The continued interest for low temperature applications for vanadium titania based NH3-SCR catalysts motivates continued fundamental research. The development of operando spectroscopic techniques in combination with theoretical descriptions provide insightful visions. Mechanistic discussions regarding the SCR reaction pathway and the structure of the surface intermediates have been focussed on the discussion of the importance of the Lewis and Brønsted acid sites for ammonia and nitrogen oxide activation. The Lewis acid sites have been assumed to be V or V-O-M (M = Ti or V) sites that directly correlates to the extent of IR signal from the NH3 bending mode at 1620 cm-1 while the V-OH groups have been regarded as Brønsted acid sites with a signal correlating with the NH4+ signal at 1450 cm-1. In this work, we discuss these assumptions in the context of the presence of multiple oxidation states of vanadium on the two most common facets of the carrier a-TiO2 material. By operando SSITKA-FTIR-MS-, in situ Raman and UV-vis spectroscopy studies and DFT modelling we discuss how the NH3 signals relates to the surface sites on the catalyst. We furthermore discuss the structure of the reduced sites and suggest reoxidation pathways. Finally, we will show why the V-OH group remains of significant importance for the SCR reaction.

Operando investigation on the structure and reactivity of adsorbed NH3, NOX & V=O species during SCR on shaped vanadia catalyst

255th National Meeting (2018)

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