Transforming a CO2 Adsorbent to a RWGS Catalyst by Controlling MgO Defects with Ce Single Atoms

The reverse water gas shift reaction (RWGS) is an important industrial reaction in the value chain to convert CO2 to enable carbon circularity. MgO is a typical absorbent of CO2 that forms stable surface carbonates. We demonstrate that highly defective MgO nanocrystals (c.a. 20 nanometers) are instead an active catalyst for RWGS. Their performances can be significantly enhanced by adding atomically dispersed Ce atoms anchored at these defective MgO sites. Extensive mechanistic studies and theoretical modelling prove that CO2 catalytic conversion depends on the MgO defective sites. Ce mainly promotes their number. Even if their presence influences the rate-limiting step, the activation energy remains unchanged, with the activity increase related to the pre-exponential factor. The Ce-doped MgO nanocrystal reached the RWGS equilibrium conversion at 600°C with CO product selectivity > 99%, maintained for over 850 hours on stream. The comparison with state-of-the-art evidence of their superior performances.