Cu/SSZ-13催化剂脱硝活性中心与催化性能构效关系的研究

doi:10.11949/0438-1157.20211230

摘要/Abstract

摘要：

NH₃选择性催化还原NO_x（NH₃-SCR）是目前最有应用前景的柴油车尾气净化技术，该技术的核心是开发具备优异催化性能的催化剂。以具有菱沸石（chabazite，CHA）结构的小孔分子筛SSZ-13为载体制备的Cu/SSZ-13催化剂，因具有优异的催化性能和水热稳定性能而受到广泛关注。制备了系列Cu_x/SSZ-13催化剂，并通过CO原位漫反射红外光谱（DRIFT）和H₂-TPR等方法能够确定具有高催化活性的铜离子在SSZ-13分子筛上的落位和存在状态。CO红外吸附实验发现，采用Cu(NO₃)₂水溶液离子交换法制备的Cu/SSZ-13催化剂上存在多种落位的Cu⁺活性中心。在较低的Cu⁺交换度条件下，Cu⁺优先落位于SSZ-13分子筛的八元环位置，随着交换度的提高，Cu⁺开始落位于SSZ-13分子筛双六元环的位置。H₂-TPR结果表明Cu_x/SSZ-13催化剂上也存在大量落位在八元环位置不稳定的Cu²⁺，这些Cu²⁺很容易被还原为Cu⁺。Cu_x/SSZ-13催化剂经800℃水蒸气连续老化16 h，分子筛骨架崩塌程度随着Cu含量的增加而提高，骨架铝的脱除，导致Cu物种发生团聚，而第二金属Ce元素的引入能够在一定程度上提高Cu/SSZ-13的水热稳定性。催化剂构效关系研究表明，具有一定量稳定存在的Cu⁺，并且拥有大量不稳定存在Cu²⁺的催化剂具有较宽温度范围的脱硝性能。

关键词: NH₃-SCR 反应, Cu/SSZ-13催化剂, 铜离子, 活性

Abstract:

Ammonia (NH₃) selective catalytic reduction of nitrogen oxides (NH₃-SCR) is currently the most promising diesel exhaust purification technology. The core of this technology is the development of catalysts with excellent catalytic performance. In recent years, Cu modified SSZ-13 zeolites with chabazite (CHA) topology as support have attracted extensive attention due to their excellent catalytic performance and hydrothermal stability. Therefore, in this study, a series of Cu_x/SSZ-13 catalysts with different Cu/Al ratios were prepared. The location and state of Cu ions on SSZ-13 zeolites with high catalytic activity was determined by insitu diffuse reflection infrared spectrum (DRIFT) using CO as probe molecule and H₂-TPR. By means of CO adsorption experiments, it was found that the Cu_x/SSZ-13 catalysts prepared by the ion exchange method of Cu(NO₃)₂ aqueous solution had a variety of Cu⁺ active sites. For catalysts with low Cu ion exchange degree, Cu⁺ firstly located in the micro-channel of SSZ-13 zeolites. As Cu exchange degree increased, Cu⁺ would locate in the double-six-membered ring of SSZ-13 zeolites. H₂-TPR characterization results show that there are also a large number of unstable Cu²⁺ located in the eight membered ring on Cu_x/SSZ-13 catalyst, which can be easily reduced to Cu⁺. For Cu/SSZ-13 catalyst aged by steam at 800℃ for 16 h, most of framework aluminum removed and Cu species agglomerated, both of which resulted in zeolites framework collapse. While, to a certain extent, the addition of Ce can improve the hydrothermal stability of Cu/SSZ-13 and protect the zeolites framework from collapse. The structure-activity relationship of the catalyst shows that the catalyst with a certain amount of stable Cu⁺ and a large amount of unstable Cu²⁺ has catalytic performance for NH₃-SCR in a wide temperature range.

