CO Insertion Research Articles

Electrochemical CO2/CO Reduction and C–C Coupling Path for Mimicking Fischer–Tropsch Synthesis over Cadmium Electrodes

Converting CO2 into Cn>2 hydrocarbons has been a significant challenge, but recent research has shown that cadmium (Cd) can be used to produce C2–7 hydrocarbons (CnH2n and CnH2n+2) directly through electrochemical CO2 reduction in a K2HPO4/KH2PO4 buffer. The production of hydrocarbons was found to be enhanced by engineering the interface of the Cd surface with other transition metals. This process imitates the Fischer–Tropsch (F–T) synthesis, which involves surface polymerization reactions that couple carbon atoms together, resulting in the formation of long-chain hydrocarbons via the insertion of CO and CHx molecules. While the formate path was almost completely suppressed, the CO path remained. While the current Faradaic efficiency may be low, this study highlights the potential of electrochemical CO reduction for Cd. The study demonstrates that CO and H can directly participate in F–T synthesis through electrochemistry. Furthermore, Cd was observed to recrystallize into stacked wall structures resembling flowers after the electrochemical process. As a result, this research provides crucial insights that can aid in a better understanding of C–C coupling paths via electrochemistry.

Electrochemical CO2 reduction versus CO reduction over Au/Ti electrocatalyts in phosphate buffer condition

Au supported on Ti has gained popularity as a highly stable and efficient catalyst in various fields. In this study, we report the use of Au/Ti as electrocatalysts for both electrochemical (EC) CO2 reduction and CO reduction in a phosphate buffer electrolyte. We demonstrate, for the first time, that the dominant gas products are CO, H2, and CH4, and that the EC CO2 reduction process yields long-chain hydrocarbons (CnH2n and CnH2n+2, n = 2–7) resulting from initial CO2 adsorption. Similarly, CH4 and long-chain hydrocarbons are significantly produced by EC CO reduction via direct CO adsorption on the catalyst surface. We also demonstrate an EC method for mimicking Fischer-Tropsch synthesis, which involves both indirect CO2 and direct CO adsorptions. By analyzing the weight distribution using the Anderson-Schulz-Flory method, we were able to understand the surface polymerization reaction, which we attributed to CO and CHx insertion. These findings are highly unique and represent a significant advancement in the development of electrochemical methods and electrocatalysts for producing long-chain hydrocarbon fuels.

Size-dependent and sensitivity of copper particle in ternary CuZnAl catalyst for syngas to ethanol

Understanding particle size effect of metal on catalysis has great significance in scientific and industrial applications. Herein, CuZnAl catalysts with narrow Cu particle size distribution had been synthesized and investigated for syngas to ethanol. Selectivity toward to C2+OH sharply increased from 8.9% to 60.5% with the increase of Cu size from 11.8 to 38.3 nm, then it slightly increased to 68.6% when further increasing the size to 49.2 nm, which was attributed to the domination of Cu (111) facet and accompanied by the formation of Cu(111)-ZnO interface at larger Cu sizes, thereby weakened hydrogenation activity and facilitated CHx formation. The in-situ DRIFTS experiment revealed that carbon chain growth was processed by the insertion of CO*/CHO* into the CHx* and the coupling of CHx* and CO2 *. These results substantially broaden the understanding the size effect of Cu and provided guidance for design more active Cu-based catalyst for ethanol synthesis.

Dynamic behavior and alkyne insertion reactions of alkenyl- and thiolate-bridged diiron carbonyl complexes

