Sulfate residuals on Ru catalysts switch CO₂ reduction from methanation to reverse water-gas shift reaction

Efficient heterogeneous catalyst design primarily focuses on engineering the active sites or supports, often neglecting the impact of trace impurities on catalytic performance. Herein, we demonstrate that even trace amounts of sulfate (SO₄^2-) residuals on Ru/TiO₂ can totally change the CO₂ reduction from methanation to reverse-water gas shift (RWGS) reaction under atmospheric pressure. We reveal that air annealing causes the trace amount of SO₄^2- to migrate from TiO₂ to Ru/TiO₂ interface, leading to the significant changes in product selectivity from CH₄ to CO. Detailed characterizations and DFT calculations show that the sulfate at Ru/TiO₂ interface notably enhances the H transfer from Ru particles to the TiO₂ support, weakening the CO intermediate activation on Ru particles and inhibiting the further hydrogenation of CO to CH₄. This discovery highlights the vital role of trace impurities in CO₂ hydrogenation reaction, and also provides broad implications for the design and development of more efficient and selective heterogeneous catalysts.