Toyota Central R&D exploring controlling catalysts at the quantum level for optimized performance and reduced costs
The Frontier Research Center (FRC) at Toyota Central R&D Labs in Japan is investigating the development of catalysts controlled at the quantum level. This level of control should result in an an extreme reduction of precious metal usage in automotive exhaust catalysts and/or fuel cells, said Dr. Yoshihide Watanabe, program manager of the Quantum Controlled Catalysis Program at the FRC.
Metal cluster chemistry (a cluster is a group of atoms or molecules formed by interactions varying in strength from very weak to strong) has been developing rapidly since the mid-20th century. Some naturally occurring clusters are known to be involved in catalytic reactions, and there is great interest in the potential use of synthetic clusters in industrial applications such as catalysis.
In a recent open access paper published in the journal Science and Technology of Advanced Materials, Dr. Watanabe reviewed studies on different types of reactions involving metal clusters deposited on a support material in light of the relationship between atomically controlled cluster sizes and catalytic activity. The reactions reviewed include CO oxidation; NO–CO reactions; acetylene cyclotrimerization; hydrazine decomposition; cyclohexene aerobic oxidation; photocatalytic reactions; and electrochemical reactions (oxygen reduction reactions and oxygen evolution reactions).
He observed that not much research has been done in the area of atomically controlled cluster catalysis, with the exception of studies on the CO oxidation reaction important to catalytic converters in automobiles.
His research indicates that catalytic activity is strongly affected by the electronic structure of clusters, their geometry on a support material, and the interaction between the cluster and the material. Thus, the catalytic activity of clusters can be enhanced by controlling cluster size and the interaction between the clusters and the support material.
There are two main motivating forces in the field of atomically controlled cluster catalysis. One is to study the mechanism of catalysis and the other is to explore size-specific catalytic activity. Studies employing atomically precise clusters as well-defined model catalysts are continuously conducted with the goal of understanding the true nature of catalysis. With an atomically precise, controlled catalyst, it is reasonable to use these as model catalysts. Because we still have only patchy information, and many difficulties remain, it is necessary to continue making persistent efforts.
A few studies have focused on quantum effects on the catalytic properties of size-controlled clusters. Although several mechanisms have been suggested, these effects remain poorly understood. It has been proposed that in the studies reviewed in this paper that it is possible to tune the electronic structure through atomic control of the cluster size. In addition to so-called HOMO–LUMO energy gap [earlier post], the hybridization between the electronic states of the adsorbed reactant molecules and cluster at EF can be tuned to realize a quantum-controlled catalyst.—Watanabe 2014
Enhancing the catalytic activity of some clusters could greatly reduce the utilization of precious metals as catalytic agents. A few studies that try to understand how the catalytic properties of size-controlled clusters are affected at the quantum level. Although several mechanisms for these effects are suggested, the field is still in progress, he said.
There is one last point that is eagerly anticipated. Computational chemistry will move into the frontline and lead the way to the growth and development of atomically precise cluster catalysis towards quantum-controlled catalysts. Sophisticated software and hardware for computational chemistry and an accessible database specifically developed for the cluster research will be useful. Exchange of useful knowledge among experimental and computational scientists, particularly those working on cluster and surface chemistry, is also important. Finally, this field of research should be sup- ported industry and governments across borders. In closing, it would be great help if the killer application for atomically precise cluster catalysis will be developed soon.—Watanabe 2014
Yoshihide Watanabe (2014) “Atomically precise cluster catalysis towards quantum controlled catalysts.” Science and Technology of Advanced Materials 15 (6): 063501 doi: 10.1088/1468-6996/15/6/063501