Cerium mischmetal role in the catalytic washcoat properties

Cerium mischmetal or rare earth mischmetal in the form of unseparated rare earth elements is an alloy of approximately 55% cerium (Ce), 25% lanthanum (La), 15-18% neodymium (Nd) with smaller amounts of others following. As a catalytic material, these metals act as active catalysts, supports, and dopants [1,2]. The change of oxidation state between +4 and +3 is the significant for the catalytic activity of the ceria based materials. Oxygen transport in ceria follows the vacancy mechanism so that by oxygen vacancy creation, the system needs to supply oxygen. The oxygen lost at the surface is compensated by the movement of oxygen from the bulk regions. Fig 1. shows the mechanism of soot oxidation over an Ag@CeO2 catalyst [3]. Lanthanum is commonly used as a dopant to stabilize the gamma phase of alumina in catalysts used in high temperature conditions, such as in automotive three-way catalytic converter. Lanthanum also improves catalysts for applications at low temperature such as nickel and copper-based solids for carbon monoxide oxidation [4]. In this study, the performance and durability of catalytic converter washcoat were investigated in the presence of cerium-lanthanum oxide mixture. In the presence of these metal oxides, the amount of platinum group metals (PGM) consumed decreases dramatically. In this study the ultrasonic assistant solvothermal method was used. Nano structured washcoats containing alumina-based cerium-lanthanum oxides in the presence of zirconia have been synthesis. We used ethanol as solvent and acetylacetone as complexing agent. FESEM image of the synthesized sample is shown in Fig. 2.

Keywords:

Cerium , mischmetal , waschcoat , catalyst