Advances in fuel chemistries and engine designs over the past few decades have helped vehicles operate more cleanly and efficiently, and treating engine exhaust using a catalytic converter is required in the U.S., Europe, and all over the world to meet ever-tightening environmental regulations.  Additional advances are possible with diesel and lean burning engines, however, emissions from the associated vehicles contain significant amounts of nitrogen oxides. The treatment of these nitrogen oxides – which are toxic and responsible for photochemical smog – is a particular challenge due to the presence of excess oxygen in the exhaust.  A key reaction is the oxidation of nitric oxide (NO) with oxygen to form nitrogen dioxide (NO₂), which usually requires a catalyst containing significant amounts of platinum.

Recently researchers at General Motors discovered that some perovskites are highly active for the oxidation of NO. Perovskite contain relatively inexpensive metals such as La, Mn, and Co, and have the potential to serve as much less expensive alternates to platinum-based catalysts.  While there are reports of the oxidation activities of perovskites, our fundamental understanding of these materials is relatively poor.  To help establish the feasibility of using these catalysts, our team synthesized a series of perovskites, evaluated their performance as NO oxidation catalysts, and characterized key physical and surface chemical properties.  The surface properties of these same structures were simulated using density functional theory methods and correlated with the experimental results.  It was observed that the La-based perovskites with Co or Ni were particularly active materials, and both experimental and simulated results indicated a periodic trend of increased activity as the transition metal increased in atomic number.  Additionally, the substitution of some of the La in the catalyst with Sr significantly improved activity for the cobalt-based perovskites but had little effect on the other types of perovskites. These results will assist in the design of perovskites for NO oxidation.

The project enabled a team consisting of several students, post-doctoral scholars and faculty at the University of Michigan and University of Notre Dame to collaborate with researchers at General Motors and advance our understanding of the surface and catalytic properties of perovskites.  The results have been disseminated to the catalysis and broader communities via several publications and presentations.

Last Modified: 10/04/2014
Modified by: Levi T Thompson