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.