Cu has the highest atomic coordination number among metals and is therefore well-suited to electrochemically convert carbon dioxide (CO2) to various chemical feedstocks.cu catalyst However, the activity and selectivity toward CO2 reduction depends on surface sensitivity and electrokinetics.cu catalyst Hence, it is important to modify the structure and tune the crystal orientation in order to stabilize and enhance CO2 reductor performances.cu catalyst Surface engineering, such as controlled morphology, oxygen vacancies, alloys on supports or substrates, has been proven to be effective in controlling the structure-sensitivity and electrokinetics of copper catalysts.
A new method of improving copper catalysts for a very common process in industrial production, the synthesis of ammonia from ammonium nitrate, has recently been developed.cu catalyst Researchers at MIT have designed a novel type of copper-based catalyst that has been modified to reduce the energy needed for nitrate ions to attach to the catalyst.cu catalyst This modification significantly increases the number of available active sites, which allows electrons to move across the catalyst faster and more efficiently, thus allowing the nitrate ions to combine with nitrogen faster to form ammonia.cu catalyst
The MIT researchers used density functional theory calculations to determine that the structure of the nitrate ion changes its binding energy with the copper atoms in the catalyst, thus reducing the activation barrier for nitrogen-hydrogen bonding.cu catalyst They also found that changing the crystal orientation of the nitrate ion alters how the ions interact with other ions on the catalyst, which makes it easier for them to combine with nitrogen atoms and increase the rate of ammonia formation.cu catalyst
Moreover, they found that a certain type of copper-based alloy, which is composed of metallic Cu and CuPc, can also be effective in the nitrate synthesis reaction.cu catalyst cu catalyst The X-ray absorption fine structure (XAFS) spectrum of this copper-based alloy reveals that the metallic Cu peak is reduced in magnitude as the electrode potential is negatively polarized, while the peaks corresponding to the CuPc and Cu(0) species remain unaltered.cu catalyst The spectral features observed at the final electrode potential of -0.64 V closely resemble those of the initial OCV, which demonstrates that this change in the oxidation state is structurally reversible.
In another recent study, the same group at HKUST successfully utilized copper wire bits as a simple catalyst for a click chemistry reaction with supercritical CO2 (scCO2).cu catalyst This approach allowed them to avoid the use of organic solvents and obtain a clean and green product.cu catalyst
The researchers characterized the atomic composition of this copper-Sb-Pb-based catalyst using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) combined with energy-dispersive X-ray spectroscopy (EDS).cu catalyst Their results showed that the atomic distribution of Sb and Pd was even throughout the Cu matrix and did not show any noticeable aggregation, which is consistent with previous reports.cu catalyst In addition, they found that the catalyst exhibits good structural reversibility under CO2 reduction conditions, maintaining high faradaic efficiency (FE) for C2H4 for over 60 hours. This suggests that the surface-restructuring process induced by CO2 reduction can be a powerful strategy for stabilizing Cu-based electrocatalysts against deactivation by carbonaceous species accumulation.
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