OPTIMIZATION OF THE SELECTIVE CATALYTIC REDUCTION OF NO IN DIESEL EXHAUST OVER CU-ZN/ZSM-5 CATALYST USING CENTRAL COMPOSITE DESIGN

Abstract

The optimization of the operating conditions in nitric oxide (NO) selective catalytic reduction (SCR) process over Cu-Zn/ZSM-5 bimetallic catalyst using combined Response Surface Methodology (RSM) and Central Composite Design (CCD) is reported. A bimetallic catalyst containing 6 wt. % Cu and 8 wt. % Zn was prepared through a combined impregnation and ion-exchange process. The process conditions investigated were temperature (300 -400 ?C), NO concentration (900-2,000 ppm) and iso-butane (reductant) concentration (900 - 2,000 ppm). The weight hourly space velocity (WHSV) was fixed at 13,000 h-1. Cu-Zn/ZSM-5 catalyst proved its potential for the SCR process. Statistical analyses showed that the NO reduction was affected by all the operating conditions with the temperature as the most dominant one. Based on the experimental design, a second order mathematical model was successfully developed and satisfactory fitting to the experimental data was demonstrated. Interactions between variables were also analyzed at 99.99 % confidence level. The optimum conditions obtained were 624 ppm for the NO concentration, 2,440 ppm for the iso-butane concentration and 389 °C for the reaction temperature to give a corresponding NO reduction of  96.13 %.