In recent years, electrochemical reduction of carbon dioxide (CO2) has received a great deal of attention due to the potential that this process can mitigate the atmospheric CO2 concentration and ...produce valuable organic compounds. In particular, Cu and Cu-based catalysts have exhibited the capability of converting CO2 into multicarbon fuels and chemicals in significant quantities. Here, we report a facile and cheap fabrication method for the development of an Ag-incorporated cuprous oxide (Ag-Cu2O) electrode enabling selective synthesis of ethanol via electrochemical CO2 reduction and reveal the key factor improving the ethanol (C2H5OH) selectivity. The incorporation of Ag into Cu2O leads to the suppression of hydrogen (H2) evolution, and furthermore, by varying the elemental arrangement (phase-separated and phase-blended) of Ag and Cu, we observe that C2H5OH selectivity can be controlled. Consequently, the Faradaic efficiency for C2H5OH on phase-blended Ag-Cu2O (Ag-Cu2OPB) is 3 times higher than that of the Cu2O without Ag dopant. We propose that the electrochemical reaction behavior is not solely associated with a role of Ag dopant, carbon monoxide (CO) leading to an ethanol formation pathway over ethylene, but also the doping pattern related population of Ag-Cu biphasic boundaries relatively suppresses the H2 evolution reaction and encourages the reaction of mobile CO generated on Ag to a residual intermediate on a Cu site.
In this paper, the effect of pre-treatment and calcination temperature on a series of 5%Co/Al2O3-ZrO2, 5%Ni/Al2O3-ZrO2 and 2.5%Co-2.5%Ni/Al2O3-ZrO2 catalysts for dry reforming of methane was ...investigated. Main focus of our research was to improve the catalyst stability by proper pre-treatment and reaction conditions. The first approach aimed at the catalyst pre-treatment by using bimetallic systems and the second strategy at the in situ suppression of coke. The catalytic activity of bimetallic system was indeed higher compared to the monometallic in the temperature range of 500–800 °C (space velocity 18000 ml h−1·gcat−1, CH4/CO2 = 1). The bimetallic catalyst calcined at 800 °C showed highest CH4 conversion without deactivation and gave a H2/CO ratio of 91% and 0.96, respectively, and good stability with less coke deposition over 28 h at 800 °C reaction temperature. This improvement is assigned to the synergism between Co and Ni, their high dispersion according to interaction with support. It has been shown in our work that pretreatment temperatures and atmospheres have strong impact on stability of the catalyst. TEM, XRD and TPO investigations confirmed that the slight catalyst deactivation was related to the formation of multiwall carbon nanotubes with hollow inner tube structure. The addition of small amounts of steam or oxygen during DRM improved both the catalyst activity and stability as the bimetallic catalyst lost around 9.4% conversion in DRM, 5.4% in presence of water and only 3.2% in presence of O2.
•2.5%Co-2.5%Ni/Al2O3-ZrO2 catalyst calcined at 800 °C showed higher activity.•2.5%Co-2.5%Ni/Al2O3-ZrO2 had less coke deposition for 28 h reaction time.•The CoNi-4 catalyst is capable of operating under different feed compositions.•CoNi-4 catalyst activity is improved by addition of small amount of steam or O2.
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Bimetallic catalysts often outperform monometallic catalysts due to changeable structural orientation, synergistic effects, and integration of two different metal or metal oxide ...properties. Here, a series of CeO2 nanorods (NR) supported bimetallic CuOx and RuOx catalysts (Cu: Ru ratios of 9:1, 7:3, and 5:5) were prepared using a wet impregnation method. In situ DRIFTS, H2 temperature programmed reduction (H2-TPR), CO temperature programmed desorption (CO-TPD), and other characterization techniques were used to investigate the effect of the Cu:Ru ratio on the activity of low-temperature CO oxidation. Among three catalysts, CeO2 NR supported 7 wt% Cu-3 wt% Ru catalyst after a reduction activation treatment showed the best performance with 100 % CO conversion at 166 °C and the lowest activation energy of 18.37 kJ mol−1. Raman and XPS profiles revealed that the origin of the superior performance is at least partially related to the high surface oxygen vacancy concentration and other distinct oxygen species (physi-/chemi-sorbed oxygen and bulk lattice oxygen), leading to outstanding adsorption and oxidation property of CO.
