Highly Dispersed Ni with Partial Coverage of CeO _<i>x</i> Derived from NiCeO ₂ Solid Solution for the Selective Reverse Water Gas Shift Reaction

The reverse water gas shift (RWGS) reaction is a key process for CO2 utilization, and Ni-based catalysts are promising due to their high activity but often suffer from poor CO selectivity. Herein, NiCeO2 solid solution catalysts prepared via a coprecipitation method with varying Ni loadings and calcination and reduction temperatures were explored for the RWGS reaction at atmospheric pressure with varying reaction temperature, H2/CO ratio, and gas hourly space velocity (GHSV). Introducing a small amount of Ni (0.5 wt·%) to CeO2 enhanced the intrinsic activity dramatically by 95-fold, i.e., from 10.1 mmolCO·gcat–1·h–1 for CeO2–500C-600R to 960.8 mmolCO·gcat–1·h–1 for 0.5Ni–CeO2–500C-600R (calcined and reduced at 500 and 600 °C, respectively) at 600 °C and a H2/CO2 of 2, and lowered the Ea remarkably from 118.1 to 47.0 kJ·mol–1. The optimal sample of 0.5Ni–CeO2–500C-600R achieved near-equilibrium CO2 conversion with nearly 100% CO selectivity at 500–600 °C, a H2/CO of 2, and a GHSV of <100 L·gcat–1·h–1. Characterizations revealed that calcination at 500 °C enabled the formation of a NiCeO2 solid solution, and subsequent reduction at 600 °C generated highly dispersed Ni clusters partially covered by CeOx, which provide sufficient hydrogenation functionality with greatly weakened CO adsorption ability, giving rise to enhanced RWGS activity but suppressed methanation. This work provides insights into the structure evolution of NiCeO2 solid solution, which can be useful for designing solid-solution-derived catalysts for an efficient and selective RWGS reaction.