Topic
Selectivity
About: Selectivity is a research topic. Over the lifetime, 9445 publications have been published within this topic receiving 227360 citations.
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11 Jun 2018
TL;DR: In this paper, a class of core-shell vacancy engineering catalysts that utilize sulfur atoms in the nanoparticle core and copper vacancies in the shell to achieve efficient electrochemical CO2 reduction to propanol and ethanol was proposed.
Abstract: Engineering copper-based catalysts that favour high-value alcohols is desired in view of the energy density, ready transport and established use of these liquid fuels. In the design of catalysts, much progress has been made to target the C–C coupling step; whereas comparatively little effort has been expended to target post-C–C coupling reaction intermediates. Here we report a class of core–shell vacancy engineering catalysts that utilize sulfur atoms in the nanoparticle core and copper vacancies in the shell to achieve efficient electrochemical CO2 reduction to propanol and ethanol. These catalysts shift selectivity away from the competing ethylene reaction and towards liquid alcohols. We increase the alcohol-to-ethylene ratio more than sixfold compared with bare-copper nanoparticles, highlighting an alternative approach to electroproduce alcohols instead of alkenes. We achieve a C2+ alcohol production rate of 126 ± 5 mA cm−2 with a selectivity of 32 ± 1% Faradaic efficiency. The conversion of carbon dioxide into multi-carbon alcohols would enable the synthesis of sustainable liquid fuels with high energy densities. Now, vacancy-engineered core–shell copper-based catalysts are able to shift the selectivity of electrochemical CO2 reduction into alcohols instead of alkenes, as obtained with bare-copper catalysts.
458 citations
456 citations
TL;DR: Online mass spectroscopy studies combined with X-ray diffraction data suggest the reduction of the Cu2O films in the presence of CO2, generating a nanoparticulate Cu morphology, prior to the production of hydrogen, CO, and hydrocarbons.
Abstract: The catalytic activity and hydrocarbon selectivity in electrochemical carbon dioxide (CO2) reduction on cuprous oxide (Cu2O) derived copper nanoparticles is discussed. Cuprous oxide films with [100], [110] and [111] orientation and variable thickness were electrodeposited by reduction of copper(II) lactate on commercially available copper plates. After initiation of the electrochemical CO2 reduction by these oxide structures, the selectivity of the process was found to largely depend on the parent Cu2O film thickness, rather than on the initial crystal orientation. Starting with thin Cu2O films, besides CO and hydrogen, selective formation of ethylene is observed with very high ethylene-to-methane ratios (8 to 12). In addition to these products, thicker Cu2O films yield a remarkably large amount of ethane. Long term Faradaic efficiency analysis of hydrocarbons shows no sign of deactivation of the electrodes after 5 hours of continuous experiment. Online mass spectroscopy studies combined with X-ray diffraction data suggest the reduction of the Cu2O films in the presence of CO2, generating a nanoparticulate Cu morphology, prior to the production of hydrogen, CO, and hydrocarbons. Optimizing coverage, number density and size of the copper nanoparticles, as well as local surface pH, may allow highly selective formation of the industrially important product ethylene
447 citations
TL;DR: Azo-bridged, nitrogen-rich, aromatic, water stable, nanoporous covalent organic polymers, which can be synthesized by catalyst-free direct coupling of aromatic nitro and amine moieties under basic conditions are reported, displaying an unprecedented increase in CO(2)/N(2) selectivity with increasing temperature.
Abstract: Porous materials are well studied for gas capture and separation technologies. Here, the authors report nitrogen-rich, nanoporous polymers, which display very high CO2/N2 selectivity with increasing temperature, which may be attributable to an entropically driven N2-phobicity effect.
445 citations
TL;DR: This work has used site-directed mutagenesis and single-channel recordings to identify a molecular region that influences ionic selectivity in a cloned A-type K+ channel from Drosophila and concludes that the H5 region is likely to line the pore of the K+ channels.
Abstract: THE high ionic selectivity of K+ channels is a unifying feature of this diverse class of membrane proteins. Though K+ channels differ widely in regulation and kinetics, physiological studies have suggested a common structure: a single file pore containing multiple ion-binding sites and having broader vestibules at both ends1–5. We have used site-directed mutagenesis and single-channel recordings to identify a molecular region that influences ionic selectivity in a cloned A-type K+ channel from Drosophila. Single ammo-acid substitutions in H5, the fifth hydrophobic region6, enhanced the passage of NH+4 and Rb+, ions with diameters larger than K+, without compromising the ability of the channel to exclude the smaller cation, Na+. The mutations that substantially altered selectivity had little effect on the gating properties of the channel. We conclude that the H5 region is likely to line the pore of the K+ channel.
431 citations