We report a selective and stable electrocatalyst utilizing non-noble metals consisting of Cu and Sn for the efficient and selective reduction of CO2 to CO over a wide potential range. The bimetallic ...electrode was prepared through the electrodeposition of Sn species on the surface of oxide-derived copper (OD-Cu). The Cu surface, when decorated with an optimal amount of Sn, resulted in a Faradaic efficiency (FE) for CO greater than 90% and a current density of −1.0 mA cm–2 at −0.6 V vs RHE, compared to the CO FE of 63% and −2.1 mA cm–2 for OD-Cu. Excess Sn on the surface caused H2 evolution with a decreased current density. X-ray diffraction (XRD) suggests the formation of Cu–Sn alloy. Auger electron spectroscopy of the sample surface exhibits zerovalent Cu and Sn after the electrodeposition step. Density functional theory (DFT) calculations show that replacing a single Cu atom with a Sn atom leaves the d-band orbitals mostly unperturbed, signifying no dramatic shifts in the bulk electronic structure. However, the Sn atom discomposes the multifold sites on pure Cu, disfavoring the adsorption of H and leaving the adsorption of CO relatively unperturbed. Our catalytic results along with DFT calculations indicate that the presence of Sn on reduced OD-Cu diminishes the hydrogenation capabilityi.e., the selectivity toward H2 and HCOOHwhile hardly affects the CO productivity. While the pristine monometallic surfaces (both Cu and Sn) fail to selectively reduce CO2, the Cu–Sn bimetallic electrocatalyst generates a surface that inhibits adsorbed H*, resulting in improved CO FE. This study presents a strategy to provide low-cost non-noble metals that can be utilized as a highly selective electrocatalyst for the efficient aqueous reduction of CO2.
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•A novel CoFe/CoFe2O4@NGF cathode with heterointerfaces was synthesized.•CoFe/CoFe2O4 heterointerfaces contribute to strengthening electron transfer.•Valence cycles of Co/Fe are ...stable via interfacial electron transfer.•The kinetic constant of CoFe/CoFe2O4@NGF cathode is 23 times higher than GF.•The possible degradation pathway and catalytic mechanism were proposed.
The inefficient electron transfer and Fe(III)/Fe(II) cycle remain significant obstacles in the electro-fenton process. Herein, a nitrogen-doped graphite felt (NGF)-supported CoFe/CoFe2O4 heterostructure is synthesized that achieves highly efficient interfacial electron transfer and stable Co/Fe redox cycle. Theoretical calculations demonstrate that the CoFe/CoFe2O4 heterointerfaces induce local charge redistribution benefiting from the electronic communication between electron acceptor (CoFe2O4) and electron donor (CoFe). Analysis of the Fermi level indicates that the introduction of CoFe alloy enhances the electron density of the catalyst. The CoFe/CoFe2O4@NGF cathode can remove bisphenol A (BPA) completely in 90 min, and the pseudo-first-order kinetic constant (0.0625 min−1) is 23 times higher than the GF system. Notably, the CoFe/CoFe2O4@NGF electrode maintains excellent catalytic capability and stability within a broad pH range (3–11). The construction of the CoFe/CoFe2O4 heterostructure reduces the adsorption energy of oxygen, which ultimately increases the yield of reactive oxygen species (ROS). Quenching experiments revealed that hydroxyl radical (·OH) played a dominant role in the degradation of BPA, and significantly reduced the biotoxicity of intermediate products. This work offers a dependable approach for developing bimetallic catalysts with high catalytic activity.
A variety of metal elements have exhibited strong reductive and dehalogenative capabilities for the removal of persistent organic pollutants, owing to electron transfer or electron-hole activation ...through various methods. Herein, a bimetallic CNi-Al2O3 structure (AlCNi) was successfully synthesized to simultaneously function as sorbent and catalyst in the reduction of perfluoroalkyl carboxylic acids (PFOA) polluted wastewater. Using a reaction period of 3 h, 98% of PFOA was removed by AlCNi through a mechanochemical stirring method and 70.43% of fluorine ions was released from PFOA anchored onto the surface of AlCNi. Both thermocatalysis and photocatalysis technologies were incorporated and compared when utilized in tandem with AlCNi to mitigate the PFOA. In addition, peroxymonosulfate (PMS) and sodium sulfite (Na2SO3) were also integrated into experiments, separately, as a strong oxidant and reductant to improve the degradation effect of PFOA. However, the degradation efficiency of both were lower than that of AlCNi, even when assisted by elevated temperatures and ultraviolet irradiation. The feasibility of employing AlCNi for PFOA degradation was further investigated at various temperature and pH conditions. The data obtained from HPLC-MS/MS, TOC, and IC with multiple characterizations of AlCNi/PFOA, proposed the predominant degradation pathways comprising adsorption, defluorination-hydroxylation, and decarboxylation. This study provides a valuable remediation method without utilizing chemical agents and special activation for PFOA by AlCNi, which can be suitable for large-scale sewage treatment applications.
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•A bimetallic Al2O3-Ni structure supported on graphite carbon was synthesized and characterized.•98% of PFOA was effectively removed by AlCNi without resorting to any chemical agent.•PFOA was anchored on the surface of AlCNi in a monodentate ligand and then followed by electron attack during degradation.•A small amount of superoxide radicals was present in this system.
