Inverse CO2 /C2 H2 Separation with MFU-4 and Selectivity Reversal via Postsynthetic Ligand Exchange.

Although many porous materials, including metal-organic frameworks (MOFs), have been reported to selectively adsorb C2 H2 in C2 H2 /CO2 separation processes, CO2 -selective sorbents are much less common. Here, we report the remarkable performance of MFU-4 (Zn5 Cl4 (bbta)3 , bbta=benzo-1,2,4,5-bistriazolate) toward inverse CO2 /C2 H2 separation. The MOF facilitates kinetic separation of CO2 from C2 H2 , enabling the generation of high purity C2 H2 (>98 %) with good productivity in dynamic breakthrough experiments. Adsorption kinetics measurements and computational studies show C2 H2 is excluded from MFU-4 by narrow pore windows formed by Zn-Cl groups. Postsynthetic F- /Cl- ligand exchange was used to synthesize an analogue (MFU-4-F) with expanded pore apertures, resulting in equilibrium C2 H2 /CO2 separation with reversed selectivity compared to MFU-4. MFU-4-F also exhibits a remarkably high C2 H2 adsorption capacity (6.7 mmol g-1 ), allowing fuel grade C2 H2 (98 % purity) to be harvested from C2 H2 /CO2 mixtures by room temperature desorption.

Unraveling the electrocatalytic reduction mechanism of enols on copper in aqueous media.

Deoxygenation of aldehydes and their tautomers to alkenes and alkanes has implications in refining biomass-derived fuels for use as transportation fuel. Electrochemical deoxygenation in ambient, aqueous solution is also a potential green synthesis strategy for terminal olefins. In this manuscript, direct electrochemical conversion of vinyl alcohol and acetaldehyde on polycrystalline Cu to ethanol, ethylene and ethane; and propenol and propionaldehyde to propanol, propene and propane is reported. Sensitive detection was achieved using a rotating disk electrode coupled with gas chromatography-mass spectrometry. In-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy, and in-situ Raman spectroscopy confirmed the adsorption of the vinyl alcohol. Calculations using canonical and grand-canonical density functional theory and experimental findings suggest that the rate-determining step for ethylene and ethane formation is an electron transfer step to the adsorbed vinyl alcohol. Finally, we extend our conclusions to the enol reaction from higher-order soluble aldehyde and ketone. The products observed from the reduction reaction also sheds insights into plausible reaction pathways of CO2 to C2 and C3 products.