples. The results of the current study indicate that the bimetallic Re-Au catalyst supported on zirconia has a real potential to be used in the WGS unit of a real fuel processor.