Global Kinetic Modeling of Reactions Occurring during Selective Catalytic Reduction of NO by NH₃ over Vanadia/Titania-Based Catalysts

Abstract

The global kinetics of the reactions occurring during the selective catalytic reduction (SCR) of NO by NH3 over vanadia-based commercial DeNOx catalysts has been studied. The global kinetic model developed accounts for three chemical reaction pathways (Eley−Rideal and Langmuir−Hinshelwood type SCR and ammonia oxidation) occurring in this system and considers the effects of intraparticle diffusion phenomena. The model is applied to describe the global kinetics in the broad temperature range from 140 to 475 °C. New insight in the interplay between the processes occurring during SCR has been gained by considering the influence of the concentration of oxygen and water, the weak adsorption of NO at low temperatures (T ≤ ca. 200 °C), the decrease of the NH3 coverage at high temperatures (T ≤ ca. 350 °C), the relevance of the Langmuir−Hinshelwood type SCR at temperatures below ca. 200 °C, the occurrence of NH3 oxidation as a side reaction at temperatures above ca. 300 °C, and the role of intraparticle diffusion.