Development of highly effective catalysts for selective hydrodeoxygenation (HDO) of syringol, a model compound of lignin, to cyclohexanol (CYHAOL) is a challenge due to the intricate molecular ...structure of syringol. Herein, we have synthesized an in–situ activated cobalt–silver bimetallic catalyst, CoAg/SiO2, through a simple incipient–wetness impregnation method. The catalyst without pre–reduction treatment attained a complete conversion with 93.8 mol% CYHAOL selectivity under moderate reaction conditions. Characterizations including HRTEM, XPS, XRD, NH3–TPD, and H2–TPR unanimously revealed the structure–activity relationship of the catalyst. In the reaction system, Ag promoted the in–situ reduction of Co3O4 to form a polycrystalline–structure complex (CoOx) containing oxygen vacancies. Ag also combines with Co to construct strong acid sites. The synergy of CoOx, oxygen vacancies, Ag, and acid sites demonstrates a high–efficiency HDO of syringol to CYHAOL. CoAg/SiO2 exonerates the pre–reduction treatment, simplifying the preparation and maintenance process and preventing severe sintering of the metals.
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•An in–situ activated CoAg/SiO2 catalyst has been synthesized through a simple incipient–wetness impregnation method.•CoAg/SiO2 without pre–reduction treatment attained excellent performance in HDO of syringol to cyclohexanol.•Ag promotes Co3O4 in–situ reduction to CoOx polycrystalline with oxygen vacancies in the reaction system.•Ag also combines with Co to construct strong acid sites.•The synergy of CoOx, oxygen vacancies, Ag, and acid sites demonstrates the efficient catalytic function.
Nitrate (NO3 −) is an ubiquitous groundwater contaminant and is detrimental to human health. Bimetallic palladium-based catalysts have been found to be promising for treating nitrate (and nitrite, ...NO2 −) contaminated waters. Those containing indium (In) are unusually active, but the mechanistic explanation for catalyst performance remains largely unproven. We report that In deposited on Pd nanoparticles (NPs) (“In-on-Pd NPs”) shows room-temperature nitrate catalytic reduction activity that varies with volcano-shape dependence on In surface coverage. The most active catalyst had an In surface coverage of 40%, with a pseudo-first order normalized rate constant of k cat ∼ 7.6 L gsurface-metal −1 min−1, whereas monometallic Pd NPs and In2O3 have nondetectible activity for nitrate reduction. X-ray absorption spectroscopy (XAS) results indicated that In is in oxidized form in the as-synthesized catalyst; it reduces to zerovalent metal in the presence of H2 and reoxidizes following NO3 − contact. Selectivity in excess of 95% to nontoxic N2 was observed for all the catalysts. Density functional theory (DFT) simulations suggest that submonolayer coverage amounts of metallic In provide strong binding sites for nitrate adsorption and they lower the activation barrier for the nitrate-to-nitrite reduction step. This improved understanding of the In active site expands the prospects of improved denitrification using metal-on-metal catalysts.
•Low concentration Pd and Rh promoted Ni/Al2O3 were tested in the NO+H2 reaction.•Promotion by Pd or Rh enhances the metal dispersion.•Molecularly and dissociatively adsorbed NO coexist on the ...catalysts (NO-TPD).•Promoted catalysts present superior catalytic activity in the NO+H2 reaction.•Ni–Pd/Al2O3 is the most efficient and stable catalyst in the reduction of NO by H2.
Three Ni based catalysts, Ni(10wt.%)/Al2O3, Ni(10wt.%)–Pd(0.5wt.%)/Al2O3, and Ni(10wt.%)–Rh(0.5wt.%)/Al2O3, were comparatively tested in the catalytic reduction of NO by hydrogen. Catalytic activity tests consisted in temperature programmed reactions (TPRea) under plug flow conditions, in the 50–350°C temperature range, with a rate of 5°C/min. The feed stream corresponded to a reactant ratio of NO:H2=1:1.3 and a GHSV of 4500h−1. Catalytic activity results proved that promotion with low concentrations of both Pd and Rh increases the catalytic performances of the Ni based catalyst, in respect to NO conversion, N2 selectivity and N2 yield. By far, the most efficient catalyst in the NO+H2 reaction proved to be Ni–Pd/Al2O3, with NO conversions greater than 95% and N2 selectivity of at least 90% at T⩾100°C. Stability tests confirmed the Pd promoted catalyst as the most efficient one in the investigated series. The catalytic performance in terms of N2 selectivity/yield for the Ni–Rh/Al2O3 catalyst proved to be only slightly superior to that corresponding to Ni/Al2O3, although both Ni and Rh are efficient in the dissociative adsorption of NO (NO-TPD).
The mono- and bimetallic catalysts were characterized by different investigation techniques such as: N2 adsorption–desorption isotherms at −196°C (BET), X-ray powder diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption of hydrogen (H2-TPD) and NO (NO-TPD). Characterization techniques revealed that promotion with small amounts of Pd or Rh enhances the reducibility of the supported NiO in the catalyst precursor, as well as the dispersion of the metal on the catalyst surface.
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