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Effect of Electrolyte Ions on Iridium Oxide-Based Water Oxidation Catalysis
The oxygen evolution reaction often limits the efficiency of renewable fuel syntheses due to its sluggish reaction kinetics. Of the factors that have been studied to improve this important reaction is how the choice of the electrolyte may alter the reaction kinetics. Despite its importance, sys-tematic studies of this effect have been relatively rare. Herein, we report an effort toward correcting this deficiency by investigating the effect of nitrate on water oxidation catalyzed by IrO x . The results show that nitrate can suppress the reaction, resulting in a decrease of the rate and an increase in the Tafel slope. The effect was found to be consistent with a microkinetic model incorporating competitive adsorption between reac-tion intermediates and nitrate, suggesting that the reaction mechanism was unaffected by anion identity. Moreover, this blocking effect exhibited dependence on the cations, following a trend Li + ≈ Na + ≈ K + > Cs + > TEA + . The results are expected to find broad applications in electrocatalysis.
Intercalation of Cobalt into the Interlayer of Birnessite Improves Oxygen Evolution Catalysis
Here we show that the activity of cobalt for the oxygen evolution reaction (OER) can be enhanced by confining it in the interlayer region of birnessite (layered manganese oxide). The cobalt intercalation was verified by employing state-of-the-art characterization techniques such as XRD, Raman and electron microscopy. It is demonstrated that the Co 2+ /birnessite electrocatalyst can reach 10 mA cm -2 at an overpotential of 360 mV with near unity Faradaic efficiency. This overpotential is lower than that which can be achieved by using a pure cobalt hydroxide electrocatalyst for the OER. Furthermore, the Co 2+ /birnessite catalyst shows no degradation after 1000 electrochemical cycles.
Computational Optimization of Electric Fields for Improving Catalysis of a Designed Kemp Eliminase
Here we report a computational method to improve efficiency of a de novo designed Kemp eliminase enzyme KE15, by identifying mutations that enhance electric fields and chemical positioning of the substrate that contribute to free energy stabilization of the transition state. Starting from the design that has a k cat /K M of 27 M -1 s -1 , the most improved variant introduced four computationally targeted mutations to yield a k cat /K M of 403 M -1 s -1 , with almost all of the enzyme improvement realized through a 43-fold improvement in k cat , indicative of a direct impact on the chemical step. This work raises the prospect of computationally designing enzymes that achieve better efficiency with more minimal experimental intervention using electric field optimization as guidance.
Cooperative Catalysis by Surface Lewis Acid/Silanol for Selective Fructose Etherification on Sn-SPP Zeolite
While Lewis-acid zeolites, such as Sn-Beta, catalyze glucose isomerization in an alcoholic medium, mesoporous Sn-SPP catalyzes both glucose isomerization to fructose and fructose etherification (formally ketalization) to ethyl fructoside, enabling fructose yields in excess of the glucose/fructose equilibrium. Using periodic density functional theory calculations and force-field-based Monte Carlo simulations, the ketalization reaction mechanism and adsorption behavior were examined. The silanols on the Sn-SPP mesopore surface facilitate the ketalization reaction through hydrogen bonding interactions at the transition state, only possible via a Sn–O–Si–OH moiety, present in Sn-SPP but not in Sn-Beta. Fructose ketalization is favored over glucose acetalization due to differences in stability of the oxonium intermediates, which are stabilized by the Sn-SPP active site. The open site of hydrophobic Sn-Beta cannot perform these reactions because its active site does not contain an adjacent silanol of the right geometry. Finally, in addition to the more favorable activation barrier of the catalytic process, the adsorption at the catalytic site in Sn-SPP is also found to be more favorable than for Sn-Beta, in spite of competitive adsorption between fructose and ethanol in the ethanol-saturated zeolites.
A Voltammetric Study of Nitrogenase Catalysis Using Electron Transfer Mediators
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Autoxidation Catalysis for Carbon–Carbon Bond Cleavage in Lignin
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Living additive manufacturing: Transformation of parent gels into diversely functionalized daughter gels made possible by visible light photoredox catalysis
Light-initiated additive manufacturing techniques typically rely on layer-by-layer addition or continuous extraction of polymers formed via nonliving, free radical polymerization methods that render the final materials “dead” toward further monomer insertion; the polymer chains within the materials cannot be reactivated to induce chain extension. An alternative “living additive manufacturing” strategy would involve the use of photocontrolled living radical polymerization to spatiotemporally insert monomers into dormant “parent” materials to generate more complex and diversely functionalized “daughter” materials. Here, we demonstrate a proof-of-concept study of living additive manufacturing using end-linked polymer gels embedded with trithiocarbonate iniferters that can be activated by photoinduced single-electron transfer from an organic photoredox catalyst in solution. This system enables the synthesis of a wide range of chemically and mechanically differentiated daughter gels from a single type of parent gel via light-controlled modification of the parent’s average composition, strand length, and/or cross-linking density. Furthermore, daughter gels that are softer than their parent, stiffer than their parent, larger but with the same modulus as their parent, thermally responsive, polarity responsive, healable, and weldable are all realized.
Heterogeneous Epoxide Carbonylation by Cooperative Ion-Pair Catalysis in Co(CO) 4 – -Incorporated Cr-MIL-101
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