Fe和Cu分子筛催化剂同时催化NOx还原和N2O分解

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摘要采用离子交换法制备了Fe-Beta和Cu-SSZ-13催化剂并采用不同混合方式制备了复合催化剂,考察了催化剂同时催化NO_x还原和N₂O分解的性能.以实现NO_x和N₂O同时高效去除、拓宽活性温度窗口为目标,优选出了上Fe下Cu分层填充、Fe-Beta和Cu-SSZ-13质量比为4:1的Fe_0.4Cu_0.1催化剂,进一步考察了进气组成对NO_x、N₂O和NH₃转化率的影响,并采用N₂吸脱附、XRD、NH3-TPD、UV-Vis DRS和H₂-TPR等手段对催化剂理化特性进行了表征.结果表明,Cu-SSZ-13和Fe-Beta分别具有更优的催化NO_x还原和N₂O分解性能.采用Fe0.4Cu0.1催化剂、[NH₃]/[NO_x]为1时考察的温度范围内NH₃仅还原NO_x,而N₂O通过分解去除,450℃时NO_x和N₂O转化率分别为93.4%和100%.高温(>350℃)下NH₃被O₂氧化导致NO_x转化率随温度升高而降低;高温(≥350℃)下N₂O分解形成的氧物种可使NO_x在进气中无O₂条件下实现高效还原.进气中含2% H₂O对高温(450℃)下Fe_0.4Cu_0.1表面NO_x的还原和NH₃的氧化无显著影响,但对N₂O的转化存在一定的可逆抑制作用.Cu-SSZ-13表面存在大量孤立的Cu²⁺离子,可为NH₃-SCR反应提供充足的活性中心.Fe-Beta表面同时存在能够催化NO氧化的孤立Fe³⁺离子和催化N₂O分解的Fe_xO_y物种.采用上Fe下Cu分层填充的混合方式时Fe-Beta表面NO氧化过程会消耗N₂O分解形成的氧物种,从而有利于低温(≤450℃)下N₂O的转化.但由于N₂O分解的温度范围内NO_x转化率本身较高,NO氧化对于脱硝的促进作用不显著.

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关键词 ： NO_x还原, N₂O分解, Fe-Beta, Cu-SSZ-13, 复合催化剂

Abstract：Fe-Beta and Cu-SSZ-13 catalysts were prepared by ion-exchange method, and composite catalysts were prepared using different mixing methods. Performance of the catalysts in catalyzing NO_x reduction and N₂O decomposition at the same time was investigated. Fe_0.4Cu_0.1catalyst, which was composed of Fe-Beta in the top layer and Cu-SSZ-13 in the bottom layer with mass ratio of 4:1, performed the best in catalyzing the removal of NO_x and N₂O simultaneously and broadening the reactive temperature window. Effects of inlet gas composition on the conversion of NO_x, N₂O, and NH₃ were investigated. Physicochemical characteristics of the catalysts were characterized by N₂ adsorption-desorption, XRD, NH₃-TPD, UV-Vis DRS and H₂-TPR techniques. The results showed that Cu-SSZ-13 and Fe-Beta had superior performance in catalyzing NO_x reduction and N₂O decomposition, respectively. In the tested temperature range, NO_x was reduced by NH₃ while N₂O was decomposed over Fe_0.4Cu_0.1 when [NH₃]/[NO_x] was 1. NO_x and N₂O conversion reached 93.4% and 100%, respectively at 450℃. Oxidation of NH₃ by O₂ at high temperatures (>350℃) leads to decrease in NO_x conversion with increasing temperature. And the formation of oxygen species from the decomposition of N₂O at high temperatures (≥350℃) explains the efficient NO_x reduction without O₂ in the inlet gas. The presence of 2%H₂O in the inlet gas hardly affected the reduction of NO_x and oxidation of NH₃ over Fe_0.4Cu_0.1 at high temperature (450℃), but did show reversible inhibitory effects on the conversion of N₂O. Abundant isolated Cu²⁺ ions were detected over Cu-SSZ-13, providing sufficient active centers for the NH₃-SCR reaction. Both isolated Fe³⁺ ions and Fe_xO_y species, which can catalyze NO oxidation and N₂O decomposition, respectively, were detected over Fe-Beta. Using the top-Fe-bottom-Cu composite catalyst, NO oxidation occurs over Fe-Beta, which consumes oxygen species formed from N₂O decomposition and thus promotes the conversion of N₂O at low temperatures (≤450℃). However, the promotion effect of NO oxidation on NO_x reduction was insignificant since NO_x conversion was rather high in the temperature range for effective N₂O decomposition.

Key words： NO_x reduction N₂O decomposition Fe-Beta Cu-SSZ-13 composite catalyst

收稿日期: 2024-02-09

PACS:

X511

基金资助:国家自然科学基金资助项目(21707004);北京市自然科学基金资助项目(8152011)

通讯作者: 樊星,副教授,fanxing@bjut.edu.cn E-mail: fanxing@bjut.edu.cn

作者简介: 司庆宇(1997-),男,河北廊坊人,北京工业大学硕士研究生,主要从事大气污染控制工程研究.发表论文1篇.siqingyuqz@163.com.

引用本文:

司庆宇, 樊星, 张玮航, 苗静文, 刘若雯. Fe和Cu分子筛催化剂同时催化NO_x还原和N₂O分解[J]. 中国环境科学, 2024, 44(9): 4826-4834. SI Qing-yu, FAN Xing, ZHANG Wei-hang, MIAO Jing-wen, LIU Ruo-wen. Simultaneous reduction of NO_x and decomposition of N₂O over Fe and Cu zeolite catalysts. CHINA ENVIRONMENTAL SCIENCECE, 2024, 44(9): 4826-4834.

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http://www.zghjkx.com.cn/CN/ 或 http://www.zghjkx.com.cn/CN/Y2024/V44/I9/4826

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