Sulfur-tolerant lanthanide oxysulfide catalysts for the high-temperature water–gas shift reaction

We report on the high activity and stability of lanthanide oxysulfides, e.g., of La2O2S or Pr2O2S, as catalysts for the high temperature water–gas shift (WGS) and the reverse water gas shift (RWGS) reactions. The catalytic activity derives from a very large oxygen storage capacity based on the redox of the sulfur ion in the interconverting oxysulfide/oxysulfate phases during reaction. The WGS reaction lights off at around 400 °C and reaches equilibrium at temperatures >750 °C in tests conducted at high space velocities (∼14,000 h−1). No loss of sulfur or catalyst deactivation is observed with time-on-stream in sulfur-free gas mixtures at all temperatures. These catalysts have fivefold lower aerial reaction rates (μmol/m2/s) than commercial Fe–Cr catalysts at 400 °C. However, unlike the iron oxide-based catalysts, they can be used up to 800 °C with high levels of H2S (700 ppm) present in the gas mixture. Inhibition by sulfur at lower temperatures was fully reversible.

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► Lanthanide oxysulfides active catalysts for high temperature WGS and RWGS reactions.
► Reaction lights off ∼400 °C and above 750 °C equilibrium conversions are reached.
► No loss of sulfur with time-on-stream over the temperature range from 400 to 800 °C.
► Superior performance than commercial Fe–Cr in gas feed containing 700 ppm H2S.
► Complete sulfur tolerance at 800 °C and partial inhibition at 600 °C with 700 ppm H2S.