The alkenyl- and thiolate-bridged diiron carbonyl complexes [Fe2(μ-SC6H4CR1CH)(CO)6] (R1 = H or Me), which are derived from [Fe3(CO)12] and benzothiophenes, reacted with alkynes (R2CCR3) under photoirradiation conditions to form the acyl complexes [Fe2{μ-SC6H4CR1CHCR2C(R3)CO}(CO)5]. In this reaction, an alkyne and CO are inserted into the Fe–alkenyl bond, and the bulky substituents of alkynes, including a redox active ferrocenyl group, occupy the R3 position. To elucidate the reaction pathway, the reaction of the in situ generated acetonitrile complex [Fe2(μ-SC6H4CHCH)(CO)5(NCCH3)] with ethynylbenzene was monitored by 1H NMR spectroscopy. The results demonstrated that the acetonitrile complex undergoes facile insertion of the alkyne, which is followed by CO insertion to give the corresponding acyl complex [Fe2{μ-SC6H4(CH)3C(Ph)CO}(CO)5]. The reactivity of the bridging alkenyl moiety is related to the dynamic behavior of the alkenyl-thiolate ligand (SC6H4CHCH)2- as well as the entering alkyne. Temperature dependent 31P NMR measurements of the dmpm-bridged complex [Fe2(μ-SC6H4CHCH)(μ-dmpm)(CO)4] (dmpm = bis(dimethylphosphino)methane) revealed that the activation parameters for the flip-flop motion of the alkenyl-thiolate ligand are ΔH‡ = 46.7(7) kJ mol-1 and ΔS‡ = −46(2) J mol-1 K-1.

Improving yields by switching central metal ions in porphyrazine-catalyzed oxidation of glucose into value-added organic acids with SnO2 in aqueous solution.

Photocatalysis has exhibited huge potential in selective conversion of glucose into value-added chemicals. Therefore, modulation of photocatalytic material for selective upgrading of glucose is significant. Here, we have investigated the insertion of different central metal ions, Fe, Co, Mn, and Zn, into porphyrazine loading with SnO2 for access to more efficient transformation of glucose into value-added organic acids in aqueous solution at mild reaction conditions. The best selectivity for organic acids containing glucaric acid, gluconic acid, and formic acid of 85.9% at 41.2% glucose conversion was attained by using the SnO2/CoPz composite after reacting for 3h. The effects of central metal ions on surficial potential and related possible factors have been studied. Experimental results showed that the introduction of metalloporphyrazine with different central metal ions on the surface of SnO2 has a significant effect on the separation of photogenerated charges, changing the adsorption and desorption of glucose and products on the catalyst surface. The central metal ions of cobalt and iron contributed more to the positive effects toward enhancing conversion of glucose and yields of products, and manganese and zinc contributed more to the negative effects, resulting in the poor yield of products. The differences from the central metals may attribute to the surficial potential change of the composite and the coordination effects between the metal and oxygen atom. An appropriate surficial potential environment of the photocatalyst may achieve a better interactive relationship between the catalyst and reactant, while appropriate ability of producing active species matched with adsorption and desorption abilities would gain a better yield of products. These results have provided valued ideas for designing more efficient photocatalysts in selective oxidation of glucose utilizing clean solar energy in the future.

Synthesis of MAl2O4(M = Mg, Co, Ni, Zn, Ba) Nanopowders by Liquid Impregnation of Nanofibrous Alumina

We report on a controlled synthesis of MAl2O4 (M = Mg, Co, Ni, Zn, Ba) nanopowders. The method includes three main steps: (i) growth of ultraporous nanofibrous Al2O3 (UPA) monoliths and their preliminary thermal treatment to remove the adsorbed and structural water, (ii) liquid-phase M-nitrate impregnation, and (iii) heat treatment allowing to form desirable nanocrystallites. Small crystallites with a spinel structure and mean size below 10 nm were obtained in Mg, Ni, and Zn aluminates after heat treatment at 500 °C. The results suggest formation of fully inverse MgAl2O4 spinels (inversion degree I ≈ 1) after the heat treatment at temperatures below 700 °C, followed by defect healing and formation of a normal spinel (I ∼ 0.3) at higher temperatures above the onset of the UPA bulk mass transport of ∼850 °C. This behavior is due to the interplay between cation diffusion and phase nucleation processes, in agreement with Ostwald’s rule. The formation of metastable spinel phases in agreement with Ostwald’s rule was confirmed after insertion of Co2+, Zn2+ (inverse spinel), and Ni2+ (normal spinel) cations. The insertion of Ba2+ cations into the UPA precursor resulted in the stuffed tridymite phase. The nanopowder synthesis route after upgrading to a large scale can contribute to the fabrication of functional materials for radiation-tolerant optics (M = Mg, Zn), catalysis (M = Ni, Co), nanophosphors (M = Ba), etc.

