Influence of Feed Gas Composition HOCO Ratio and Presence of Hydrogen

In Figure 8.13 we observe the importance of utilizing the right feed-gas composition over the Cu02Ce0.8O2-y catalyst prepared by coprecipitation method. The dotted lines represent different equilibrium curves calculated for three different feed mixtures: 0.5% CO and 1.5% H2O; 1.8% CO and 1.8% H2O; and 50% H2, 0.5% CO, 1.5% H2O, all diluted with He. The first mixture (0.5% CO and 1.5% H2O) represents a suitable feed-gas composition for the WGS reaction, where high conversions (>99% CO conversion up to 550 K) can be accomplished. It is in this equilibrium conversion region that the WGS reaction has to be carried out.

The experiments with 1/1 CO/H2O feed were carried out to show how fast the WGS equilibrium is approached due to the lower water content in the feed-gas composition. It can be seen that the lower (stoichiometric) CO/H2O ratio in the feed does not influence the rate of approach to the equilibrium. This confirms the observations of Qi et al. [42] that water has little or no effect on the reaction rate in the case of ceria-supported transition metal catalysts.

Temperature (K)

FIGURE 8.13 The influence of increasing the ratio between water and carbon monoxide, and addition of 50% H2 to the feed-gas mixture. CO conversion in WGS reaction over Cu0.2Ce0.8O2-y, catalyst at different feed compositions with a S.V. = 5000 h-1. The solid lines are model fits assuming first-order reversible kinetics. The dotted lines represent the equilibrium conversions for the specific feed compositions.

Temperature (K)

FIGURE 8.13 The influence of increasing the ratio between water and carbon monoxide, and addition of 50% H2 to the feed-gas mixture. CO conversion in WGS reaction over Cu0.2Ce0.8O2-y, catalyst at different feed compositions with a S.V. = 5000 h-1. The solid lines are model fits assuming first-order reversible kinetics. The dotted lines represent the equilibrium conversions for the specific feed compositions.

The feed mixture containing a large amount of hydrogen (50% H2, 0.5% CO, and 1.5% H2O) was also used. This feed composition represents conditions that are close to those used in the industry with regard to H2 content: 473 K, 30 bar, and a steam-to-dry-gas ratio of 0.4 with a dry gas composition of 2% CO, 20% CO2, and 78% H2 [24]. The intent was to examine the behavior of the catalysts in the presence of H2 in the gas feed, which could cause methanation reactions. Yet the typical industrial gas composition has an equilibrium conversion even higher than the gas mixture with 0.5% CO and 1.5% H2O, since the high amount of H2O shifts the WGSR equilibrium to the right side of Equation 8.10.

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