NH3-Selective Catalytic Reduction of NOx to N2 over Ceria Supported WOx Based Catalysts: Influence of Tungsten Content

Imane El Arrouji,Jamil Toyir,Kai C Szeto,Mostafa Taoufik,Cuirong Chen,Cherif Larabi,Abdallah Oulmekki,Aimery De Mallmann

doi:10.3390/catal11080950

Abstract

A series of HPW/CeO2 catalysts generated from 12-tungstophosphoric acid, H3PW12O40 (HPW), supported on ceria and presenting different tungsten loadings (2, 4.5, 9, 16, and 40 wt% W) were prepared and characterized by N2 physisorption, XRD, IR, Raman, and UV-Vis. The different characterization techniques suggested that low loading of tungsten resulted in mainly isolated sites, while high tungsten loading produced polymeric or tungsten clusters. Those materials exhibited high activity in NH3-SCR of NOx into N2. Moreover, the series of experiments indicated that low loading in tungsten (2% HPW/CeO2) displayed the highest activity with a remarkable N2 selectivity (99%) at medium-high temperature (300–515 °C), owing to the high amount of monomeric tungstate coverage on the catalyst surface.

Highlights

In the last decades, growing interest has been given to developing novel technologies for reducing the harmful gases in environment
In the high temperature region, an increase in the TOF values is observed with lower tungsten contents. These findings indicate that the polymeric tungsten species can readily perform selective catalytic reduction (SCR) of NO in the low temperature region, while the isolated tungsten species are more active in the high temperature region
Polymeric tungsten species can readily perform SCR of NO in the low temperature region, while the isolated tungsten species are more active in the high temperature region

Summary

Introduction

In the last decades, growing interest has been given to developing novel technologies for reducing the harmful gases in environment. NOx selective catalytic reduction (SCR) technology is classified according to the reducing agents used, such as hydrocarbons [7], oxygenated hydrocarbons [8,9], hydrogen [10], or ammonia (or urea) [11,12]. The latter is regarded as an efficient approach to reduce NOx emissions due to its high selectivity and relatively simple implementation (without compromising the engine efficiency). For the NH3-SCR, HPW has been used as precursor on ceria (CeO2) to improve the NH3 adsorption ability after calcination [25] This catalyst shows a poor performance that may be due to low surface area, low dispersion of the tungsten species, and uncontrolled synthesis method. Special attention is addressed to the structure analysis of the materials using X-ray diffraction, FTIR, and Raman spectroscopy, to the surface characterization by means of N2 adsorption, in relationship with NH3-SCR performance

Characterization of the Catalysts

Catalytic Activity

Catalysts Measurement

Conclusions