プラチナ基の金属に対するNO削減の段階的な選択性
Zhi-Pan Liu1, Stephen J Jenkins, David A King
1Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.
Journal of the American Chemical Society
|December 4, 2003
まとめ
ステップされたイリジウム (Ir) 表面は,窒素酸化物 (NO) の還元による窒素 (N2) 生産に対する高い選択性を示しています. この発見は,車両の排出量を制御し,触媒プロセスを理解するために極めて重要です.
科学分野:
- カタリシス カタリシス カタリシス
- 表面科学とは,地表科学である.
- 環境化学 環境化学
背景:
- 窒素酸化物 (NO) を窒素 (N2) に還元することは,車両の排出量管理に極めて重要です.
- プラチナ群の金属は重要な触媒ですが,その性能は表面構造によって異なります.
- NOの減少選択性を理解することは,効率的な触媒の開発に不可欠です.
研究 の 目的:
- イリジウム (Ir) とプラチナ (Pt) の表面でのNO還元の選択性を調査する.
- IrとPtの平面と段差のある表面の性能を比較するために.
- NO削減の選択性および活動を支配する要因を解明する.
主な方法:
- 第一原理 密度関数理論 (DFT) 計算.密度関数理論 (DFT) 計算.
- IrとPtの表面でのNO吸収と反応経路のシミュレーション.
- 触媒表面の電子構造と幾何学的構造の分析.
主要な成果:
- 段差のIr表面は,NOをN2に還元するための高い選択性を示しています.
- ステップされたIrの高い選択性は,そのユニークな電子と幾何学的構造と関連しています.
- ステップされたPt表面は,N2の選択性が低く,N2Oの生産を好みます.
- 過剰なO2下での金属および構造に依存するNOの減少行動が観察された.
結論:
- ステップされたIr表面は,排気制御における選択的なNO削減に有望である.
- カタリストの設計は,最適な性能のために電子的および幾何学的要因の両方を考慮する必要があります.
- DFTは,構造に敏感な触媒反応に関する貴重な洞察を提供します.
関連する概念動画
Formation of Complex Ions
A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...
Metal-Ligand Bonds
The hemoglobin in the blood, the chlorophyll in green plants, vitamin B-12, and the catalyst used in the manufacture of polyethylene all contain coordination compounds. Ions of the metals, especially the transition metals, are likely to form complexes.
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
Properties of Organometallic Compounds
Organometallic compounds are compounds that contain a carbon–metal bond. Carbon belongs to an organyl group like alkyl, aryl, allyl, or benzyl groups. The metal can be from Group I or Group II of the periodic table, a transition metal, or a semimetal.
Colloidal precipitates
The high insolubility of some precipitates can result in an unfavorable relative supersaturation. This can lead to colloidal particles with a large surface-to-mass ratio, where adsorption is promoted. For instance, in the precipitation of silver chloride, silver ions are adsorbed on the surface of the colloidal particles, forming a primary layer. This layer attracts ions of opposite charge (such as nitrate ions), forming a diffuse secondary layer of adsorbed ions. This electric double layer...
Extraction: Advanced Methods
Metal ions can be separated from one another by complexation with organic ligands–the chelating agent– to form uncharged chelates. Here, the chelating agent must contain hydrophobic groups and behave as a weak acid, losing a proton to bind with the metal. Since most organic ligands used in this process are insoluble or undergo oxidation in the aqueous phase, the chelating agent is initially added to the organic phase and extracted into the aqueous phase. The metal-ligand complex is formed in...
Complexation Equilibria: Factors Influencing Stability of Complexes
In complexation reactions, metal cations are the electron pair acceptors, and the ligands are the electron pair donors. The stability of the metal complexes depends primarily on the complexing ability of the central metal ion and the nature of the ligands. Generally, the complexing ability of the metal ion depends on the size and charge of the ion. As the metal ion size increases, the stability of the metal complexes decreases, provided that the valency of the metal ion and the ligands remain...


