A study of the mechanism of low-temperature SCR of NO with NH3 on MnOx/CeO2

• MnOx/CeO2 (DP) is a superior low-temperature NH3-SCR catalyst.
• The catalytic stability is totally different at 80 °C and 120 °C.
• A [NH3⋯NO−] complex is proved to be the intermediates.
• Decomposition of the intermediates is the rate-limiting step.

A MnOx/CeO2 supported catalyst was prepared using the deposition–precipitation (DP) method for low-temperature selective catalytic reduction (SCR) of NO with NH3. At short reaction time, nearly 100% NO conversion was obtained across the whole evaluated temperature range of 80–150 °C at a space velocity of 50,000 h−1. The catalyst rapidly lost its activity at 80 °C, while stable activity was achieved at 120 °C at a space velocity of 120,000 h−1 in a 36 h test. A possible reaction pathway is proposed based on the results of an in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study coupled with mass spectrometric (MS) data. It is suggested that the NH3-SCR reaction on the MnOx/CeO2 catalyst involves a [NH3⋯NO−] complex as an intermediate, the decomposition of which into N2 and H2O is the rate-limiting step. The role of oxygen in the SCR reaction is to reoxidize the reduced catalyst surface, thereby completing the catalytic cycle.

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