Selective Catalytic Reduction of Nitric Oxide with Propylene over Fe/Beta Catalysts Under Lean-Burn Conditions

Hao Zhou,Huishuang Zhao,Shiguo Wu,Yaxin Su,Mengyu Li,Mengyao Ge

doi:10.3390/catal9020205

Abstract

Fe/Beta catalysts were used for the selective catalytic reduction of nitric oxide with propylene (C3H6-SCR) under lean-burn conditions, which were prepared by liquid ion-exchange (LIE), solid-state ion-exchange (SIE), and incipient wet-impregnation (IWI) methods. The iron species on Fe/Beta were characterized and identified by a combination of several characterization techniques. The results showed preparation methods had a significant influence on the composition and distribution of iron species, LIE method inclined to produce more isolated Fe3+ ions at ion-exchanged sites than IWI and SIE method. C3H6-SCR activity tests demonstrated Fe/Beta(LIE) possessed remarkable catalytic activity and N2 selectivity at temperature 300–450 °C. Kinetic studies of C3H6-SCR reaction suggested that isolated Fe3+ species were more active for NO reduction, whereas Fe2O3 nanoparticles enhanced the hydrocarbon combustion in excess of oxygen. According to the results of in situ DRIFTS, more isolated Fe3+ sites on Fe/Beta(LIE) would promote the formation of the key intermediates, i.e., NO2 adspecies and formate species, then led to the superior C3H6-SCR activity. The slight decrease of SCR activity after hydrothermal aging of Fe/Beta(LIE) catalyst might be due to the migration of isolated Fe3+ ions into oligomeric clusters and/or Fe2O3 nanoparticles.

Highlights

Nitric oxides (NOx ) from combustion exhaust gas are the major air pollutants drive to the formation of photochemical smog and haze [1,2]
It could be assumed that the ferric ions at ion-exchange sites, which might be the main product with liquid ion-exchange (LIE) method, would little affect the textural properties of Beta zeolite
We studied the selective catalytic reduction of NO with C3 H6 over Fe/Beta catalysts prepared by LIE, state ion-exchange (SIE), and incipient wet-impregnation (IWI) methods

Summary

Introduction

Nitric oxides (NOx ) from combustion exhaust gas are the major air pollutants drive to the formation of photochemical smog and haze [1,2]. Selective catalytic reduction of NOx by hydrocarbons (HC-SCR) is a promising technology for reducing NOx , which can achieve the elimination of both hydrocarbons and nitric oxides in pollution source at the same time [3]. Transition metal (e.g., Cu, Fe) modified zeolites exhibit remarkable catalytic activity in the HC-SCR process, many studies have been conducted on zeolite structure, metals nature and preparation methods of zeolite catalysts [4,5,6]. Zeolites with Chabazite (CHA) structure, such as SSZ-13 [9,10] and SAPO-34 [11,12], have received much attention due to their outstanding hydrothermal durability and activity in the NH3 -SCR. Fe-based zeolites (e.g., Fe/ZSM-5 and Fe/Beta) are more attractive for HC-SCR because of their appropriate

Results

Discussion

Conclusion