Understanding the Relationship between Kinetics and Thermodynamics in CO2 Hydrogenation Catalysis

Matthew S. Jeletic, Elliott B. Hulley, Monte Helm, Michael T. Mock, Aaron Appel, Eric Wiedner, John Linehan

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

Catalysts that are able to reduce carbon dioxide under mild conditions are highly sought after for storage of renewable energy in the form of a chemical fuel. This study describes a systematic kinetic and thermodynamic study of a series of cobalt and rhodium bis(diphosphine) complexes that are capable of hydrogenating carbon dioxide to formate under ambient temperature and pressure. Catalytic CO2 hydrogenation was studied under 1.8 and 20 atm of pressure (1:1 CO2/H2) at room temperature in tetrahydrofuran with turnover frequencies (TOF) ranging from 20 to 74000 h-1. The catalysis was followed by 1H and 31P NMR spectroscopy in real time under all conditions to yield information about the rate-determining step. The cobalt catalysts displayed a rate-determining step of hydride transfer to CO2, while the hydrogen addition and/or deprotonation steps were rate limiting for the rhodium catalysts. Thermodynamic analysis of the complexes provided information on the driving force for each step of catalysis in terms of the catalyst hydricity (G°H), acidity (pKa), and free energy for H2 addition (G°H 2). Linear free-energy relationships were 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. The catalyst exhibiting the highest activity, Co(dmpe)2H, was found to have hydride transfer and hydrogen addition steps that were each downhill by approximately 6 to 7 kcal mol-1, and the deprotonation step was thermoneutral. This indicates the fastest catalysts are the ones that most efficiently balance the free energy relationships of every step in the catalytic cycle.

Original languageEnglish
Pages (from-to)6008-6017
Number of pages10
JournalACS Catalysis
Volume7
Issue number9
DOIs
Publication statusPublished - Sep 1 2017

Fingerprint

Catalysis
Hydrogenation
formic acid
Thermodynamics
Catalysts
Kinetics
Free energy
Rhodium
Deprotonation
Cobalt
Carbon Dioxide
Hydrides
Hydrogen
Carbon dioxide
Acidity
Nuclear magnetic resonance spectroscopy
Catalyst activity
Temperature

Keywords

  • carbon dioxide
  • cobalt
  • homogeneous catalysis
  • hydricity
  • hydrogenation
  • rhodium

ASJC Scopus subject areas

  • Catalysis

Cite this

Understanding the Relationship between Kinetics and Thermodynamics in CO2 Hydrogenation Catalysis. / Jeletic, Matthew S.; Hulley, Elliott B.; Helm, Monte; Mock, Michael T.; Appel, Aaron; Wiedner, Eric; Linehan, John.

In: ACS Catalysis, Vol. 7, No. 9, 01.09.2017, p. 6008-6017.

Research output: Contribution to journalArticle

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