Influence of Solvent on Selective Catalytic Reduction of Nitrogen Oxides with Ammonia over Cu-CHA Zeolite.
Influence of Solvent on Selective Catalytic Reduction of Nitrogen Oxides with Ammonia over Cu-CHA Zeolite.
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DOI：
10.1021/jacs.2c09823
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发表时间：
2023-01-11
影响因子：
15
通讯作者：
Sokol, Alexey A.
中科院分区：
文献类型：
--
作者：
Nasir, Jamal Abdul;Guan, Jingcheng;Keal, Thomas W.;Desmoutier, Alec W.;Lu, You;Beale, Andrew M.;Catlow, C. Richard A.;Sokol, Alexey A.
近年来，铜交换分子筛CuCHA因其在NOx选择性催化还原(SCR)中的应用而备受关注。在这里，我们用量子力学/分子力学混合(QM/MM)技术研究了NH_3-SCR在铜-CHA上的反应机理，并考察了溶剂对活性铜物种反应活性的影响。为此，比较了水溶剂化、氨溶剂化和裸铜物种。结果表明，溶剂对NH3-SCR循环中氧化组分的促进作用是因为在溶剂化的铜位上形成重要的硝酸盐物种比在没有溶剂分子的情况下更有利。相反，预计这两种溶剂分子都会抑制NH3-SCR循环的还原成分。利用(浓度)调制激发光谱(MES)和相敏检测(PSD)的漫反射红外傅里叶变换光谱(DRIFTS)实验确定了以前未在实验中观察到的重要物种--硝酸铜和亚硝胺的光谱特征。这进一步得到了QM/MM计算的简谐振动分析的支持。对溶剂化活性中心的反应性和关键中间体的形成，包括它们的形成能和振动光谱特征，提供了更多的见解，使我们能够对反应机理有一个详细的了解。我们展示了溶剂化活性中心的作用及其对重要物种的能量学的影响，这必须被明确地考虑以准确地理解NH3-SCR动力学。
The copper-exchanged zeolite Cu-CHA has received considerable attention in recent years, owing to its application in the selective catalytic reduction (SCR) of NOx species. Here, we study the NH3-SCR reaction mechanism on Cu-CHA using the hybrid quantum mechanical/molecular mechanical (QM/MM) technique and investigate the effects of solvent on the reactivity of active Cu species. To this end, a comparison is made between water- and ammonia-solvated and bare Cu species. The results show the promoting effect of solvent on the oxidation component of the NH3-SCR cycle since the formation of important nitrate species is found to be energetically more favorable on the solvated Cu sites than in the absence of solvent molecules. Conversely, both solvent molecules are predicted to inhibit the reduction component of the NH3-SCR cycle. Diffuse reflectance infrared fourier-transform spectroscopy (DRIFTS) experiments exploiting (concentration) modulation excitation spectroscopy (MES) and phase-sensitive detection (PSD) identified spectroscopic signatures of Cu-nitrate and Cu-nitrosamine (H2NNO), important species which had not been previously observed experimentally. This is further supported by the QM/MM-calculated harmonic vibrational analysis. Additional insights are provided into the reactivity of solvated active sites and the formation of key intermediates including their formation energies and vibrational spectroscopic signatures, allowing the development of a detailed understanding of the reaction mechanism. We demonstrate the role of solvated active sites and their influence on the energetics of important species that must be explicitly considered for an accurate understanding of NH3-SCR kinetics.
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