了解用于低温 NH3-SCR 的氧化锰-沸石杂化催化剂上的布氏/路易斯酸位点的作用

IF 15.7 1区 化学 Q1 CHEMISTRY, APPLIED
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Systematic <em>in situ</em> diffuse reflectance infrared Fourier transform spectroscopy analyses coupled with selective catalytic reduction of NO<sub><em>x</em></sub> with NH<sub>3</sub> (NH<sub>3</sub>-SCR) reaction demonstrate that the Lewis acid sites over MnO<sub><em>x</em></sub> are more active for NO reduction but have lower selectivity to N<sub>2</sub> than Brønsted acids sites. Brønsted acid sites primarily produce N<sub>2</sub>, whereas Lewis acid sites primarily produce N<sub>2</sub>O, contributing to unfavorable N<sub>2</sub> selectivity. The Brønsted acid sites present in Y zeolite, which are stronger than those on MnO<sub><em>x</em></sub>, accelerate the NH<sub>3</sub>-SCR reaction in which the nitrite/nitrate species diffused from the MnO<sub><em>x</em></sub> particles rapidly convert into the N<sub>2</sub>. 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引用次数: 0

摘要

尽管人们早已知道金属氧化物-沸石杂化材料可以通过中间产物的颗粒间扩散来提高氮氧化物去除反应的催化活性和选择性,但其在酸性位点上的后续反应机制仍不清楚,需要进行研究。在本研究中,通过引入钾离子精确调整了杂化材料中的布氏/刘易斯酸位点分布,钾离子不仅能选择性地与布氏酸位点结合,还可能影响活化 NO 物种的形成和扩散。系统的原位漫反射红外傅立叶变换光谱分析以及选择性催化还原氮氧化物与 NH3(NH3-SCR)反应表明,MnOx 上的路易斯酸位点对还原氮氧化物的活性更高,但对 N2 的选择性低于布氏酸位点。布氏酸性位点主要产生 N2,而路易斯酸性位点主要产生 N2O,从而导致对 N2 的选择性降低。Y 沸石中的布氏硬度酸比 MnOx 上的布氏硬度酸更强,从而加速了 NH3-SCR 反应,在该反应中,从 MnOx 颗粒扩散的亚硝酸盐/硝酸盐迅速转化为 N2。因此,重要的是设计催化剂,使 MnOx 中形成的活化 NO 物种扩散到 H-Y 沸石的布氏酸位点而不是 MnOx 颗粒的布氏酸位点,并在这些位点上选择性地分解。对于物理混合的 H-MnOx+H-Y 样品,H-MnOx 中丰富的布氏/路易斯酸位点会在活化的 NO 物种在颗粒间扩散之前大量消耗,从而阻碍协同效应的增强。此外,我们还发现,K-MnOx 中的插层 K+ 在氮氧化物还原速率中起到了意想不到的有利作用,这可能是由于活化的氮氧化物物种在 K-MnOx 上的扩散速度快于 H-MnOx。这项研究通过确定两种不同成分中酸性位点的作用,有助于设计出有前途的金属氧化物-沸石杂化催化剂。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Understanding the roles of Brønsted/Lewis acid sites on manganese oxide-zeolite hybrid catalysts for low-temperature NH3-SCR
Although metal oxide-zeolite hybrid materials have long been known to achieve enhanced catalytic activity and selectivity in NOx removal reactions through the inter-particle diffusion of intermediate species, their subsequent reaction mechanism on acid sites is still unclear and requires investigation. In this study, the distribution of Brønsted/Lewis acid sites in the hybrid materials was precisely adjusted by introducing potassium ions, which not only selectively bind to Brønsted acid sites but also potentially affect the formation and diffusion of activated NO species. Systematic in situ diffuse reflectance infrared Fourier transform spectroscopy analyses coupled with selective catalytic reduction of NOx with NH3 (NH3-SCR) reaction demonstrate that the Lewis acid sites over MnOx are more active for NO reduction but have lower selectivity to N2 than Brønsted acids sites. Brønsted acid sites primarily produce N2, whereas Lewis acid sites primarily produce N2O, contributing to unfavorable N2 selectivity. The Brønsted acid sites present in Y zeolite, which are stronger than those on MnOx, accelerate the NH3-SCR reaction in which the nitrite/nitrate species diffused from the MnOx particles rapidly convert into the N2. Therefore, it is important to design the catalyst so that the activated NO species formed in MnOx diffuse to and are selectively decomposed on the Brønsted acid sites of H-Y zeolite rather than that of MnOx particle. For the physically mixed H-MnOx+H-Y sample, the abundant Brønsted/Lewis acid sites in H-MnOx give rise to significant consumption of activated NO species before their inter-particle diffusion, thereby hindering the enhancement of the synergistic effects. Furthermore, we found that the intercalated K+ in K-MnOx has an unexpected favorable role in the NO reduction rate, probably owing to faster diffusion of the activated NO species on K-MnOx than H-MnOx. This study will help to design promising metal oxide-zeolite hybrid catalysts by identifying the role of the acid sites in two different constituents.
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来源期刊
Chinese Journal of Catalysis
Chinese Journal of Catalysis 工程技术-工程:化工
CiteScore
25.80
自引率
10.30%
发文量
235
审稿时长
1.2 months
期刊介绍: The journal covers a broad scope, encompassing new trends in catalysis for applications in energy production, environmental protection, and the preparation of materials, petroleum chemicals, and fine chemicals. It explores the scientific foundation for preparing and activating catalysts of commercial interest, emphasizing representative models.The focus includes spectroscopic methods for structural characterization, especially in situ techniques, as well as new theoretical methods with practical impact in catalysis and catalytic reactions.The journal delves into the relationship between homogeneous and heterogeneous catalysis and includes theoretical studies on the structure and reactivity of catalysts.Additionally, contributions on photocatalysis, biocatalysis, surface science, and catalysis-related chemical kinetics are welcomed.
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