For multiple aspects of the present-day society, it is vital to find the optimal binding energies for heterogeneous chemical reactions, in which the reactant is a gas or liquid and the catalyst is a solid, since processes as different as the production of plastics and fertilizers are dependent on such chemical reactions.
There occurs an optimal binding energy—the extent to which the reactants interact with the catalyst—at which the processes occur most efficiently. If this energy is very low, the reactants do not react with the catalyst, and if this is very high, they will remain attached to the catalyst. Hence, catalysts are developed based on this.
Currently, as part of a study, the results of which could enable the development of new catalysts that do not rely on high-cost rare metals, researchers from the RIKEN Center for Sustainable Resource Science have demonstrated that the optimal binding energy can deviate from conventional calculations, which are dependent on equilibrium thermodynamics, at higher rates of reaction.
This implies that the development of catalysts has to be redesigned again using the new calculations to achieve the best rates.
Various industrial methods involve heterogeneous chemical reactions. Some of the well-known reactions are as follows: the production of plastics using the Ziegler-Natta reaction, the production of ammonia through the Haber-Bosch process, and the desulfurization of petroleum. Based on experiments, in 1911, Paul Sabatier, a French chemist, hypothesized that an optimal binding energy promotes higher catalytic activity.
Recently, developments in computational chemistry have offered a framework that can be used to determine the optimal binding energy, based on equilibrium thermodynamics and on the assumption that the process will advance smoothly given all steps in the process are thermodynamically favorable. In this process, the catalyst has to improve the thermodynamics of the most unfavorable step.
The catch is that “optimum” is often understood to imply that the reaction needs as smaller a driving force as possible, such that it can be thermodynamically efficient. However, in the real world, it is generally more practical to have a higher catalysis rate, even if a larger driving force is needed.
On the basis of reaction kinetic modeling, which considers this discrepancy, the researchers carried out a new set of calculations and determined new optimal binding energies for hydrogen oxidation conducted by heterogeneous catalysis. They found that the calculations gave different values at high reaction rates.
We were happy to see that our calculations predict new strategies of catalyst design which could not have been obtained using the traditional, thermodynamic approach.
Hideshi Ooka, Study First Author, RIKEN Center for Sustainable Resource Science
Ryuhei Nakamura, head of the Center for Sustainable Resource Science’s Biofunctional Catalyst Research Team, said, “Based on this finding, we plan to look for new catalysts, using elements such as copper or nickel, that can push heterogeneous catalytic reactions forward but are less costly and more environmentally friendly than the current ones, which often require precious metals such as platinum and palladium.”
Consequently, research to find new catalysts using our method could contribute to reaching three of the United Nations Sustainable Development Goals: Goal 7 (affordable and clean energy), Goal 12 (responsible production and consumption), and Goal 13 (climate action).
Ryuhei Nakamura, Head, Biofunctional Catalyst Research Team, RIKEN Center for Sustainable Resource Science