Highly Distorted Bismuth–Nickel(II) Complex

The synthesis and characterization of a series of nickel complexes bearing a bismuth-containing pincer ligand are presented herein. In particular, synthesis of a 4-coordinate Bi-Ni(II) complex allows the influence of bismuth on a d8 Ni(II) ion to be investigated. A trigonal-bipyramidal complex, (BiP2)Ni(PPh) (1), possessing an anionic bismuth donor was prepared via the Bi-C bond cleavage of a BiP3 ligand (BiP3 = Bi(o-PiPr2-C6H4)3) mediated by Ni(0). To remove a PPh moiety, compound 1 was treated with MeI to give a 5-coordinate nickel(II) complex (MeBiP2)Ni(PPh)(I) (2), followed by its exposure to heat or UV irradiation, resulting in the formation of a nickel halide complex, (BiP2)Ni(I) (3). The X-ray crystal structure of 2 revealed that the methyl moiety binds to a bismuth site, providing a neutral MeBiP2 ligand, while the iodide anion is bound to the nickel(II) center, displacing one phosphine donor. Because of the methylation on a Bi site, the Bi-Ni bond in 2 is clearly elongated relative to that of 1, which indicates that the bonding interactions between Bi and Ni are substantially different. Interestingly, compound 3 revealing a sawhorse geometry is significantly distorted away from a square-planar structure compared to the previously reported nickel(II) pincer complexes, (NP2)Ni(Cl) and (PP2)Ni(I). Such difference indicates that a bismuth donor can be a structurally influencing cooperative site for a nickel(II) ion, leading to have a Ni(I)-Bi(II) character. Migratory insertion of CO into a Ni-C bond of 1 gives (BiP2)Ni(COPPh) (4), which further leads to an analogous methylated product (MeBiP2)Ni(COPPh)(I) (5) from reaction with MeI. Due to the structural influence of a carbonyl group in each step, the total reaction time from 1 to 3 was dramatically reduced. The bimetallic cooperativity of the complexes and unusual bonding properties presented here highlight the potential of a bismuth-nickel moiety as a new type of heterobimetallic site for the design of bimetallic complexes to facilitate a variety of chemical transformations.

Accumulation of Re-complex-based Catalytic Centers in Metal–Organic Cages for Photochemical CO2 Reduction/Insertion

Metal–organic cages (MOCs) composed of trinuclear zirconium clusters, Re-complex-based catalyst-incorporated linkers (Lcat), and catalyst-free linkers (L) are synthesized using varying ratios of Lcat and L ([{Cp3Zr3(μ3-O)(μ2-OH)3}4LcatnL6−n]4+ (n = 0.0–5.0, Cp = cyclopentadienyl)). Investigating the catalytic activity of the obtained MOCs revealed that the accumulation of the Re-complex-based catalytic centers affects the photochemical CO2 reduction and CO2 insertion into phenyl vinyl sulfone. Metal-organic cages (MOCs) composed of trinuclear zirconium clusters, Re-complex-based-catalyst-incorporated linkers (Lcat), and catalyst-free linkers (L) were synthesized with various ratios of Lcat and L. The MOCs can serve as catalysts for CO2 reduction and CO2 insertion reactions, and the effect of accumulation of active sites on the photocatalytic activity of MOCs was clarified for the first time.

Boosting the Hydroformylation Activity of a Rh/CeO2 Single-Atom Catalyst by Tuning Surface Deficiencies

Controlling the interactions between atomically dispersed metal atoms and the support plays significant roles in determining the activity and selectivity of single-atom catalysts. In this report, we tuned the local coordination environment of Rh single atoms on CeO2 via calcination to construct a highly active hydroformylation catalyst. Single-atom Rh/CeO2 calcined at a high temperature exhibits more oxygen vacancies, which lead to the formation of a large amount of low-coordination Rh active species that are more active for hydroformylation. Under the optimum conditions, the best Rh/CeO2 catalyst achieved a TOF at approximately 5000 h–1 with 100% aldehyde selectivity in propylene hydroformylation to butanal. In situ FTIR spectroscopy and in situ XPS characterizations provide strong evidence that Rh on 800 °C-calcined CeO2 is easily activated to form surface HRh(CO)2 active species, favoring propylene adsorption and CO insertion. This work highlights the significance of engineering metal–support interactions in tuning the hydroformylation performance of single-atom catalysts and contributes to mechanistic insights into single-atom Rh-catalyzed hydroformylation reactions.

