In this Review, we discuss the state-of-the-art understanding of non-precious transition metal oxides that catalyze the oxygen reduction and evolution reactions. Understanding and mastering the kinetics of oxygen electrocatalysis is instrumental to making use of photosynthesis, advancing solar fuels, fuel cells, electrolyzers, and metal–air batteries. We first present key insights, assumptions and limitations of well-known activity descriptors and reaction mechanisms in the past four decades. The turnover frequency of crystalline oxides as promising catalysts is also put into perspective with amorphous oxides and photosystem II. Particular attention is paid to electronic structure parameters that can potentially govern the adsorbate binding strength and thus provide simple rationales and design principles to predict new catalyst chemistries with enhanced activity. We share new perspective synthesizing mechanism and electronic descriptors developed from both molecular orbital and solid state band structure principles. We conclude with an outlook on the opportunities in future research within this rapidly developing field.

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Toward the rational design of non-precious transition metal oxides for oxygen electrocatalysis

Automotive catalytic converters: current status and some perspectives

Nanostructured oxides in chemistry: characterization and properties.

Over the last several years, nitrogen oxide(s) (NOx) storage/reduction (NSR) catalysts, also referred to as NOx adsorbers or lean NOx traps, have been developed as an aftertreatment technology to reduce NOx emissions from lean‐burn power sources. NSR operation is cyclic: during the lean part of the cycle, NOx are trapped on the catalyst; intermittent rich excursions are used to reduce the NOx to N2 and restore the original catalyst surface; and lean operation then resumes. This review will describe the work carried out in characterizing, developing, and understanding this catalyst technology for application in mobile exhaust‐gas aftertreatment. The discussion will first encompass the reaction process fundamentals, which include five general steps involved in NOx reduction to N2 on NSR catalysts; NO oxidation, NO2 and NO sorption leading to nitrite and nitrate species, reductant evolution, NOx release, and finally NOx reduction to N2. Major unresolved issues and questions are listed at the end of ...

Overview of the Fundamental Reactions and Degradation Mechanisms of NOx Storage/Reduction Catalysts

Trends in NOx abatement: A review

X-ray absorption fine structure analysis of local structure of CeO2–ZrO2 mixed oxides with the same composition ratio (Ce/Zr=1)

This paper reviews progress in the development of oxygen storage materials for automotive exhaust catalysts. The research was mainly conducted as a study and development exercise in the author's laboratory in Japan. Ceria-lanthana solid solutions (CL) and the first generation of ceriazirconia solid solutions (CZ) were developed as excellent oxygen storage materials for automotive catalysts in the 1980s. These materials consist of ceria doped with less than 20 mol% of La4+ or Zr4+. An increase in oxygen defects in CL and CZ under reductive conditions is responsible for an enhanced oxygen storage capability on the cerium atoms. An accurate measure of the oxygen storage capacity (OSC) per cerium is very important for theoretical and practical treatments of the catalyst. The term “partial OSC” was introduced to describe this capacity and to differentiate it from the usual definition of the OSC, known also as the “total OSC”. After the development of CL and CZ, a new technology was developed to dissolve more than 20 mol% of zirconia in the ceria, allowing second generation CZ and third generation CZ (known as ACZ, which is doped with alumina) to be successfully developed in the 1990s. The partial OSC of these materials increases with increasing amounts of zirconia dissolved in the ceria, and also with decreasing material particle size after an engine durability test. In the case of ACZ, alumina was added to CZ based on the “diffusion barrier concept”, in which a diffusion barrier layer inhibits the coagulation of CZ and A when the material is required for duty at high temperature in air. Furthermore, the relationship between the total or partial OSC and the structure of the ceriazirconia solid solutions is explained in this paper. For ceriazirconia solid solutions composed of equimolar CeO2 and ZrO2(Ce/Zr=1), the total or partial OSC of the κ-phase CeZrO4, in which the cerium and zirconium ions are regularly distributed, was about twice as large as that of a ceriazirconia solid solution with a relatively irregular distribution of cerium and zirconium ions, and about five times larger than that of a mixture of ceria powder and zirconia containing only a small amount of ceriazirconia solid solution. It corresponds to about 89% of the theoretical maximum value. For a ceriazirconia solid solution composed of non-equimolar CeO2 and ZrO2(Ce/Zr ≠ 1), the partial OSC of a ceria-κ-phase solid solution with a zirconia content of between 30 and 50mol% is much higher than that of a ceriazirconia solid solution of the same zirconia content. The partial OSC of a κ-phase and zirconia mixed oxide, which is formed by reducing the material at 1200 °C, reaches a value above 0.20 mol-O2/mol-Ce (about 80% of the theoretical maximum value of the partial OSC), when the zirconia content is between 50 and 80 mol%. The Toyota Motor Corp. has put automotive three-way catalysts containing the first, second and third generations of CZ into practical use on a global basis.

