Water-Gas Shift Kinetics Over Iron Oxide Catalysts at Membrane Reactor Conditions

Abstract

This report covers the second year of a project investigating water-gas shift catalysts for use in membrane reactors. It has been established that a simple iron high temperature shift catalyst becomes ineffective in a membrane reactor because the reaction rate is severely inhibited by the build-up of the product CO 2 . During the past year, an improved microkinetic model for water-gas shift over iron oxide was developed. Its principal advantage over prior models is that it displays the correct asymptotic behavior at all temperatures and pressures as the composition approaches equilibrium. This model has been used to explore whether it might be possible to improve the performance of iron high temperature shift catalysts under conditions of high CO 2 partial pressure. The model predicts that weakening the surface oxygen bond strength by less than 5% should lead to higher catalytic activity as well as resistance to rate inhibition at higher CO 2 partial pressures. Two promoted iron high temperature shift catalysts were studied. Ceria and copper were each studied as promoters since there were indications in the literature that they might weaken the surface oxygen bond strength. Ceria was found to be ineffective as a promoter, but preliminary results with copper promoted FeCr high temperature shift catalyst show it to be much more resistant to rate inhibition by high levels of CO 2 . Finally, the performance of sulfided CoMo/Al 2 O 3 catalysts under conditions of high CO 2 partial pressure was simulated using an available microkinetic model for water-gas shift over this catalyst. The model suggests that this catalyst might be quite effective in a medium temperature water-gas shift membrane reactor, provided that the membrane was resistant to the H 2 S that is required in the feed.4

Investigation of hydrogen production from model bio-syngas with high CO2 content by water-gas shift reaction

“…It is known that CO 2 is one of the products of WGSR, and high CO 2 level will limit the reaction equilibrium. Lund et al [14] tested WGSR with membrane reactor, reported that the activity of FeeCr catalyst was affected by CO 2 significantly, and suggested that CoeMo/Al 2 O 3 catalyst which was not inhibited by CO 2 may be the better candidate for WGSR in membrane reactor. CoeMo/Al 2 O 3 sulfide-resistant catalyst needs to be pre-sulfide and working under the stream containing sulfide [15], which is extremely low in bio-syngas.…”

Non-precious metal (pre-)commercial catalysts for Pd membrane water gas shift

“…Differences in the rate expressions among the authors have been especially marked in their opinion on the reaction mechanism and whether work was conducted under conditions with diffusion limitation. More information on the various mechanisms can be found by Lund et al [13]. (carbonate mechanism), Newsome [14], Tinkle and Dumesic [15] (the oxidation-reduction mechanism (regenerative mechanism).…”