14- and 17-Membered Macrocycles Containing Amide, Amino, and Carbamate Groups in The Monocyclic Skeleton: An Accidental Byproduct Obtained from a Residue after Separation.

A 14-membered cyclic compound (3) containing amide, amino, and carbamate groups, which was serendipitously obtained in the oily residue after the separation of 4-benzyl-1,4,7,10-tetraazacyldododecane-2,6-dione (2a) and 4,16-dibenzyl-1,4,7,10,13,16,19,22-octaazacyclo-tetracosane-2,6,14,18-tetraone (2b), is reported. The structure of 3 is formally a CO2 insertion between positions 3 and 4 of the 12-membered ring in 2a. The CO2 insertion was confirmed in the synthesis of diethyl 2,2'-(benzylazanediyl)diacetate (1) by the reaction of benzylamine with ethyl bromoacetate using K2CO3 as the base. In addition, the selective synthesis of 3 and ethyl N-benzyl-N-((2-ethoxy-2-oxoethoxy)carbonyl)glycinate (5) and their kinetic behavior are reported. The reaction of 5 with triethylenetetramine afforded a 17-membered macrocycle (7), which was obtained in an 18% yield. Compounds 6 and 8 were prepared from 3 and 7 by introducing benzyl groups to improve their solubility in organic solvents. Titration experiments using 1H NMR showed that both 6 and 8 exhibit Li+ selectivity.

Silica-magnesium-titanium Ziegler–Natta catalysts. Part II. Properties of the active sites and fragmentation behaviour

In this work, which follows Part I that is dedicated to the precatalyst, we investigate the electronic properties and the accessibility of the Ti active sites in a highly active silica-supported Ziegler–Natta catalyst for industrial polyethylene production, applying a multi-scale, multi-technique approach. Complementary electronic spectroscopies (i.e. Ti K-edge XANES, Ti L2,3-edge NEXAFS and DR UV–Vis-NIR) reveal the coexistence of several titanium phases, whose relative amount depends on the concentration of the alkyl aluminum activator. In addition to β-TiCl3-like clusters and monomeric Ti(IV) sites, which are already present in the precatalyst, isolated Ti(III) sites and α-TiCl3-like clusters are formed in the presence of the activator. Two families of alkylated Ti(III) sites characterized by a different electron density are detected by IR spectroscopy of adsorbed CO, and two types of Ti-acyl species are formed upon CO insertion into the Ti-alkyl bond, characterized by a different extent of η2-coordination. The whole set of data suggests that TiCl3 clusters are preferentially formed at the exterior of the catalyst particles, likely as a consequence of Ti(III) mobility in the presence of strong Lewis acids, in most cases hampering the spectroscopic detection of isolated Ti(III) sites. In contrast, only monomeric Ti(III) sites are formed at the interior of the catalyst particles, characterized by a high electron density evocative of the presence of electron donors in the close proximity (e.g. aluminum alkoxide by-products). These sites are less accessible because of diffusion limitations, and only become visible by surface-sensitive spectroscopic methods (such as Ti L2,3-edge TEY-NEXAFS) upon the fragmentation of the catalyst particles.

Unveiling the complementary mechanism in the one-pot synthesis of glycerol carbonate from CO2 and glycerol

The chemical conversion of inert carbon dioxide (CO2) into high value-added chemicals is a continuing challenge. In this work, an experimental and theoretical mechanism study is presented for one-pot synthesis of glycerol carbonate (GC) from CO2, glycerol (Gly), and propylene epoxide (PO) catalyzed by 1,8-diazabicyclo[5.4.0]undec-7-enenium iodide (HDBUI) ionic liquid. 92% GC yield was obtained in the one-pot reaction through cycloaddition of CO2 with PO to produce propylene carbonate (PC), followed by transesterification of Gly with PC to yield targeted products. Density functional theory (DFT) calculations were used to unveil the HDBUI-mediated catalytic mechanism and key catalytic species. It was revealed that the HDBUI-catalyzed cycloaddition was assisted by the hydrogen bond donor Gly, the transesterification reactant, by promoting the ring-opening of PO and the insertion of CO2. By activating Gly hydroxyl group, alkaline HDBUI-bonded propan-1-ylium-2-yl carbonate, an intermediate in cycloaddition, catalyzed transesterification. The complementary mechanism of cycloaddition and transesterification in the one-pot provides a feasible method for utilizing inert CO2.

