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Improvement of catalyst for selective reduction of NO by controlling reaction atmospheres

通过控制反应气氛改进NO选择性还原催化剂

基本信息

批准号：
14350425
负责人：
SATSUMA Atsushi
金额：
$ 9.09万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-14350425/
关键词：
NOx Selective Reduction Catalyst Reaction atmospheres Reaction mechanism in-situ spectroscopy Dynamics of active species Diesel engine

项目摘要

The addition of hydrogen in the reaction atmosphere is effective in promoting the activity of Ag/alumina and Ag-zeolites on the selective reduction of NO by hydrocarbons (HC-SCR) at low temperatures. The increment of NO conversion over Ag-MFI corresponds to the periodic addition of hydrogen into C_3H_8-SCR conditions. The UV-Vis spectra of Ag-MFI have revealed that the addition of hydrogen results in the formation of Ag_n^<□+> clusters due to partial reduction and agglomeration of Ag species The coincidence of the formation of the Ag_n^<□+> clusters and the increment of NO conversion suggests that Ag_n^<□+> clusters are the highly active species for HC-SCR. From analysis by H_2-TPR, UV-Vis, and EXAFS, the structure of Ag_n^<□+> clusters on Ag-MFI is identified as being Ag_4^<2+> on average. The formation of Ag clusters was strongly affected by the type of zeolites : The major Ag species are Ag^+ ions for MOR, Ag_n^<□+> clusters for MFI and BEA, and relatively large metallic Ag_m particles for Y. The sequence of Ag agglomeration (MOR<MFI<BEA<Y) is in accordance with the strength of the acid sites of zeolites. It can be expected that the interaction between the positive charge of Ag_n^<□+> clusters and acid sites, i.e., the ion-exchange site of zeolites, stabilizes Ag_n^<□+> clusters. The type of Ag species under HC-SCR conditions depends on the concentration of gas-phase oxidants (NO,O_2) and reductants (H_2,HC), and also on the number and strength of the zeolite acid sites.

在反应气氛中添加氢气可以有效地促进Ag/氧化铝和Ag-沸石在低温下通过烃选择性还原NO（HC-SCR）的活性。在Ag-MFI催化剂上，NO转化率的增加对应于在C_3H_8-SCR条件下周期性地添加氢气。紫外-可见吸收光谱表明，氢气的加入使Ag原子团簇部分还原并聚集形成Ag_n^<□+>团簇，Ag_n^<□+>团簇的形成与NO转化率的增加相一致，表明Ag_n^<□+>团簇是HC-SCR的高活性物种。通过H_2-TPR、UV-Vis和EXAFS分析，确定了Ag-MFI上Ag_n^<□+>团簇的平均结构为Ag_4 ^<2+>。Ag团簇的形成受沸石类型的强烈影响：对于莫尔，主要的Ag物种是Ag^+离子，对于MFI和Al 2 O3，主要的Ag物种是Ag_n <□+>团簇，而对于Y，主要的Ag物种是较大的金属Ag_m颗粒。Ag的团聚顺序（莫尔比<MFI<X <Y）与分子筛的酸中心强度一致。可以预期，Ag_n^<□+>簇合物的正电荷与酸中心之间的相互作用，即，沸石的离子交换位稳定Ag_n^<□+>团簇。HC-SCR条件下Ag物种的类型取决于气相氧化剂（NO、O_2）和还原剂（H_2、HC）的浓度以及沸石酸中心的数量和强度。