Performance Of K₂Ti₈O₁₇ Supported Mn,Co Metal Oxide Catalysts For Soot Catalytic Combustion

The soot emitted from the exhaust of diesel engines is very detrimental to environment and human health as the popularity of diesel engines increases.Now the technique applied in a large scale is filter traps,the core of which is an effective soot catalyst.K-containing catalyst becomes a research focus due to their lower cost and better activity,but it losses activity by sublimation at a higher temperature.In this work,K₂Ti₈O₁₇7 is chosen as a candidate because it makes a good balance of activity and stability,based on which series of K₂Ti₈O₁₇7 catalyst loaded with Mn,Co metal oxides is designed.A series of Mn-based soot catalysts supported on K₂Ti₈O₁₇7 nanobelt xMn/K₂Ti₈O₁₇?x=0%,5%,10%,15%,mass fraction?was successfully synthesized and showed excellent performance in catalytic soot combustion.It was found that10%Mn/K₂Ti₈O₁₇7 exhibited the highest activity,which is attributed to the activity of the support K₂Ti₈O₁₇7 itself and the well-distributed particle of MnO_x,a benefit to the contact of the catalysts and soot.Based on the result of H₂-TPR,XPS,soot-TPR,the excellent catalytic performance of 10%Mn/K₂Ti₈O₁₇7 is attributed to the well-distributed MnO_x particles,which has strong interaction with the support,leading to the abundance of Mn⁴⁺.Mn⁴⁺plays a key role in redox cycles,thus the best redox property of the catalyst is obtained.Another factor contributing to the activity of 10%Mn/K₂Ti₈O₁₇7 is the profusion of surface absorbed oxygen as active oxygen,as well as the improved mobility of oxygen species.With good mobility of oxygen species,the consumption of absorbed oxygen in combustion process could be supplemented by the transfer of lattice oxygen,resulting in an accelerated reaction speed.Other factors contributing to the soot catalytic combustion on 10%Mn/K₂Ti₈O₁₇are also examined.In the temperature programmed oxidation system which is used to simulate practical condition,it was found that the rate of flow,mode of contact,and the composition of reactive gas all had an impact on soot catalytic performance.The lower rate of flow?50 mL?prolonged the retention time of reactive gas on the mixture of soot and catalyst,making sufficient contact of the gas and solid.The mode of tight contact provides the larger area of contact between the soot and catalyst,and in this way the active sites on the surface of catalysts are used more effectively.The presence of NO in reactive gas is crucial in soot combustion by forming NO₂ with O₂,which is more oxidative than O₂.NO₂ involves in the soot combustion,altering reaction route and accelerating the rate of reaction.Another study in this work is the synthesis of a series of Co-based soot catalysts supported on K₂Ti₈O₁₇7 nanobelt x Mn/K₂Ti₈O₁₇?x=0%,5%,10%,15%,mass fraction?.The activity test showed that the more loadings of coblat caused the higher activity,with the highest activity at the loading of 15%.The activity of 5%Co/K₂Ti₈O₁₇7 is lower than 15%Co/K₂Ti₈O₁₇7 due to the lack of active Co species,though it possesses larger specific surface area.25%Co/K₂Ti₈O₁₇7 exhibits no better activity than 15%Co/K₂Ti₈O₁₇,because when the loading of Co further increased,the accumulated cobalt oxide leads to the decreased specific surface area.The result of H₂-TPR and soot-TPR displayed the strongest redox property of 25%Co/K₂Ti₈O₁₇and the largest amount of surface active oxygen,which result in similar activity of the two catalysts.