Effect of Copper Precursors on the Activity and Hydrothermal Stability of CuII−SSZ−13 NH3−SCR Catalysts

Meixin Wang,Zhanggen Huang,Weiren Bao,Changming Zhang,Yaqin Hou,Jiancheng Wang,Liping Chang,Zhaoliang Peng,Mengmeng Liu,Lina Han

doi:10.3390/catal9090781

Abstract

A series of CuII−SSZ−13 catalysts are prepared by in-situ hydrothermal method using different copper precursors (CuII(NO3)2, CuIISO4, CuIICl2) for selective catalytic reduction of NO by NH3 in a simulated diesel vehicle exhaust. The catalysts were characterized by X−ray diffraction (XRD), scanning electron microscope (SEM), X−ray photoelectron spectroscopy (XPS), N2 adsorption-desorption, hydrogen-temperature-programmed reduction (H2−TPR), ammonia temperature-programmed desorption (NH3−TPD), and 27Al and 29Si solid state Nuclear Magnetic Resonance (NMR). The CuII−SSZ−13 catalyst prepared by CuII(NO3)2 shows excellent catalytic activity and hydrothermal stability. The NO conversion of CuII−SSZ−13 catalyst prepared by CuII(NO3)2 reaches 90% at 180 °C and can remain above 90% at a wide temperature range of 180–700 °C. After aging treatment at 800 °C for 20 h, the CuII−SSZ−13 catalyst prepared by CuII(NO3)2 still exhibits above 90% NO conversion under a temperature range of 240–600 °C. The distribution of Cu species and the Si/Al ratios in the framework of the synthesized CuII−SSZ−13 catalysts, which determine the catalytic activity and the hydrothermal stability of the catalysts, are dependent on the adsorption capacity of anions to the cation during the crystallization process due to the so called Hofmeister anion effects, the NO3− ion has the strongest adsorption capacity among the three kinds of anions (NO3−, Cl−, and SO42−), followed by Cl– and SO42– ions. Therefore, the CuII−SSZ−13 catalyst prepared by CuII(NO3)2 possess the best catalytic ability and hydrothermal stability.

Highlights

The emission of nitrogen oxides is a major cause of unhealthy air quality and is strictly regulated in many places
The acid sites of the molecular sieve catalyst are beneficial to3adsorption and activation of NH3, II −SSZ−13 catalysts are shown in temperature-programmed desorption
The CuII −SSZ−13 catalysts were prepared by in-situ hydrothermal synthesis method using various copper precursors (CuII (NO3 )2, CuII SO4, CuII Cl2 ) for NO selective catalytic reduction with NH3 in simulated diesel vehicle exhausts

Summary

Introduction

The emission of nitrogen oxides is a major cause of unhealthy air quality and is strictly regulated in many places. To meet regulations, controlling the emission of nitrogen oxides from diesel exhaust is one important topic in catalysis [1,2]. The core issue of this technology is the development of environmentally friendly SCR catalysts with high activity, wide operating temperature window, and excellent hydrothermal stability. Prior to the application of molecular sieve catalysts, NOx abatement technology relied primarily on. The CuII −SSZ−13 molecular sieve used as NH3 -SCR catalysts has become a hot topic due to its wide temperature window, high N2 selectivity, and excellent hydrothermal stability [7,8,9]. CuII −SSZ−13 shows its superiority in hydrothermal stability under moderate aging temperatures (e.g., 750–800 ◦ C) compared to other well-known Cu molecular sieves (e.g., Cu-ZSM-5, Cu-beta, and Cu-Y) [10]

Methods

Results

Conclusion