Copper-Iron Bimetal Ion-Exchanged SAPO-34 for NH3-SCR of NOx

Tuan Doan,Thanh Huyen Pham,Phong Dam,Khang Nguyen,Thanh Huyen Vuong,Minh Thang Le

doi:10.3390/catal10030321

Abstract

SAPO-34 was prepared with a mixture of three templates containing triethylamine, tetraethylammonium hydroxide, and morpholine, which leads to unique properties for support and production cost reduction. Meanwhile, Cu/SAPO-34, Fe/SAPO-34, and Cu-Fe/SAPO-34 were prepared through the ion-exchanged method in aqueous solution and used for selective catalytic reduction (SCR) of NOx with NH3. The physical structure and original crystal of SAPO-34 are maintained in the catalysts. Cu-Fe/SAPO-34 catalysts exhibit high NOx conversion in a broad temperature window, even in the presence of H2O. The physicochemical properties of synthesized samples were further characterized by various methods, including XRD, FE-SEM, EDS, N2 adsorption-desorption isotherms, UV-Vis-DRS spectroscopy, NH3-TPD, H2-TPR, and EPR. The best catalyst, 3Cu-1Fe/SAPO-34 exhibited high NOx conversion (> 90%) in a wide temperature window of 250–600 °C, even in the presence of H2O. In comparison with mono-metallic samples, the 3Cu-1Fe/SAPO-34 catalyst had more isolated Cu2+ ions and additional oligomeric Fe3+ active sites, which mainly contributed to the higher capacity of NH3 and NOx adsorption by the enhancement of the number of acid sites as well as its greater reducibility. Therefore, this synergistic effect between iron and copper in the 3Cu-1Fe/SAPO-34 catalyst prompted higher catalytic performance in more extensive temperature as well as hydrothermal stability after iron incorporation.

Highlights

Despite the advantages of good fuel economy and high-power density, modern diesel engines working under lean combustion conditions release several types of air pollutants, including carbon oxides (COx ), sulfur oxides (SOx ), volatile organics (VOCs), and especially nitrogen oxides
The structure of catalysts investigated by the X-ray powder diffraction (XRD) method presented in Figure 1 shows that the characteristic properties of the prepared Cu/SAPO-34, Fe/SAPO-34, and Cu-Fe/SAPO-34 samples nearly coincide with as-prepared SAPO-34 sample
This confirms that all catalysts are similar to the typical chabazite structure of SAPO-34 reported previously [30], indicating that the typical structure of SAPO-34 was maintained during the aqueous ion-exchange process

Summary

Introduction

Despite the advantages of good fuel economy and high-power density, modern diesel engines working under lean combustion conditions release several types of air pollutants, including carbon oxides (COx ), sulfur oxides (SOx ), volatile organics (VOCs), and especially nitrogen oxides. Those negative effects have drawn remarkable attention for researchers to figure out a solution to control NOx concentration, from diesel engines exhaust. When it comes to NOx reduction technologies, selective catalytic reduction of NOx by ammonia (NH3 -SCR) is commonly considered to have the highest efficiency for NOx treatment from diesel engines. The exhaust fume can meet current tightening emission standards, such as European Emission Standards

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