One-pot efficient fixation of low-concentration CO2 into cyclic carbonate by mesoporous pyridine-functionalized binuclear poly(ionic liquid)s

The direct conversion of low-concentration CO2 from flue gas avoids the energy-intensive purification and concentration of CO2 to implement the next utilization, making it undoubtedly a green process. However, achieving low-concentration CO2 cycloaddition with epoxide over functional poly(ionic liquid) catalysts and understanding the relevant mechanism at the molecular level is still challenging. Here, novel mesoporous pyridine-functionalized binuclear poly(ionic liquid)s (PB-PIL)s were successfully synthesized by the polymerization of DVB, basic monomers, and binuclear ionic liquid monomers, regulating the density of pyridine sites and binuclear halogen counterions to achieve the optimum balance between the active sites and pore structure of copolymerized materials. Remarkably, PB-PILs were active in the cycloaddition reaction of the low-concentration CO2 (15% CO2 + 85% N2) without any co-catalyst and gave a 95% yield of cyclic carbonate. Relied on DFT theoretical calculation, the activation degree of pyridine to CO2 and the promotion of CO2 insertion were deeply explored, providing more broad ideas for the conversion of low-concentration CO2.

Biomass catalytic pyrolysis over CaO microspheres: Relationship between the production of bio-oil components and CO2 capture

Biomass catalytic pyrolysis is a promising way for the clean and even “Carbon-Negative” utilization of biomass via the in-situ upgrading bio-oil and reducing the emissions of CO2. In this work, CaO microspheres (CaO-H) prepared via hydrothermal method were used to adsorb CO2 and catalyze the reforming of bio-oil in the pyrolysis process of rice straw (RS) simultaneously. The results showed that CaO-H had the more strong basic sites compared with commercial CaO and thus the better adsorption capacity of CO2 (∼0.5 g/g CaO) at 700 °C and the stronger effect on the generation of bio-oil components and CO2. And strong relationships presented between the formation of CO2 and the composition of bio-oil. The yield of phenols and ketones can be enhanced by 37.17% and 56.76% respectively via the addition of CaO-H at the pyrolysis temperature of 650 °C, companying with the decrease of CO2 yield by 35.13%. It is also inferred that the CO2 reforming of bio-oil and the insertion of CO in CO2 into bio-oil components was strengthened during the biomass pyrolysis over CaO-H especially at the temperature of 650 °C. The possible mechanism of biomass pyrolysis over CaO-H was also proposed.

Electrocatalytic performance of Ni-promoted Co nanoclusters supported by N-doped carbon foams for rechargeable Zn-air batteries

Ni/Co diatomic clusters supported on nitrogen-doped carbon foams are prepared via molten salt method to improve the density of surface active sites of zinc-air battery catalysts and further explore metal-modified carbon-based catalysts. The influence of Co and Ni atoms on the carbon foam structure is investigated by X-ray diffraction and high-resolution electron microscopy, and the presence of metal atoms in N-doped carbon foams is confirmed by X-ray spectroscopy. The left shift of the diffraction peak of Co doped graphitic carbon indicates an increase in the interlayer spacing and a reduced graphitization degree, while the introducton of Ni atoms promotes graphitization. For Ni–Co/NFC-2, Ni inhibits the insertion of Co in carbon layer by increasing graphitization, thus exposing more Co-active substances on the surface, which is important for improving the catalytic process of ORR and OER. According to electrochemical tests, Ni–Co co-doped carbons exhibited superior bi-functional electrocatalytic performance with oxygen reduction reaction (ORR) Eonset = 0.97 V and a Tafel slope of 49.5 mV dec−1, accompanied by oxygen evolution reaction (OER) Ej = 10 mA cm−2 = 1.46 V. Zinc-air battery (ZAB) cell, utilizing the developed material as a catalyst, exhibited a high discharge power density of 138 mW cm−2 with stable performance for up to 200 h.

