Transition Metal Hydride Catalysts for Sustainable Interconversion of CO2 and Formate: Thermodynamic and Mechanistic Considerations

Kate M. Waldie, Felix M. Brunner, Clifford P. Kubiak

Research output: Contribution to journalArticlepeer-review

47 Scopus citations

Abstract

Hydride transfer between transition metal hydride complexes and carbon dioxide is a known reaction, where the thermodynamically favored direction of hydride transfer determines whether CO2 reduction or formate oxidation occurs. Analysis of a growing database of thermodynamic parameters for transition metal hydride complexes now provides clear demarcation between metal hydrides which will function as oxidases and as reductases. The turning point is set at the hydricity of formate (44 kcal/mol in acetonitrile). Here, we utilize hydricity as a framework to reevaluate the catalytic activity and proposed mechanisms for formate oxidation and CO2 reduction with several Ni and Rh P2N2 (P2N2 = 1,5-diaza-3,7-diphosphacyclooctane) complexes, respectively. The series of Ni P2N2 complexes have hydricities between 55-64 kcal/mol and are active catalysts for the electrochemical oxidation of formate. A surprising correlation of increased rate of electrochemical oxidation with decreased overpotential, ν, is observed. The Rh P2N2 complexes have hydricities between 28-34 kcal/mol and function as hydrogenation catalysts for the reduction of CO2 to formate. Learning from the reactivity of these catalysts, design principles for future metal hydride complexes are presented that focus on the ultimate goal of catalyst optimization for improved energy efficiency (overpotential) with high selectivity (Faradaic efficiency) for both formate oxidation and CO2 reduction to formate.

Original languageEnglish (US)
Pages (from-to)6841-6848
Number of pages8
JournalACS Sustainable Chemistry and Engineering
Volume6
Issue number5
DOIs
StatePublished - May 7 2018
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • Environmental Chemistry
  • General Chemical Engineering
  • Renewable Energy, Sustainability and the Environment

Keywords

  • Carbon dioxide
  • Formic acid
  • Hydricity
  • Molecular catalysis
  • Nickel
  • Phosphine ligands
  • Rhodium

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