The Mechanism And The Application Of Alkali Metal Catalyst For Soot Combustion

The soot particulate,especially PM2.5,emitted from diesel vehicles have led to the severe gray haze over large area of China in recent years.Due to the small particle size,PM2.5 is easily in breathed into the respiratory tract of human,resulting in respiratory and cardiovascular diseases.In the methods to control the emission of soot particulate,catalytic combustion is the most economical and most effective one.For soot combustion,alkali metals containing materials behave excellent activities.However,the explanation for the catalytic roles of alkali metals are still in dispute,and alkali metals haven’t been applied widely.In this project,the nature of catalysis for alkali metal catalyzing soot combustion will be revealed based on the electronic properties of alkali metals.The study will be begun from the research on the reaction mechanism.The alkali metals（Na,K,Rb and Cs）will be tested to catalyze the reaction of soot with O₂,in which both apparent and inherent activities of alkali metals will be obtained.Furthermore,the unique electronic properties of alkali metals will be related to the data of structure and activities of catalysts.Finally,the nature of catalytic roles of alkali metal will be revealed based on the calculation of electronic structure.Potassium-modified FeCrAl alloy wire mesh was developed as a catalytic diesel particulate filter（CDPF）to suppress the emission of soot from diesel engine.K species were deposited on wire mesh via a chemical vapor deposition method,in which a model soot was used to convert KOH into metallic K at high temperatures（≥ 800 °C）to subsequently activate the wire mesh.The XRF and SEM tests showed that the metallic K reacted with the enriched Al2O3 component on the surface that was derived from the segregation and successive oxidation during the pre-calcination at 950 °C.The resulted layer of K-O-Al species was proved to offer a remarkable activity and stability for catalytic oxidation of diesel soot.The cyclic activity evaluation demonstrated that the K-activated wire mesh can lower the initial temperature of soot combustion to ca.350 °C and keep the activity after five cycles.