Abstract
Automotive Three-Way Catalysts (TWC) were introduced more than 40 years ago. Despite that, the development of a sustainable TWC still remains a critical research topic owing to the increasingly stringent emission regulations together with the price and scarcity of precious metals. Among other material classes, perovskite-type oxides are known to be valuable alternatives to conventionally used TWC compositions and have demonstrated to be suitable for a wide range of automotive applications, ranging from TWC to Diesel Oxidation Catalysts (DOC), from NOx Storage Reduction catalysts (NSR) to soot combustion catalysts. The interest in these catalysts has been revitalized in the past ten years by the introduction of the concept of catalyst regenerability of perovskite-based TWC, which is in principle well applicable to other catalytic processes as well, and by the possibility to reduce the amounts of critical elements, such as precious metals without seriously lowering the catalytic performance. The aim of this review is to show that perovskite-type oxides have the potential to fulfil the requirements (high activity, stability, and possibility to be included into structured catalysts) for implementation in TWC.
Highlights
Unburnt hydrocarbons (UHC), carbon monoxide (CO), and nitrogen oxides (NOx) are the major noxious gases present in the exhaust of internal combustion engines
Perovskite-type oxides are reviewed in relation to their application in exhaust after-treatment technologies as three-way catalysts (TWC)
The possibility to accommodate simultaneously different metal cations at A- and B-sites allows to tune the catalytic properties for a specific application such as Three-Way Catalytic (TWC), which requires redox properties with high thermal stability
Summary
Unburnt hydrocarbons (UHC), carbon monoxide (CO), and nitrogen oxides (NOx) are the major noxious gases present in the exhaust of internal combustion engines. In order to comply with the stringent emission levels imposed by the legislation, these compounds have to be eliminated before they are released into the surrounding environment For this purpose, gasoline-powered vehicles are equipped with a Three-Way Catalytic (TWC) converter. Natural gas vehicles (NGV) generate exhaust emissions containing higher concentrations of methane, a potent greenhouse gas [3] and the most difficult hydrocarbon to oxidize, with respect to their gasoline counterparts For this reason, TWC for NGV are mainly based on Pd, the most active catalyst for methane oxidation, and contain a threefold higher noble metal loading Because of our interest in catalytic converters for NGV applications, the main part of the review is dedicated to the practical aspects of the use of structured perovskite-type oxide catalysts with a special emphasis on TWC. The advantages and limits will be discussed with the aim of identifying the most suitable types of catalysts for automotive applications
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