Experimental Microkinetic Approach of De-NOx by NH3 on V2O5/WO3/TiO2 Catalysts. 6. NH3–H2O Coadsorption on TiO2-Based Solids and Competitive Temkin Model

Abstract

The present study is a part of an experimental microkinetic approach (EMA) of the selective reduction of NOx to N2 with NH3 in excess O2 on V2O5/WO3/TiO2 catalysts (NH3-SCR process). In the temperature range of interest for NH3-SCR (T ≥≈ 473 K) and for three TiO2-based solids (sulfated and sulfate-free TiO2 supports and a sulfated 0.7% V2O5/9% WO3/TiO2 catalyst), FTIR spectroscopy and volumetric measurements with a mass spectrometer are used to study the impacts of the NH3–H2O coadsorption on the coverages of (a) the molecularly adsorbed NH3 species and (b) the molecularly and dissociated H2O species on Lewis and Bronsted sites. Whatever the solid, it is shown that NH3 dominates the molecular coadsorption on the Lewis sites. However, this does not prevent the dissociative H2O chemisorption on a small amount of Lewis acidic sites, leading to an increase in the amount of OH groups. On the two sulfated solids, these OH groups increase the amount of adsorbed NH4+ species as compared to the NH3 adsorption equi...