2023-09-14 パシフィック・ノースウェスト国立研究所(PNNL)
◆NOxは主に燃焼エンジン車両や機械から排出される窒素酸化物で、以前は都市の空気や健康に影響を与えていた。近年は、クリーンな燃焼エンジン技術と排気後処理の導入により、これらの排出量は大幅に削減されてきた。
◆しかし、電動化が進む中でも農業など電動化が難しい分野からの排出は未解決の課題であり、効率的な触媒反応を進化させることが困難になっている。この研究により、酸度がディーゼル車の排出に影響を与え、効果的な触媒反応の鍵を示唆している。
＜関連情報＞
- https://www.pnnl.gov/news-media/reduced-nitrogen-oxide-emissions-industrial-vehicles-ahead
- https://www.nature.com/articles/s41467-023-38309-8
低温NH3-SCRにおける銅の酸化還元と移動、担体の酸性度とトポロジーの相互作用 Interplay between copper redox and transfer and support acidity and topology in low temperature NH3-SCR
Yiqing Wu,Wenru Zhao,Sang Hyun Ahn,Yilin Wang,Eric D. Walter,Ying Chen,Miroslaw A. Derewinski,Nancy M. Washton,Kenneth G. Rappé,Yong Wang,Donghai Mei,Suk Bong Hong & Feng Gao
Nature Communications Published:06 May 2023
DOI:https://doi.org/10.1038/s41467-023-38309-8
Abstract
Low-temperature standard NH3-SCR over copper-exchanged zeolite catalysts occurs on NH3-solvated Cu-ion active sites in a quasi-homogeneous manner. As key kinetically relevant reaction steps, the reaction intermediate CuII(NH3)4 ion hydrolyzes to CuII(OH)(NH3)3 ion to gain redox activity. The CuII(OH)(NH3)3 ion also transfers between neighboring zeolite cages to form highly reactive reaction intermediates. Via operando electron paramagnetic resonance spectroscopy and SCR kinetic measurements and density functional theory calculations, we demonstrate here that such kinetically relevant steps become energetically more difficult with lower support Brønsted acid strength and density. Consequently, Cu/LTA displays lower Cu atomic efficiency than Cu/CHA and Cu/AEI, which can also be rationalized by considering differences in their support topology. By carrying out hydrothermal aging to eliminate support Brønsted acid sites, both CuII(NH3)4 ion hydrolysis and CuII(OH)(NH3)3 ion migration are hindered, leading to a marked decrease in Cu atomic efficiency for all catalysts.
