Understanding the Relationship Between Kinetics and Thermodynamics in CO 2 Hydrogenation Catalysis
- Catalysis Science Group, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
Linear free-energy relationships have been identified that link the kinetic activity for catalytic hydrogenation of CO2 to formate with the thermodynamic driving force for the rate-limiting steps of catalysis. Cobalt and rhodium bis(diphosphine) complexes with different hydricities (G°H-), acidities (pKa), and free energies for H2 addition (G°H2) were examined. Catalytic CO2 hydrogenation was studied under 1.8 and 20 atm of pressure (1:1 CO2:H2) at room temperature in tetrahydrofuran with a spread of turnover frequencies (TOF) ranging from 0 to 74,000 h-1. The catalysis was followed by 1H and 31P NMR in real time under all conditions to yield information about the rate determining step. Catalysts exhibiting the highest activities were found to have hydride transfer and hydrogen addition steps that were each downhill by approximately 6 to 7 kcal/mol, and the deprotonation step was thermoneutral. The research by M.S.J., A.M.A., E.S.W., and J.C.L. was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. The research by E.B.H., M.L.H., and M.T.M. (X-ray crystallography, synthesis) was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. The authors thank Dr. Samantha A. Burgess for assistance in collecting cyclic voltammetry data. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US); Energy Frontier Research Centers (EFRC) (United States). Center for Molecular Electrocatalysis (CME)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1406706
- Report Number(s):
- PNNL-SA-125045; KC0302010
- Journal Information:
- ACS Catalysis, Journal Name: ACS Catalysis Journal Issue: 9 Vol. 7; ISSN 2155-5435
- Publisher:
- American Chemical Society (ACS)
- Country of Publication:
- United States
- Language:
- English
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