Mechanistic insights to drive catalytic hydrogenation of formamide intermediates to methanol via deaminative hydrogenation

Amine-promoted hydrogenation of CO2 to methanol typically proceeds via a formamide intermediate when amines are used as additives or if the hydrogenation is performed in carbon capture solvents. The catalysts used for the hydrogenation of the formamide intermediate dictate the selectivity of the products formed: 1) Deoxygenative hydrogenation (C–O bond cleavage) resulting in N-methylation of amine and deactivation of the solvent, 2) Deaminative hydrogenation (C–N bond cleavage) resulting in formation of methanol and regeneration of the solvent. To date, catalytic reductions of CO2 with amine promoters suffer from poor selectively for methanol which we attribute to the limiting formamide intermediate, though to date, the conditions that favor C–N cleavage have yet to be fully understood. To better understand the reactivity of the formamide intermediates, a range of heterogenous catalysts were used to study the hydrogenation of formamide. Well-known gas phase CO2 hydrogenation catalysts catalyze the hydrogenation of formamide to N-methyl product via C–O bond cleavage. However, the selectivity can be readily shifted to selective C–N bond cleavage by addition of an additive with sufficient basicity for both homogenous and heterogeneous catalytic systems. The base additive shifts the selectivity by deprotonating a hemiaminal intermediate formed in situ during the formamide hydrogenation. This prevents dehydration process leading to N-methylated product, which is a key capture solvent deactivation pathway that hinders amine use in carbon capture, utilization, and storage (CCUS). The findings from this study provide a roadmap on how to improve the selectivity of known heterogenous catalysts, enabling catalytic reduction of captured CO2 to methanol

Highlights of the 2021–2022 Award-Winning Research Accomplishments in the ACS Energy and Fuels Division

The Energy and Fuels Division (ENFL) of the American Chemical Society (ACS) aims to promote and advance energy-related research, development, and education to address the world’s energy and chemical challenges. During the Fall 2021 and Spring 2022 National Meetings, a select group of our talented and distinguished ENFL colleagues received ACS divisional and national awards. They participated in a series of symposia held in their honor to recognize their stellar achievements and original contributions in diverse areas, including but not limited to production chemistry, energy conversion and storage, energy utilization, and carbon management. These award recipients carried out multi-disciplinary and cutting-edge research in various academic, industrial, and national laboratory settings to thoughtfully tackle a number of socially impactful but unsolved energy and fuel problems, using innovative science-based solutions and strategies. In this publication, we highlight nine of these remarkable individuals with a focus on their noteworthy, ground-breaking accomplishments

Homogeneous Hydrogenation of CO₂ to Methyl Formate Utilizing Switchable Ionic Liquids

Combined capture of CO₂ and subsequent hydrogenation allows for base/methanol-promoted homogeneous hydrogenation of CO₂ to methyl formate. The CO₂, captured as an amidinium methyl carbonate, reacts with H₂ with no applied pressure of CO₂ in the presence of a catalyst to produce sequentially amidinium formate, then methyl formate. The production of methyl formate releases the base back into the system, thereby reducing one of the flaws of catalytic hydrogenations of CO₂: the notable consumption of one mole of base per mole of formate produced. The reaction proceeds under 20 atm of H₂ with selectivity to formate favored by the presence of excess base and lower temperatures (110 °C), while excess alcohol and higher temperatures (140 °C) favor methyl formate. Known CO₂ hydrogenation catalysts are active in the ionic liquid medium with turnover numbers as high as 5000. It is unclear as to whether the alkyl carbonate or CO₂ is hydrogenated, as we show they are in equilibrium in this system. The availability of both CO₂ and the alkyl carbonate as reactive species may result in new catalyst designs and free energy pathways for CO₂ that may entail different selectivity or kinetic activity

Two coexisting liquid phases in switchable ionic liquids.

Switchable ionic liquids (SWILs) derived from organic bases and alcohols are attractive due to their applications in gas capture, separations, and nanomaterial synthesis. However, their exact solvent structure still remains a mystery. We present the first chemical mapping of a SWIL solvent structure using in situ time-of-flight secondary ion mass spectrometry. In situ chemical mapping discovers two coexisting liquid phases and molecular structures vastly different from conventional ionic liquids. SWIL chemical speciation is found to be more complex than the known stoichiometry. Dimers and ionic clusters have been identified in SIMS spectra; and confirmed to be the chemical species differentiating from non-ionic liquids via spectral principal component analysis. Our unique in situ molecular imaging has advanced the understanding of SWIL chemistry and how this "heterogeneous" liquid structure may impact SWILs' physical and thermodynamic properties and associated applications

Two coexisting liquid phases in switchable ionic liquids.

Switchable ionic liquids (SWILs) derived from organic bases and alcohols are attractive due to their applications in gas capture, separations, and nanomaterial synthesis. However, their exact solvent structure still remains a mystery. We present the first chemical mapping of a SWIL solvent structure using in situ time-of-flight secondary ion mass spectrometry. In situ chemical mapping discovers two coexisting liquid phases and molecular structures vastly different from conventional ionic liquids. SWIL chemical speciation is found to be more complex than the known stoichiometry. Dimers and ionic clusters have been identified in SIMS spectra; and confirmed to be the chemical species differentiating from non-ionic liquids via spectral principal component analysis. Our unique in situ molecular imaging has advanced the understanding of SWIL chemistry and how this "heterogeneous" liquid structure may impact SWILs' physical and thermodynamic properties and associated applications