Assignment of Vibrational Bands of Critical Surface Species Containing Nitrogen in the Selective Catalytic Reduction of NO by NH₃

Abstract

The selective catalytic reduction (SCR) of NO by NH 3 on metal oxides plays a key role in minimizing NO x emissions. Electronic structure calculations at the density functional theory level have been performed to predict the vibrational modes of NH 3 /NH 4 + bound to validated cluster models of vanadium oxide bound to a TiO 2 surface. Excellent agreement of the scaled calculated values with the observed bands attributed to surface-bound species is found. The presence of NH 3 bound to Lewis acid sites and NH 4 + bound to Brønsted acid sites when VOH groups are present is supported by our predictions. NH 4 + is expected to dominate the spectra even at low concentrations, with predicted intensities 5 to 30 times greater than those predicted for surface-bound NH 3 . This is particularly evident in the lowestenergy N-H stretches of surface NH 4 + due to partial proton transfer interactions with the vanadium oxide surface model. The current work is consistent with experimental vibrational spectroscopy results and does not support the presence of a significant amount of NH 2 on the catalyst surface for the SCR reaction on VO x /TiO 2 . The combined experimental and computational results support the presence of both NH 3 -and NH 4 + -type species bound to the surface.

Prediction of the structures and heats of formation of MO2, MO3, and M2O5 for M = V, Nb, Ta, Pa

“…The calculated bond dissociation energies (BDEs) for the single bond M-O and double bond MQO are reported in Table 9 with experimental comparisons provided where available. The BDEs for the MQO, where calculated as half the total atomization energy of the metal dioxide, MO 2 molecule with two double bonded O, eqn (9).…”

“…1,2 As an example, vanadium oxide catalysts are used for a number of important reactions, including the oxidation of methanol, 3 industrial sulfuric acid production, and the removal of NO x pollutants from combustion processes via selective catalytic reduction (SCR) reactions. [4][5][6] Small vanadium oxide clusters have been used to model a range of catalytic activities [7][8][9] using structures based on a combined NMR and computational determination of the structures of the supported clusters. 10,11 Oxides of niobium and tantalum have received attention in high temperature chemistry and for optical applications.…”