K and Na Promotion Enables High-Pressure Low-Temperature Reverse Water Gas Shift over Copper-Based Catalysts

Abstract

The conversion of CO2 and clean H2 to CO and H2O via the reverse water-gas shift reaction (rWGS) yields sustainable synthesis gas and opens up routes to low-carbon fuels via subsequent conventional processes such as Fischer-Tropsch synthesis which typically takes place between 200 and 350 °C. However, other CO2 hydrogenation products, such as methane and methanol, are thermodynamically much more stable at temperatures below 600-700 °C and at higher pressures. It is hence highly desirable to develop CO-selective rWGS catalysts that are active at low temperatures to facilitate process integration. We studied alkali-promoted Cu-based catalysts at varying pressure (20-40 bar(g)), temperature (180-260 °C), and H2:CO2 feed ratio (1:1, 3:1, 9:1). The addition of either K or Na boosted the CO2 conversion about 3-fold for carbon-supported Cu catalysts reaching equilibrium conversion at 260 °C, an effect that was not observed for silica-supported catalysts. Even at high pressures and high H2 content in the feed, the selectivity to CO remained close to 100%, showing that the K and Na promoters completely suppressed methanol and methane formation in these systems. The remarkable overall performance of these catalysts opens perspectives on the low-temperature operation of the rWGS reaction to produce sustainable fuels and building blocks.