Key words: NH₃-SCR reaction, Cu/SSZ-13 catalysts, Cu ion, reactivity

中图分类号:

TQ 028.8

周微, 王福烨, 贺宁, 于海斌, 马新宾, 刘家旭. Cu/SSZ-13催化剂脱硝活性中心与催化性能构效关系的研究[J]. 化工学报, 2022, 73(2): 672-680.

Wei ZHOU, Fuye WANG, Ning HE, Haibin YU, Xinbin MA, Jiaxu LIU. Study on the relationship of active centers and catalytic performance of Cu/SSZ-13 for NH₃-SCR[J]. CIESC Journal, 2022, 73(2): 672-680.

图/表 9

图1 Cu基催化剂的脱硝性能（反应条件：常压，GHSV=1.26×105 h-1）

Fig.1 Catalytic performance of Cu-based catalysts in NH3-SCR

表1 Cu基SSZ-13系列催化剂的氮气物理吸附计算结果

Table 1 N2 physical adsorption-desorption results of Cu-loaded SSZ-13 zeolites

Catalyst	BET/(m²/g)	S_g,mic /(m²/g)	S_g,extern /(m²/g)	V_pores /(cm³/g)	V_micro /(cm³/g)	V_meso/(cm³/g)
SSZ-13	653	619	34	0.32	0.27	0.05
Cu_0.44/SSZ-13	647	618	29	0.31	0.25	0.06
Cu_0.50/SSZ-13	646	617	29	0.30	0.25	0.05
Cu_0.58/SSZ-13	623	592	31	0.30	0.24	0.06
Ce_0.10Cu_0.44/SSZ-13	615	580	25	0.29	0.24	0.05
Ce_0.10Cu_0.50/SSZ-13	614	581	26	0.28	0.23	0.05
Cu_0.44/SSZ-13-st-800-16	404	379	25	0.21	0.16	0.05
Cu_0.50/SSZ-13-st-800-16	192	174	18	0.11	0.07	0.04
Cu_0.58/SSZ-13-st-800-16	87	74	13	0.07	0.05	0.02
Ce_0.10Cu_0.44/SSZ-13-st-800-16	466	434	32	0.25	0.19	0.06
Ce_0.10Cu_0.50/SSZ-13-st-800-16	372	344	28	0.18	0.14	0.04

图2 微米SSZ-13沸石分子筛的XRD谱图

Fig.2 XRD patterns of micro-sized SSZ-13 zeolite

图3 Cu基SSZ-13系列催化剂的红外羟基谱图

Fig.3 FT-IR spectra of hydroxyl groups on Cu-loaded SSZ-13 zeolites

图4 Cu/SSZ-13及CeCu/SSZ-13催化剂高温水蒸气钝化处理前后的红外羟基谱图

Fig.4 FT-IR spectra of hydroxyl groups on the sample Cu/SSZ-13 and CeCu/SSZ-13 (before and after steaming)

图5 原位漫反射红外光谱上以CO作为探针分子在Cu/SSZ-13催化剂上的吸附

Fig.5 In situ diffuse reflection infrared spectrum of CO adsorption on Cu/SSZ-13 catalysts

图6 Cu0.50/SSZ-13和Ce0.10Cu0.50/SSZ-13催化剂水热前后的CO吸附原位漫反射红外光谱

Fig.6 In situ diffuse reflection infrared spectrum of CO adsorption on Cu0.50/SSZ-13 and Ce0.10Cu0.50/SSZ-13 catalysts(before and after steaming)

图7 惰性气体吹扫后Cu/SSZ-13和CeCu/SSZ-13催化剂上CO吸附原位漫反射红外光谱

Fig.7 In situ diffuse reflection infrared spectrum of CO adsorption on Cu/SSZ-13 and CeCu/SSZ-13 catalysts in flowing of inert gas

图8 Cu基催化剂的H2-TPR谱图

Fig.8 H2-TPR profiles of Cu-basedcatalysts

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