Effects of hydrocarbons on the performance of Cu/Na-MFI catalyst for NOX removal

Abstract

The selective catalytic reduction of NO with hydrocarbons in the presence of excess oxygen was investigated on metal ion-exchange zeolite and metallosilicate catalysts over a wide range of reaction temperature. Experimental results revealed that butane was the most active reductant followed by propene, ethane, and methane, respectively. Comparisons between saturated and unsaturated hydrocarbons showed that ethylene was a more active reductant than ethane whereas propylene showed low effectiveness compared with propane. The low activity of propylene was owing to the deactivation of the catalyst by carbonaceous deposits on the surface that caused the increment of pore size distribution. The catalytic activity of zeolite catalysts was also affected by the silicon to aluminum ratio and the amount of copper content. Furthermore, an increase in copper content of Cu-exchanged and Cu-incorporated H-form aluminosilicate catalysts expanded the range of temperature window of maximum NO conversion. The catalyst with copper ion-exchange and incorporate, Cu/Na-Cu◦Al-silicate, also showed both high catalytic activity and temperature window. The difference of various catalysts were investigated by temperature programmed desorption of carbon dioxide (CO(subscript 2) TPD). It was observed that only copper-exchanged zeolite with highly copper content showed the desorption peak of CO(subscript 2). This results suggests that copper ion site can adsorb CO(subscript 2). In addition, the relationship between cumulative CO(subscript 2) desorption and the content of copper ion-exchange (wt. %) can be considered as non-linear correlation.