Sb-Containing Metal Oxide Catalysts for the Selective Catalytic Reduction of NOx with NH3

Qian Xu,Minh Ngoc Ha,Dandan Liu,Chuchu Wang,Qingping Ke,Wangcheng Zhan,Li Wang,Yanglong Guo,Yun Guo

doi:10.3390/catal10101154

Abstract

Sb-containing catalysts (SbZrOx (SbZr), SbCeOx (SbCe), SbCeZrOx (SbCeZr)) were prepared by citric acid method and investigated for the selective catalytic reduction (SCR) of NOx with NH3 (NH3-SCR). SbCeZr outperformed SbZr and SbCe and exhibited the highest activity with 80% NO conversion in the temperature window of 202–422 °C. Meanwhile, it also had good thermal stability and resistance against H2O and SO2. Various characterization methods, such as XRD, XPS, H2-TPR, NH3-TPD, and in situ diffuse reflectance infrared Fourier transform (DRIFT), were applied to understand their different behavior in NOx removal. The presence of Sb in the metal oxides led to the difference in acid distribution and redox property, which closely related with the NH3 adsorption and NO oxidation. Brønsted acid and Lewis acid were evenly distributed on SbCe, while Brønsted acid dominated on SbCeZr. Compared with Brønsted acid, Lewis acid was slightly active in NH3-SCR. The competition between NH3 adsorption and NO oxidation was dependent on SbOx and metal oxides, which were found on SbCe while not on SbCeZr.

Highlights

Nitrogen oxide (NOx ), one of the main environmental contaminants emitted from stationary sources and mobile sources, causes photochemical smog, acid rain, and the depletion of the ozone layer [1,2]
SbCeZr exhibited the higher performance in NH3 -selective catalytic reduction (SCR) than SbCe and SbZr, and NOx could be removed with 80% conversion in the temperature range of 202–422 ◦ C
SbCeZr seemed to be a good candidate for the practical application in deNOx

Summary

Introduction

Nitrogen oxide (NOx ), one of the main environmental contaminants emitted from stationary sources and mobile sources, causes photochemical smog, acid rain, and the depletion of the ozone layer [1,2]. Several technologies have been proposed for NOx removal, such as direct decomposition of NOx , NOx storage reduction (NSR), and the selective catalytic reduction (SCR) process with ammonia (NH3 -SCR) or hydrocarbons (HC-SCR). The NH3 -SCR process has been proven to be the efficient method to satisfy the restrict regulations of NOx emissions [3]. The enhanced oxidation activity at low temperature promotes NOx selective reduction, while it takes a risk for the depletion of NH3 at high temperature leading to the decrease in NO reduction. The reaction thermal shock and exhaust components (H2 O and SO2 ) put forward strict requirements on the design of NH3 -SCR catalysts

Methods

Results

Discussion

Conclusion