Effective methane utilization for either clean power generation or value-added chemical production has been a subject of growing attention worldwide for decades, yet challenges persist mostly in relation to methane activation under mild conditions. Here, we report hematite, an earth-abundant material, to be highly effective and thermally stable to catalyze methane combustion at low temperatures (<500 °C) with a low light-off temperature of 230 °C and 100% selectivity to CO 2 . The reported performance is impressive and comparable to those of precious-metal-based catalysts, with a low apparent activation energy of 17.60 kcal• mol −1 . Our theoretical analysis shows that the excellent performance stems from a tetra-iron center with an antiferromagnetically coupled iron dimer on the hematite (110) surface, analogous to that of the methanotroph enzyme methane monooxygenase that activates methane at ambient conditions in nature. Isotopic oxygen tracer experiments support a Mars van Krevelen redox mechanism where CH 4 is activated by reaction with a hematite surface oxygen first, followed by a catalytic cycle through a molecular-dioxygen-assisted pathway. Surface studies with in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations reveal the evolution of reaction intermediates from a methoxy CH 3 − O−Fe, to a bridging bidentate formate b-HCOO−Fe, to a monodentate formate m-HCOO−Fe, before CO 2 is eventually formed via a combination of thermal hydrogen-atom transfer (HAT) and proton-coupled electron transfer (PCET) processes. The elucidation of the reaction mechanism and the intermediate evolutionary profile may allow future development of catalytic syntheses of oxygenated products from CH 4 in gas-phase heterogeneous catalysis.

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Heterogenization of homogenous catalysts on electrode surfaces provides a valuable approach for characterization of catalytic processes in operando conditions using surface selective spectroelectrochemistry methods. Ligand design plays a central role in the attachment mode and the resulting functionality of the heterogenized catalyst as determined by the orientation of the catalyst relative to the surface and the nature of specific interactions that modulate the redox properties under the heterogeneous electrode conditions. Here, we introduce new [Re(L)(CO) 3 Cl] catalysts for CO 2 reduction with sulfur-based anchoring groups on a bipyridyl ligand, where L = 3,3 ′-disulfide-2,2 ′-bipyridine (SSbpy) and 3,3 ′-thio-2,2 ′-bipyridine (Sbpy). Spectroscopic and electrochemical analysis complemented by computational modeling at the density functional theory level identify the complex [Re(SSbpy)(CO) 3 Cl] as a multi-electron acceptor that combines the redox properties of both the rhenium tricarbonyl core and the disulfide functional group on the bipyridyl ligand. The first reduction at −0.85 V (vs. SCE) involves a two-electron process that breaks the disulfide bond, activating it for surface attachment. The heterogenized complex exhibits robust anchoring on gold surfaces, as probed by vibrational sum-frequency generation (SFG) spectroscopy. The binding configuration is normal to the surface, exposing the active site to the CO 2 substrate in solution. The attachment mode is thus particularly suitable for electrocatalytic CO 2 reduction.

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Metal–ligand complexes have been extensively explored as well-defined molecular catalysts in small molecule activation reactions such as carbon dioxide (CO2) reduction. Many hybrid photocatalysts have been prepared by coupling such complexes with photoactive surfaces for use in solar CO2 reduction. In this work, we employ X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies, density functional theory (DFT) and computational XANES modeling to interrogate the structure of a hybrid photocatalyst consisting of a macrocyclic cobalt complex deposited on graphitic carbon nitride (C3N4). Results show that the cobalt complex binds on C3N4 through surface OH or NH2 groups. By refining the local geometry and binding sites of this well-defined molecular cobalt complex on C3N4, we established an important benchmark for modeling a large class of molecular catalysts that can be adapted to in situ/operando studies and further enhanced by applying chemometrics-based approaches and machine learning methods of XANES data analysis.

We detail the development of the first enantioselective synthetic route to euonyminol (1), the most heavily oxidized member of the dihydro-β-agarofuran sesquiterpenes and the nucleus of the macrocyclic alkaloids known as the cathedulins. Key steps in the synthetic sequence include a novel, formal oxyalkylation reaction of an allylic alcohol by [3 + 2] cycloaddition; a tandem lactonization−epoxide opening reaction to form the trans-C2−C3 vicinal diol residue; and a late-stage diastereoselective trimethylaluminum-mediated α-ketol rearrangement. We report an improved synthesis of the advanced unsaturated ketone intermediate 64 by means of a 6-endo-dig radical cyclization of the enyne 42. This strategy nearly doubled the yield through the intermediate steps in the synthesis and avoided a problematic inversion of stereochemistry required in the first-generation approach. Computational studies suggest that the mechanism of this transformation proceeds via a direct 6-endo-trig cyclization, although a competing 5-exo-trig cyclization, followed by a rearrangement, is also energetically viable. We also detail the challenges associated with manipulating the oxidation state of late-stage intermediates, which may inform efforts to access other derivatives such as 9-epieuonyminol or 8-epi-euonyminol. Our successful synthetic strategy provides a foundation to synthesize the more complex cathedulins.

A well-known catalyst, fac-Re(4,4′-R 2 -bpy)(CO) 3 Cl (bpy = bipyridine; R = COOH) (ReC0A), has been widely studied for CO 2 reduction; however, its photocatalytic performance is limited due to its narrow absorption range. Quantum dots (QDs) are efficient light harvesters that offer several advantages, including size tunability and broad absorption in the solar spectrum. Therefore, photoinduced CO 2 reduction over a broad range of the solar spectrum could be enabled by ReC0A catalysts heterogenized on QDs. Here, we investigate interfacial electron transfer from Cd 3 P 2 QDs to ReC0A complexes covalently bound on the QD surface, induced by photoexcitation of the QD. We explore the effect of triethylamine, a sacrificial hole scavenger incorporated to replenish the QD with electrons. Through combined transient absorption spectroscopic and computational studies, we demonstrate that electron transfer from Cd 3 P 2 to ReC0A can be enhanced by a factor of ∼4 upon addition of triethylamine. We hypothesize that the rate enhancement is a result of triethylamine possibly altering the energetics of the Cd 3 P 2 −ReC0A system by interacting with the quantum dot surface, deprotonation of the quantum dot, and preferential solvation, resulting in a shift of the conduction band edge to more negative potentials. We also observe the rate enhancement in other QD−electron acceptor systems. Our findings provide mechanistic insights into hole scavenger−quantum dot interactions and how they may influence photoinduced interfacial electron transfer processes.