Structural properties of alumina supported Ce–Mn solid solutions and their markedly enhanced catalytic activity for CO oxidation

Abstract

This work presents the synthesis and characterization of alumina supported ceria–manganese solid solutions (Ce–Mn/Al), which were prepared by a deposition coprecipitation method followed by calcination at different temperatures from 773 to 1073K. The physicochemical properties of the synthesized samples were deeply investigated by various characterization techniques, namely, XRD, ICP-OES, BET surface area, TEM-HRTEM, Raman, XPS, and H2-TPR. The catalytic activity was evaluated for CO oxidation. BET surface area measurements revealed that synthesized samples exhibit reasonably high specific surface area. XRD and Raman results confirmed that the present Ce–Mn/Al samples are single-phase solid solutions with good structural homogeneity and high thermal stability up to 1073K. TEM analyses showed that the particle sizes of Ce–Mn/Al samples are in the range of ∼5–14nm. XPS analysis revealed that Ce is in the form of Ce4+ and Ce3+, and Mn existed in the form of Mn4+, Mn3+, and Mn2+ on the surface of the samples. The solid solution particles in the nanosize form are well distributed over the support surface. As a result of solid solution formation and high dispersion over the support, the Ce–Mn/Al samples exhibited better redox behaviour. The CO oxidation results revealed that the Ce–Mn/Al samples show an excellent CO oxidation performance compared with alumina supported undoped CeO2 (Ce/Al) and MnOx (Mn/Al) samples. Among various samples, the Ce–Mn/Al calcined at 773K showed outstanding CO activity with T50=∼340K. The enhanced catalytic activity was mainly attributed to high surface area, large amount of oxygen vacancies, and excellent redox behaviour. The metal–support interaction also seems to play a decisive role in their high catalytic activity by stabilizing the Ce–Mn–O dispersion.