Preliminary performance studies of Al–Co–Mn mixed oxide and Ag-doping for the purpose of PGM-free DOC

Abstract

Lean-burn engine powered vehicles are increasing through the world for better fuel combustion efficiencies. Diesel engines, taking lean-burn policy, essentially use platinum (Pt) as a catalyst for an after-treatment of their exhaust, called diesel oxidation catalyst (DOC). It is a great issue to reduce the use of platinum group metals (PGM) with respect to costly aspect. We are here reporting a preliminary oxidation performance results of a PGM-free mixed oxide of powdered Al1.8Co4.4MnO9.6+x with nonstoichiometric oxygen composition through a temperature ramp-up transient analysis. The mixed oxide was found having spinel structured mixed phase of Co3O4, Co2AlO4, and CoMn2O4 with excess oxygen weakly bonded to the transition metals at high oxidation states. The bare Al1.8Co4.4MnO9.6+x showed excellent activities for CO oxidation, which was greatly faster than 1.3%-Pt doped alumina, and HC oxidation was shown slightly slower than CO oxidation. Through the impregnation effect tests of precious metals such as Ag, Pd and Pt on the mixed oxide, 3% Ag-doped Al1.8Co4.4MnO9.6+x was found showing the highest oxidation activity for CO and HC oxidation. The results are providing a possibility to substitute for Pt-based DOC with a low cost PGM-free catalyst.