Aftertreatment PGM Catalysts with Atomic Precision for Optimal Reaction Efficiency

Ming  Yang, General Motors, Global Research and Development Center

Ming Yang,Se Oh, Wei Li

Chemical and Materials Systems Laboratory, General Motors Research and Development, Warren, MI 48092

For the expensive and heavily used platinum-group metal (PGM) catalysts, how we identify and build the catalytic sites with a uniform atomic precision, so that they remain stable and active under severe reaction condition, is critical to the automotive industry. Herein, we discuss a few of our designs of emission purification catalysts that aim to maximize intrinsic catalytic activity and to retain hydrothermal stability of the platinum species supported on either ceria or alumina substrates.

An ideal supported metal catalyst must simultaneously make the most of the full metal dispersion and the optimal intrinsic activity per metal atom. As the workhorse in vehicle aftertreatment catalysts, the alumina-supported PGM catalysts’ performance deteriorates after extensive ageing, largely due to the loss of PGM dispersion.On a widely used La-stabilized alumina support, we found that the elusive and atomically dispersed platinum is the true relevant catalytic species in oxidizing CO and C₃H₆. As a natural next step, a Ba-stabilized PGM catalyst was developed that contains fully dispersed Pt₁-O_x– on alumina support, showing promising resistance to PGM sintering in the meantime. Regarding the catalysts having atomically dispersed Pt on ceria, however, it remained a daunting task to unlock the high intrinsic activity per Pt atom, despite of the encouraging 100 % Pt dispersion. A mild treatment, which is to potentially reflect the fuel-rich engine operation albeit a much cleaner environment, was developed by us to activate various single-atom Pt/CeO₂catalysts. The new catalytic center is, instead, the ~1 nm Pt_nO_xcluster retaining full dispersion but being about 20 times more activewith or without co-feeding water in the reaction. The knowledge sees expansion when using various ceria supports and applying hydrothermal ageing treatment at elevated temperatures.

Our findings may provide new insights into the development of next-generation PGM-support catalysts, which hold the promise to tackle future low-temperature aftertreatment challenges.