Effect of potassium promoter on reaction performance of Rh/Al2O3 catalyst for CO selective oxidation in H-2-rich streams

It is indispensable to remove CO to less than 50 X 10(-6) from a H-2-rich feed gas for proton exchange membrane fuel cells. The promoting effect of potassium on the Rh/Al2O3 catalyst has been found in the CO preferential oxidation with O-2 under H-2-rich streams, CO conversion as high as 99.82% can be achieved, and methanation can be restrained. In this paper, the effect of potassium promoter on CO adsorption states and surface chemisorbed species in the CO selective oxidation process under H-2-rich streams over Rh/Al2O3 was investigated by in situ temperature-programming and FT-IR, CO-TPD and XRD. The results indicate that CO adsorption states on Rh/Al2O3 are not changed, but the CO adsorption intensity is weakened when potassium is added. The linear and bridged CO adsorbed on active sites of Rh-K/Al2O3 is fully desorbed at 120 and 180 degrees C, respectively. The mechanism of formate and carbonate species formation is also discussed. The experimental results of catalytic activity show that there exists an optimum loading of potassium on the Rh/Al2O3 catalyst to obtain both higher CO conversion and less methane product.