Dual-Facet Mechanism in Copper Nanocubes for Electrochemical CO2 Reduction into Ethylene

The product selectivity in the electrochemical reduction of carbon dioxide depends on the structure of the copper electrode. Cube-shaped copper catalysts, enclosed by {100} terraces, {110} edges, and {111} corners, exhibit a size-dependent enhanced only selectivity toward C-2 products and ethylene in particular. However, the underlying chemical reasons for such a behavior are not fully understood. This computational work toward ethylene formation investigates the carbon dioxide electroreduction mechanism over copper nanocubes. The analysis of the different pathways illustrates that the thermodynamic picture is limited in describing the formation of this product. Based on the activation barriers associated with the limiting C-2 formation step, we identify a dual-facet mechanism occurring at the interface between the {100} terraces and {110} edges. These results highlight that the reactivity of shape-controlled nanocatalysts goes beyond the facet-selectivity observed in single crystals owing to the possible synergies arising at the intersection between the enclosing crystalline planes.

Metal-organic framework derived copper catalysts for CO2 to ethylene conversion

Jun Li, Ning Wang

The electrochemical reduction of CO2 to ethylene provides a carbon-neutral avenue for the conversion of CO2 to value-added fuels and feedstocks, so contributing to the storage of intermittent renewable electricity. The exploration of efficient electrocatalysts with high ethylene selectivity and productivity is highly desirable but remains challenging. Here, we present a Cu-based catalyst derived from a metal-organic framework (Cu-MOF) which shows enhanced performance due to its porous morphology, complex oxidation states and strong lattice strain. X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy are utilized to track the evolution of the crystal structure and oxidation states during the reaction, and the results reveal that Cu2+ ions are rapidly reduced to Cu+ and then slowly to Cu-0, resulting in a Cu@CuxO core@shell structure. The tensile strain caused by the distorted grain is beneficial for the activation of CO2. Cu+/Cu-0 interfaces formed through stabilized Cu+ facilitate *CO-CO dimerization, promoting conversion to C2+ products and suppressing conversion to C-1 products. The optimized catalyst exhibits a 51% Faraday efficiency (FE) for ethylene and a 70% FE for C2+ products, with 20 h operational stability in an H-cell configuration, and a partial ethylene current density of 150mA cm(-2) in a flow-cell configuration.

ROYAL SOC CHEMISTRY2020

Impact of organic-ligand shell on catalytic performance of colloidal Pd nanoparticles for alkyne gas-phase hydrogenation

Fernando Cardenas Lizana, Lioubov Kiwi, Daniel André Samuel Lamey, Irina Prokopyeva

Monodispersed Pd nanoparticles (NPs) have been prepared by colloidal technique and deposited on a structured support consisting of carbon nanofibers (CNF) grown on sintered metal fibres (SMF). The surface properties of Pd NPs have been fine-tuned by (i) changing the nature of stabilizing agent (electrostatic vs. steric), (ii) controlling Pd NPs size (2-10 nm) and (iii) grafting N-containing ligands onto the CNF/SMF surface. In the semi-hydrogenation of acetylene (T= 393 K; 13= 1 bar) catalytic response was insensitive to the nature of the reducing agent where equivalent activity/selectivity were obtained over Pd NPs with similar dispersion, prepared with the same stabilizer. A similar product distribution was recorded over Pd NPs with similar crystal size irrespective of the colloidal stabilizer (electrostatic vs. steric). In contrast, a stronger inhibiting effect on hydrogenation rate has been found with electrostatic stabilizer (sodium di-2-ethylhexylsulfosuccinate) as compared to the steric ones (polyvinylpyrrolidone or polyvinylalcohol) and assigned to geometric and electronic effects. Decrease (from 8 2 nm) in Pd NPs size results in a concomitant decrease in activity (antipathetic size-sensitivity), but higher selectivity to target ethylene product. Grafting of nitrogen-containing modifiers (polyvinylpyridine or polyethylenimine) on the CNF/SMF support results in a significant increase in olefin selectivity (up to 93%) where the catalyst shows remarkable stability during 120 h on-stream. This is explained by the electronic modifications promoted by interactions between the Pd NPs and the grafted ligands as confirmed by XPS analysis. In comparison, stabilizer-free Pd/CNF/SMF has low selectivity to ethylene (65%). In summary, controlled size Pd (core) nanoparticles with organic ligands ( shell) demonstrated increased selectivity and remarkable stability in catalytic gas-phase alkyne semi-hydrogenation opening new tools for rational catalyst design. (C) 2014 Elsevier B.V. All rights reserved.

Elsevier2014

Selective C-C Coupling in Carbon Dioxide Electroreduction via Efficient Spillover of Intermediates As Supported by Operando Raman Spectroscopy

Jing Gao, Jingshan Luo, Dan Ren, Shaik Mohammed Zakeeruddin, Hong Zhang

Developing efficient systems for the conversion of carbon dioxide to valuable chemicals using solar power is critical for mitigating climate change and ascertaining the worlds future supply of clean fuels. Here, we introduce a mesoscopic cathode consisting of Cu nanowires decorated with Ag islands, by the reduction of Ag-covered Cu2O nanowires prepared via galvanic replacement reaction. This catalyst enables CO2 reduction to ethylene and other C2+ products with a faradaic efficiency of 76%. Operando Raman spectroscopy reveals intermediate formation of CO at Ag sites which undergo subsequent spillover and hydrogenation on the Cu nanowires. Our Cu-Ag bimetallic design enables a similar to 95% efficient spillover of intermediates from Ag to Cu, delivering an improved activity toward the formation of ethylene and other C2+ products. We also demonstrate a solar to ethylene conversion efficiency of 4.2% for the photoelectrochemical CO2 reduction using water as electron and proton donor, and solar power together with perovskite photovoltaics to drive the uphill reaction.

AMER CHEMICAL SOC2019

Impact of organic-ligand shell on catalytic performance of colloidal Pd nanoparticles for alkyne gas-phase hydrogenation

Fernando Cardenas Lizana, Lioubov Kiwi, Daniel André Samuel Lamey, Irina Prokopyeva

Elsevier2014