NO Selective Catalytic Reduction over Atom-Pair Active Sites Accelerated via In Situ NO Oxidation

Selective catalytic reduction (SCR) of NO with NH₃ is the most efficient technology for NO emissions control, but the activity of catalysts decreases exponentially with the decrease in reaction temperature, hindering the application of the technology in low-temperature SCR to treat industrial stack gases. Here, we present an industrially practicable technology to significantly enhance the SCR activity at low temperatures (<250 °C). By introducing an appropriate amount of O₃ into the simulated stack gas, we find that O₃ can stoichiometrically oxidize NO to generate NO₂, which enables NO reduction to follow the fast SCR mechanism so as to accelerate SCR at low temperatures, and, in particular, an increase in SCR rate by more than four times is observed over atom-pair V₁-W₁ active sites supported on TiO₂(001) at 200 °C. Using operando SCR tests and in situ diffuse reflectance infrared Fourier transform spectra, we reveal that the introduction of O₃ allows SCR to proceed along a NH₄NO₃-mediated Langmuir-Hinshelwood model, in which the adsorbed nitrate species speed up the re-oxidation of the catalytic sites that is the rate-limiting step of SCR, thus leading to the enhancement of activity at low temperatures. This technology could be applicable in the real stack gas conditions because O₃ exclusively oxidizes NO even in the co-presence of SO₂ and H₂O, which provides a general strategy to improve low-temperature SCR efficacy from another perspective beyond designing catalysts.