Oxygen Storage Materials for Automotive Catalysts: Ceria-Zirconia Solid Solutions

Development of New Concept Three-Way Catalyst for Automotive Lean-Burn Engines

Innovative three-way catalysts containing ceria-zirconia solid solutions (CZ) with a ZrO 2 content ranging from 5 to 75 mol% were developed Such catalysts have very high oxygen storage/release capacity (OSC) The OSC of'catalysts containing first-generation CZ was found to increase linearly with the amount of zirconia dissolved in the solid solution in the 0-20 mol%( ZrO 2 range The thermal stability of the catalyst containing first-generation CZ was higher than that containing ceria Second-generation CZ with greater OSC than first-generation CZ was developed by a homogeneous coprecipitation process, followed by heat-treatment below 1000 °C, enabling dissolution of zirconia into ceria up to 75 mol% zirconia as estimated by XRD Third-generation CZ, CZ-doped alumina (ACZ), was developed by homogeneous coprecipitation based on the "diffusion barrier concept" The OSC of ACZ was 23 times larger than that of pure ceria The NOx emission over the catalyst containing ACZ was reduced by about a factor of five compared with that containing pure ceria Toyota Motor Corp has put three-way catalysts containing first-, second-, and third-generation CZ into practical use globally

Development of Innovative Three-Way Catalysts Containing Ceria–Zirconia Solid Solutions with High Oxygen Storage/Release Capacity

The NO x storage-reduction catalysis under oxidizing conditions in the presence of SO 2 has been investigated on Pt/Ba/Fe/Al 2 O 3 , Pt/Ba/Co/Al 2 O 3 , Pt/Ba/Ni/Al 2 O 3 , and Pt/Ba/Cu/Al 2 O 3 catalysts compared with Pt/Ba/Al 2 O 3 , Pt/Fe/Al 2 O 3 , Pt/Co/Al 2 O 3 , Pt/Ni/Al 2 O 3 , Pt/Cu/Al 2 O 3 and Pt/Al 2 O 3 catalysts. The NO x purification activity of Pt/Ba/Fe/Al 2 O 3 catalyst was the highest of all the catalysts investigated in this paper after an aging treatment. That of the aged Pt/Ba/Co/Al 2 O 3 and Pt/Ba/Ni/Al 2 O 3 catalysts was essentially the same as that of the aged Pt/Ba/Al 2 O 3 catalyst, while that of the aged Pt/Ba/Cu/Al 2 O 3 and Pt/Cu/Al 2 O 3 catalysts was substantially lower than the others. The Fe-compound on the aged Pt/Ba/Fe/Al 2 O 3 catalyst has played a role in decreasing the sulfur content on the catalyst after exposure to simulated reducing gas compared with the Pt/Ba/Al 2 O 3 catalyst without the Fe-compound. XRD and EDX show that the Fe-compound inhibits the growth in the size of BaSO 4 particles formed on the Pt/Ba/Fe/Al 2 O 3 catalyst under oxidizing conditions in the presence of SO 2 and promotes the decomposition of BaSO 4 and desorption of the sulfur compound under reducing conditions.

Effect of the addition of transition metals to Pt/Ba/Al2O3 catalyst on the NOx storage-reduction catalysis under oxidizing conditions in the presence of SO2

Masahiro Sugiura

Papers

X-ray absorption fine structure analysis of local structure of CeO2–ZrO2 mixed oxides with the same composition ratio (Ce/Zr=1)

Oxygen Storage Materials for Automotive Catalysts: Ceria-Zirconia Solid Solutions

Development of New Concept Three-Way Catalyst for Automotive Lean-Burn Engines

Development of Innovative Three-Way Catalysts Containing Ceria–Zirconia Solid Solutions with High Oxygen Storage/Release Capacity

Effect of the addition of transition metals to Pt/Ba/Al2O3 catalyst on the NOx storage-reduction catalysis under oxidizing conditions in the presence of SO2