Goal
Replace expensive precious-metal catalysts in automotive exhaust after-treatment with low-cost perovskite materials while maintaining or improving NOx conversion performance.
Problem
High cost and limited supply of platinum-group metals (PGM) in diesel oxidation (DOC) and lean NOx trap (LNT) catalysts, and their poor thermal durability.
Concept Summary
Strontium-doped perovskite oxides (e.g., La_1_-_xSr_xCoO_3 and La_1_-_xSr_xMnO_3) are used as catalytic active phases on monolith substrates to oxidize NO to NO_2 and reduce NOx, offering comparable or superior performance to commercial platinum-based catalysts at a fraction of the cost.
Detailed Description
GM researchers synthesized perovskite oxides doped with strontium and coated them onto honey-comb ceramic monoliths. In simulated diesel exhaust, La_1_-_xSr_xCoO_3 achieved higher NO-to-NO_2 conversion than a commercial Pt DOC catalyst, while La_0._9Sr_0._1MnO_3 LNT matched Pt-based NOx reduction. The catalysts are thermally stable, mechanically robust, and can be further improved by adding palladium to mitigate sulfur poisoning.
Principles
- Catalytic oxidation of NO to NO_2
- Lean NOx trap adsorption/reduction
- Perovskite crystal-structure activity
- Substitution of PGM with transition-metal oxides
Scientific Domains
Materials
- Lanthanum (La)
- Strontium (Sr)
- Cobalt (Co)
- Manganese (Mn)
- Gamma-Al_2O_3
- CemZr_1_-_mO_2
- LaMnAl_1_1O_1_9
- BaMnAl_1_1O_1_9
- Sr_1_2Al_1_4O_2_1
Mechanisms of Action
- NO oxidation on perovskite surface
- NOx adsorption on LNT storage sites
- Redox cycling of Co/Mn oxidation states
- Thermal stability due to perovskite lattice
Energy Sources
Applications
- Automotive diesel after-treatment
- Lean-burn gasoline engine emissions control
- Industrial NOx reduction
Claimed Performance
Higher NO-to-NO_2 conversion than commercial Pt DOC catalyst; NOx reduction comparable to Pt-based LNT under realistic exhaust conditions.
Experimental Evidence
Lab-scale tests in simulated diesel exhaust showed La_1_-_xSr_xCoO_3 outperformed Pt DOC in NO oxidation; La_0._9Sr_0._1MnO_3 LNT achieved NOx reduction similar to Pt LNT. Graphs of conversion vs. temperature were presented in the Science article and associated press releases.
Replication Status
Results reported by GM and published in Science; no independent replication documented in the article.
Limitations
- Catalyst deactivation by sulfur in fuel
- Performance may depend on palladium addition
- Scale-up manufacturing not yet demonstrated
