Oxide coatings modified with transition and rare-earth metals on aluminum and their activity in CO oxidation

Abstract

Oxide catalysts, which, in addition to Al₂O₃ + SiO₂, contain from one (Ni) to four oxides or compounds of transition metals (Ni, Cu, Mn, and Co) and oxides or compounds of rare-earth elements (Ce, La), are produced on D16 aluminum alloy by plasma electrolytic oxidation combined with impregnation and subsequent annealing. The composites formed begin to catalyze the CO oxidation in a temperature range of from 100 to 300°C. The catalysts used can be arranged in the following series of decreasing catalytic activity: Ni-Cu-Mn-Co-Ce > Ni-Cu-Mn-Co-Ce-La ≈ Ni-Cu-Mn-Co > Ni-Cu-Mn > Ni-Cu > Ni. Oxygen compounds of Cu⁺, Cu²⁺, Mn⁴⁺, Co³⁺, Ce³⁺, and Ce⁴⁺, which seem to determine the catalytic properties of the oxide systems studied, are found on the surface and in the subsurface layer with a total thickness of ∼6 nm of the most active Ni-Cu-Mn-Co-Ce catalyst.