Study On Catalytic Behaviors Of Precious Metal Modified Molybdenum Carbide Catalysts For Low-temperatre Water Gas Shift Reaction

The water gas shift (WGS) reaction is an essential compontent of reformate fuel gas upgrading processes for hydrogen production. It’s of particular importance for polyer electrolyte membtane fuel cell applications, where CO could be react with H2O to produce H2. The WGS reaction is a wildly exothermic reaction. From a thermodyramic view point, the equilibrium conversion is lower at high WGS reaction temperature, and the low temperature is more conduction to the reaction. However, the reaction rate is slower at low temperature which was limited for the kinctics. Therefore, it’s important to investigate the activity for the low temperature WGS reaction.In this work, we compared the activity of the various nobal metals (Au, Pt, Pd) modified molybdenum carbide catalysts for the WGS reaction, and put focus on the activity and durability of molybdenum carbide supported Au catalyst. The modified catalysts have been characterized in terms of XRD, BET, XPS, SEM, HRTEM, and CO Chemisorption measurements. Associated the results of characterized and the porfrmance of the catalyst, the following results were achived:(1) The Au modified molybdenum carbide catalysts showed superior cativity for the low temperature WGS reaction,2.2%Au/MoCx achived95%CO conversion at150℃, in the10.5%CO,21%H2O,20%N2/Ar, GHSV=90,000mlg-1h-1. Indeed, the reaction rate in the CO conversion of Au is1.073molco/molAu*s, it appears to be higher than the most active catalyst reported in the literature.(2) The characterized results suggested that there were stronger interaction between Au and molybdenum carbide after the carbonization, which facilitated the dispersion of Au. The XPS results indicated that the metalic Au, as well as little Au1+was the main Au species on the Au/MoCx catalyst. The bulk structure of the Au/MoCx didn’t change after the reaction, and the decline of the activity was due to the intermediates deposited on the surface.(3) The study of the WGS reaction mechanism of Au/MoCx suggested that:for the a-MoC1-x and2.2%Au/MoCx catalysts, the reaction followed the formate association mechanism at low temperature and the regenerative redox mechanism at high temperature respectively. Whereas β-Mo2C catalyst follows the regenerative redox mechanism at entire temperature ranges. At low temperatures, the activity of CO conversion was variant for the three catalysts which lead to the different activity and reaction mechanism. (4) The effects of molybdenum carbide morphology and the reaction atmosphere on the catalytic properties were investigated for the low temperature WGS reaction. The pure phase a-MoC1-x supported Au catalyst should be the best activity for the WGS reaction, while the activity of pure phase P-Mo2C supported Au catalyst is very low. Which indicate that the origin of the super activity at low temperature was from the strong interaction between a-MoC1-x and Au. A strong enhanced effect of addition hydrogen was observed at the high temperature, while the activity was decline in the addition of H2at low temperature.