Intermediate-Temperature Reverse Water–Gas Shift under Process-Relevant Conditions Catalyzed by Dispersed Alkali Carbonates

Current reverse water-gas shift (RWGS) technologies require extreme temperatures of >900 °C. The ability to perform RWGS at lower temperatures could open new opportunities for sustainable chemical and fuel production, but most catalyst materials produce methane and coke at lower temperatures, especially at elevated pressures targeted for industrial processes. Here we show that transition-metal-free catalysts composed of K₂CO₃ or Na₂CO₃ dispersed on commercial γ-Al₂O₃ supports (K₂CO₃/γ-Al₂O₃ and Na₂CO₃/γ-Al₂O₃) are highly effective RWGS catalysts in the intermediate-temperature regime. At a high gas hourly space velocity of 30,000 h^-1 and operating pressure of 10 bar, K₂CO₃/γ-Al₂O₃ reached RWGS equilibrium-limited CO₂ conversion at 550 °C and was 100% selective for CO at all temperatures tested (up to 700 °C). Na₂CO₃/γ-Al₂O₃ was also 100% CO-selective and only slightly less active. Both catalysts were stable for hundreds of hours on stream at 525 °C and tolerated large quantities of methane and propane impurity in the CO₂/H₂ feed. The unique performance attributes, combined with the low-cost components and extremely simple synthesis, make dispersed carbonate RWGS catalysts attractive options for industrial application.