Catalytic Soot Combustion─General Concepts and Alkali Promotion

Abstract

In this Review, we discuss catalytic systems for soot combustion. The focus is on alkali-containing materials since they exhibit the most promising and platinum group metal (PGM) free solutions, providing highly efficient catalysts at a low price. The wide range of experimental conditions used for catalyst evaluation and parameters commonly used to compare different materials was scrutinized. The presented synthetic summary of the classical and long-researched materials reveals that the most active catalysts, which may fulfill the low-temperature activity apart from PGM-based systems, are only those containing alkalis as beneficial dopants. The alkali promotion by surface doping or nanostructuration of earth abundant transition metal oxides emerged as an effective way to develop effective soot oxidation catalytic materials; therefore, the physical nature of alkali promotion is thoroughly discussed. A detailed presentation of the state of the art three-dimensional macroporous materials is presented, as these catalysts combine beneficial catalytic activity with morphological features designed for enhancing the contact between the catalyst and the soot particles. Finally, a set of reactivity descriptors for the alkali-promoted catalysts (work function, alkali desorption energy, and oxygen availability) was proposed to foster the rational design of catalytic materials for soot oxidation.

Highly Efficient Catalytic Soot Combustion Over Potassium‐Promoted Pine Needles‐Like CoMnO Nanoarray Monolithic Catalysts

“…After introducing NO to the reaction atmosphere, the active oxygen species primarily oxidize NO to form NO 2 , and then potassium can adsorb and storage NO 2 to form chemisorbed NO 2 species at lower temperatures (< 340 °C). [31,57] When the temperature is less than 340 °C, the soot particulates can only be oxidized by the chemisorbed NO 2 species and gaseous NO 2 to CO 2 , by this time, the surface adsorbed oxygen species is inactive and cannot oxidize the soot particulates. In this process of catalytic oxidation, the soot combustion process begins with the increase of the NO 2 signal, as evidenced by the results of Soot-TPO and NO-TPO.…”

Review of Shape-Controlled CeO2 Nanocatalysts for Purification of Auto-Exhaust Pollutants

“…As estimated by the World Health Organization, air pollution is causing ∼7% of the world’s deaths each year. The automotive industry accounts for the release of a major portion of toxic air pollutants, such as carbon monoxide (CO), soot particulates, and nitrogen oxides (NO x ). − Volatile organic compounds (VOCs), released from various stationary chemical industries and indoor sources, are also identified as toxic air pollutants because of their carcinogenic nature. − Thus, the purification of these air pollutants at ambient conditions is of utmost importance for a sustainable ecosystem.…”

Highly Reactive Peroxide Species Promoted Soot Oxidation over an Ordered Macroporous Ce0.8Zr0.2O2 Integrated Catalyzed Diesel Particulate Filter

“…The efficiency of soot oxidation is greatly influenced by the contact area between the catalyst and soot particles. 14 Powdertype catalysts, when coated on DPF with a low surface area, demonstrated suboptimal catalytic performance due to their low soot−catalyst contact efficiency. 15−17 Therefore, the enhancement of soot−catalyst contact should be considered in the development of high-efficiency soot combustion catalysts.…”

“…The efficiency of soot oxidation is greatly influenced by the contact area between the catalyst and soot particles . Powder-type catalysts, when coated on DPF with a low surface area, demonstrated suboptimal catalytic performance due to their low soot–catalyst contact efficiency. − Therefore, the enhancement of soot–catalyst contact should be considered in the development of high-efficiency soot combustion catalysts. , Three-dimensionally ordered macroporous (3DOM) materials, characterized by their increased surface area and abundant pore structure, have been demonstrated to enhance the contact efficiency between the soot and catalyst.…”