Study On Water Gas Shift Catalysts For Onboard Hydrogen Production

In this paper, Pt/CeO2-ZrO2 water gas shift catalysts were developed for the onboard fuel processing in PEM fuel cell vehicles.The pellet catalysts were prepared by co-precipitation and impregnation. The best catalysts composition was achieved by screening the catalysts with different support and active metal loading. The monolithic catalysts were prepared by coating technology and the composition was also optimized.These catalysts were tested under different operation conditions. It is shown that the best catalyst is active in a wide temperature window above 250 ℃. The conversion was increased greatly by increasing the ratio of steam to gas. The catalysts can be operated while CO concentration varies from 4 vol% to 10 vol%.The catalysts are stable at high temperature in oxidation/reduction cycling that may occur in an automotive fuel processor. Both the pellet and monolithic catalysts are stable when exposed to air at 300℃ and the high activity remains in several start-up and shutdown cycles. The stability of the monolithic catalyst was tested for 160h, without deactivation.The formation of CeO2-rich solid solution in the CeO2-ZrO2 composite oxides gives better performance, as shown by XRD carried out on the aged catalysts, and this is similar to the case in automotive three-way catalysts. The correlation between the metal dispersion determined by H2-adsorption and the activity of catalyst wasinvestigated. It is shown that the higher metal dispersion results in the better activity. The intrinsic kinetics of water gas shift reaction over the catalyst was investigated and a power-type rate model was established:The water gas shift reaction over this catalyst agrees well with the redox mechanism.