Modulated Excitation Raman Spectroscopy of V₂O₅/TiO₂: Mechanistic Insights into the Selective Catalytic Reduction of NO with NH₃

We report the increased level of mechanistic information that Raman spectroscopy can provide when combined with modulated excitation experimentation. A V 2 O 5 /TiO 2 catalyst for the selective catalytic reduction (SCR) of NO x was subjected to periodic NH 3 pulses while recording time-resolved Raman spectra simultaneously. Through phase sensitive detection, we confirmed unambiguously that both VO x and TiO 2 play a dynamic role in the SCR process. Only a well-defined portion of VO x species (i.e., those that are coordinatively unsaturated) act as catalytic active centers while the majority remain largely unresponsive to the NH 3 pulses. Although TiO 2 is not directly involved in the SCR reaction, the phase-resolved Raman spectra demonstrate that it acts as a reservoir of NH 3 molecules that can be mobilized to the active sites. The inherent depth of these molecular insights goes beyond what is currently achievable with Raman experiments under steady-state conditions. Modulated excitation Raman spectroscopy can therefore advance the fundamental understanding of SCR and other metal oxide-catalyzed reactions.