Insight into phase structure-dependent soot oxidation activity of K/MnO2 catalyst

In the present study, two nanosized MnO 2 with 0 and 8 phase structures and potassium loaded MnO 2 catalysts with varied K loading amounts (denoted as K/MnO 2 ) were prepared. Temperature programmed oxidation and isothermal reactions in loose contact modes were employed to examine the soot oxidation activity of the as-prepared catalysts. Characterization results show that as compared with 0-MnO 2 , 8-MnO 2 has larger surface area and higher content of hydroxyl groups. Upon K loading, abundant hydroxyl groups in 8-MnO 2 effectively sequestrate K cation to form bound K species and free K species are available only at K loading above 3.0 wt.%. In contrast, the majority of K species present as free state in 0-MnO 2 even at a K loading of 1.0 wt.% due to its very low hydroxyl group content. The O 2 temperature-programmed desorption (O 2 -TPD) demonstrates that the catalysts with free K species exhibit strong ability in activating gaseous O 2 , whereas the catalysts only having bound K display minor O 2 activation capability. As a result, despite of slightly lower activity of 0-MnO 2 than 8-MnO 2 , the K/ 0-MnO 2 catalysts exhibit substantially higher activities than K/ 8-MnO 2 catalysts with identical K loadings. The finding in this study clearly demonstrates that for MnO 2 based catalysts, the enhancement of catalytic activity for soot oxidation is highly K loading amount dependent and the dependency is strongly associated with the phase structure of MnO 2 . ?? 2022 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.