Effect of surface manganese oxide species on soot catalytic combustion of Ce–Mn–O catalyst

Abstract

Constructing cerium and manganese bimetallic catalysts with excellent catalytic performance for soot combustion is the research frontier at present. In order to find out the key factors for catalytic soot combustion of Ce–Mn–O catalysts, a series of Ce–Mn–O catalysts with different Ce/Mn proportions were prepared by co-precipitation method. The activity test results show that it increases first and then decreases with the increase of Mn content. The best catalytic activity is obtained for Ce0.64Mn0.36 catalyst, which shows a maximum rate temperature (Tm) at 306 °C for CO2 production in TPO curve. Compared with non-catalytic soot combustion, the Tm decreases by more than 270 °C. Systematical characterization results suggest that when the adsorbed surface oxygen, lattice oxygen, specific surface area and total reduction amount of the catalysts reach a certain value, the key factors leading to the difference of catalytic activity become the readily reducible and highly dispersed surface manganese oxide species and contact performance of the external surface. The surface manganese oxide species is beneficial to improving the low-temperature reducibility of catalysts and the porous surface is conducive to the contact between catalyst and soot. Furthermore, for the soot combustion reaction containing only O2, the promoting effect of Mn4+ is not obvious.