Selective catalytic reduction (SCR) of nitrogen oxides (NOx) by ammonia is the state-of-the-art NOx emission control technology for stationary sources, including power plants and industrial boilers. Supported VOx-WOx/TiO2 catalysts, which show high SCR activity, thermal stability and resistance to sulfur oxide poisoning, have long been practiced for commercial use. The mechanism of the SCR reaction on VOx-WOx/TiO2 catalysts, however, has been extensively studied and discussed without reaching a consensus with several key fundamental aspects still being debated are the (1) nature of the catalytic active sites, (2) most abundant reactive intermediates, (3) reaction mechanism and (4) rate-determining-step. To further understand the SCR reaction mechanism, a series of isotope switch experiments were performed using 15N18O, 18O2 and ND3. The involvement of isotopic labelled molecules was studied with temperature programmed surface reaction (TPSR). The participation of surface VOx sites during the isotope switch was monitored with in situ Raman. Operando IR-MS was performed during the NH3→ND3→NH3 isotope switch experiments to understand the participation of surface intermediates. Finally, the reduction-oxidation behavior of surface VOx species was studied by in situ UV-vis. Based on the multiple in situ and operando spectroscopy measurements, new fundamental insights were obtained about the SCR reaction mechanism and kinetics that will be presented.

Reaction mechanism for SCR of NO with NH3 by supported V2O5-WO3/TiO2 catalysts

253rd National Meeting (2017)

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