Plasma-assisted deposition of Mn and Fe phases on CeO biomorphic fibers for soot combustion and CO oxidation

Abstract

In the present work, the gliding arc (glidarc) plasma technique is for the first time explored as a novel precipitation-deposition method to generate fibrous catalysts. Precisely, Mn and Fe oxides were plasma-precipitated on a fibrous ceria support and evaluated in two reactions of environmental interest, (1) soot combustion and (2) CO oxidation. Pure CeO2 fibers (Fib Ce) were obtained via a biotemplate route with the idea of starting from a support already active in oxidation reactions, and then further improving its activity by supporting on its surface Fe and Mn oxides. The precipitates were identified by XRD, FTIR and LRS, and their loadings and distributions assessed by ICP and EDX respectively. α-Fe2O3 and Mn3O4 phases were detected. XPS confirmed the presence of Mn and Fe on the surface of Fib Ce and revealed that the deposition of Fe logically gave a superficial Fe/Ce ratio much higher than the bulk one and provoked an increase in Ce3+/Ce4+ and Oads/Ce ratios. On the contrary, Mn-supported samples did not affect considerably the Ce3+/Ce4+ and Oads/Ce ratios and presented a Mn/Ce ratio closer to that of the bulk. The latter suggests that Mn has integrated the ceria structure. For reaction (1), the deposition of Fe by plasma drastically degraded the performance of the bare support, whereas Mn deposition greatly increased the activity of Fib Ce. The same activity order was observed for reaction (2): Mn-Fib Ce > Fib Ce > Fe-Fib Ce.