Improving the NOx decomposition and storage activity through co-incorporating ammonium and copper ions into Mg/Al hydrotalcites

Shuhua Zhang; Weijun Liu; Cheng Wang; Chenhui Zhu; Siyuan Yang; Minghua Guo; Ruimin Qiao; Polite Stewart; Hongmei Zhang; Xiaodan Gu; Alexander Hexemer; Yayu Wang; Wanli Yang

doi:10.1039/C6RA06665H

Improving the NO_x decomposition and storage activity through co-incorporating ammonium and copper ions into Mg/Al hydrotalcites

Shuhua Zhang,*^a Weijun Liu,^b Cheng Wang,^c Chenhui Zhu,^c Siyuan Yang,^a Minghua Guo,^cd Ruimin Qiao,^c Polite Stewart,^c Hongmei Zhang,^a Xiaodan Gu,^e Alexander Hexemer,^c Yayu Wang^d and Wanli Yang^c

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* Corresponding authors

^a College of Chemistry and Chemical Engineering, Shanghai University of Engineering Science, Shanghai 201620, China
E-mail: zsh_7474@126.com, Zhangsh@sues.edu.cn
Tel: +86-13916737957

^b College of Mechanical Engineering, Shanghai University of Engineering Science, Shanghai 201620, China

^c Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

^d State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China

^e Department of Chemical Engineering, Stanford University, Menlo Park, CA, USA

Abstract

We report a 40% and 70% improvement of NO_x decomposition and storage rate based on synthetic Mg/Al/Cu/NH₄⁺ hydrotalcites (HT), compared with Mg/Al/NH₃ and Mg/Al/Cu HTs. TGA and DTG show that ammonium has been released from HT below 160 °C. A combined characterization through WAXS (Wide-Angle X-ray Scattering), SEM, sXAS (soft X-ray Absorption Spectroscopy), CHNS elemental analysis and N₂ absorption and desorption reveals the structural and physical properties of this co-incorporated system. While Mg/Al/Cu/NH₄⁺ HT retains the typical structure of hydrotalcite-like compounds, its crystallinity weakened. WAXS shows that the layer–layer spacing of Mg/Al/Cu and Mg/Al/Cu/NH₄⁺ HTs decreases due to the Jahn–Teller effect. The particle size of Mg/Al/Cu/NH₄⁺ decreases about 10 nm compared with that of Mg/Al/Cu HT. sXAS and CHNS elemental analysis reveal that ammonium was successfully introduced into Mg/Al/Cu/NH₄⁺ HT by analyzing the N-K edge and CHN content, but not into HT without Cu²⁺, indicating the importance of the co-incorporation of ammonium and Cu²⁺. Additionally, the test of NO_x decomposition and storage activity revealed that the introduction of ammonium into the system should be responsible for the performance improvement.

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Improving the NO_x decomposition and storage activity through co-incorporating ammonium and copper ions into Mg/Al hydrotalcites

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Improving the NO_x decomposition and storage activity through co-incorporating ammonium and copper ions into Mg/Al hydrotalcites

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