Effect of ZrO2 addition on de-NOx performance of Cu-ZSM-5 for SCR catalyst

Abstract

The aim of the present study is to investigate the de-NOx performance of a Cu-ZSM-5 catalyst to which ZrO2 additives are added to improve the low-temperature activity and durability of the selective catalytic reduction (SCR) catalyst for diesel vehicles. The main experimental parameters are the amount of ZrO2 added, hydrothermal aging temperature, type of hydrocarbon (HC) and concentration of sulfur (S). The results showed that the NOx conversion of the Cu-ZSM-5-ZrO2 (2wt%) catalyst was improved by 10–20% compared to that of the Cu-ZSM-5 or Fe-zeolite catalyst in the temperature range of 200–300°C, because the addition of an appropriate amount of ZrO2 additive can improve the activation of the Cu-ZSM-5-ZrO2 (2wt%) catalyst by enhancing the acidity of the SCR catalyst. The Cu-ZSM-5-ZrO2 (2wt%) catalyst was the (most?) resistant against hydrothermal aging, (because the?) ZrO2 additives can advance the activation of the Cu-ZSM-5 catalyst by promoting its thermal stability. Alkenes such as propylene (C3H6) containing a double bond in the reaction gases had a more negative effect on the de-NOx performance of the Cu-ZSM-5 catalysts than other hydrocarbons. The curve of the de-NOx performance of the Cu-ZSM-5 catalysts in the presence of C3H6 decreased rapidly in the range of 200–350°C and then increased again to form an M-shaped curve due to the blocking of the SCR reaction. Although the recovery rate of the de-NOx performance for Cu-ZSM-5-ZrO2 (2wt%) from sulfur poisoning was not reversible, it was higher than those of the Cu-ZSM-5-ZrO2 (0 and 4wt%) catalysts, because it contained the proper amount of ZrO2. The proper amount of ZrO2 for the Cu-ZSM-5 SCR catalyst was 2wt%.