(520e) Rare Earth Oxysulfides as High-Temperature Catalysts for the Water-Gas Shift Reaction

Lanthanide oxides, have been extensively studied not only as sorbent materials for high temperature removal of H2S, but also as the primary support for Pt, Pd, Cu, Ni, and Au for low- and high-temperature redox reactions, such as the WGS reaction. The excellent adsorption capacity of presulfided samples, the evidence from previous tests of RWGS catalysis and their enhanced oxygen storage capacity recently reported present a new potential of these materials as sulfur-resistant catalysts for the high temperature water-gas shift reaction. We report here on the activity and stability of lanthanide oxysulfides and oxysulfates as catalysts for the high temperature water?gas shift reaction (WGS). The key element for the catalytic activity of these materials is their enhanced oxygen storage capacity and thus reducibility based on the sulfur anion. This oxygen shuttling mechanism involves the entire bulk of these materials and occurs at temperatures higher than 600oC which makes them perfect candidates for the high temperature water gas shift reaction. The reaction lights off at around 450oC and at high temperatures CO2 conversions close to equilibrium are achieved. The apparent activation energy and reaction rates are measured and compared to those of Fe2O3 and lanthanum-doped ceria. Nevertheless, the most important feature of these materials is their tolerance to sulfur compounds as confirmed by spiking the feed gas with different ppm amounts of H2S. Formulation of such kind of WGS catalyst, able to maintain activity both in the presence and absence of sulfur in the feed gas, would constitute a major breakthrough and a key step in the effort to combine and integrate processing units of the fuel cell system in power generation.