Selective catalytic reduction of NOx over H-ZSM-5 under lean conditions using transient NH3 supply

The selective catalytic reduction (SCR) of NOx over zeolite H-ZSM-5 with ammonia was investigated using in situ FTIR spectroscopy and flow reactor measurements. The adsorption of ammonia and the reaction between NOx, O2 and either preadsorbed ammonia or transiently supplied ammonia were investigated for either NO or equimolar amounts of NO and NO2. With transient ammonia supply the total NO reduction increased and the selectivity to N2O formation decreased compared to continuous supply. The FTIR experiments revealed that NOx reacts with ammonia adsorbed on Brønsted acid sites as \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\rm NH}_{4}^{+}$$\end{document} ions. These experiments further indicated that adsorbed -\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\rm NO}_{2}^{-}$$\end{document} is formed during the SCR reaction over H-ZSM-5.