New insights into the reactivity of the triscyclopentadienyl monothiolate uranium(IV) complexes: CS2 and CO2 insertion and redox properties. A DFT theoretical approach

The structural properties of a series of triscyclopentadienyl monothiolate uranium(IV) complexes [U(Cp)3(SR)] (Cp = η5–C5H5; R = Me (1), iPr (2), Ph (3), tBu (4)) as well as their reactions with CO2 or CS2 leading to their insertion into the US bond, have been investigated using relativistic Density Functional Theory (DFT) calculations. The computed activation barriers of these reactions show that insertion of CO2 into the US bond of the thiolate complexes is easier and faster than that of CS2, in agreement with the experimental observation. The study brings to light the electrostatic interactions and steric hindrance effects that play an important role in these processes. The redox behavior of the thiolate [U(Cp)3(SR)] complexes has also been investigated, permitting to find a very nice linear correlation (R2 = 0.99) between the computed electron affinities and the experimental reduction half–wave potentials E1/2. This correlation allowed to estimate the reduction potentials of [U(Cp)3(SMe)] (1) and [U(Cp)3(StBu)] (4) for which the electrochemical measurement failed. Several population analyses were carried out, among them Nalewajski–Mrozek Bond Orders (NMBO) and Hirshfeld charges Analysis (HA) allowing to rationalize the insertion reactions and redox processes and to highlight the driving role of the uranium 5f orbitals.

Mechanistic insight into the carboxylic derivatives formation from CO2 and ethylene over iron(0)-based catalyst

Since the 1980s, nickel/palladium-based catalysts have been extensively studied for the coupling reactions of CO2 and ethylene. In this study, the CO2 and ethylene coupling mediated by the iron(0)-based catalyst with a bis(dicyclohexylphosphino)ethane (dcpe) ligand was systematically investigated by means of DFT calculations. The DFT functionals were first subjected to a benchmark test in order to describe an iron-catalyzed reaction with a two-state reactivity (TSR). For the Fe/dcpe catalytic system, the formation of the five-membered iron-lactone 3 follows a stepwise route, which is easy to occur with a low energy barrier of 13.8 kcal/mol. The competing reactions by CO2 insertion and β-H elimination determine the fate of the five-membered iron-lactone 3, which may lead to the formation of three different products, including the formation of i) succinic acid, ii) iso-methylmalonic acid, and iii) acrylic acid. The calculated TOFs showed that CO2 insertion into the five-membered iron-lactone 3 is more likely to occur (1.67 h−1 for the formation of succinic acid) compared with the β-H elimination leading to iso-methylmalonic acid and acrylic acid. Interestingly, β-H elimination can be effectively facilitated by addition of the electrophiles, and a comparable TOF of 0.042 h−1 was obtained for the formation of methyl acrylate in the presence of CH3I. Unlike nickel-/palladium-catalyzed CO2 and ethylene coupling reactions, all four iron(0)-catalyzed reaction routes investigated herein showed a two-state reactivity scenario involving spin crossover between triplet and quintet PESs. This study provides a mechanistic understanding of the intriguing iron(0)-catalyzed CO2 and ethylene coupling reactions, which may shed some light on the development of green catalysts for CO2 utilization.

K–ZrO2 Interfaces Boost CO2 Hydrogenation to Higher Alcohols

Alkali metal promoters are widely used to modify active metal sites/interfaces of heterogeneous catalysts for numerous industrial processes. However, the interplay between an alkali metal and support, a crucial catalytic parameter, has been scarcely investigated in controlling the activation behaviors of intermediates and improving catalysis. Herein, we report that K–ZrO2 interfaces can boost the production of higher alcohols (HA) from CO2 hydrogenation over an amorphous ZrO2-supported K–Cu–Fe catalyst (KFeCu/a-ZrO2). In situ spectroscopy and chemisorption demonstrate that the strong interactions between K and ZrO2 induce the formation of surface Zrδ+ sites/oxygen vacancies at K–ZrO2 interfaces, thus providing plenty of nondissociative CO activation sites. The improved molecular CO adsorption capacity at the K–ZrO2 interfaces expedites the CO insertion reaction (*CHx + *CO → *CHx-CO) at Cu–Fe5C2 interfaces, thereby driving the HA synthesis reaction with nearly 4.6 times higher activity of HA in comparison to the KFeCu/SiO2 catalyst. At the optimal conditions of 320 °C, 4 MPa, and 12 L gcat–1 h–1, the KFeCu/a-ZrO2 catalyst shows the HA space time yield of 125.0 mg gcat–1 h–1, ranking the top level among the reported single-component catalysts in the literature. Most importantly, this work provides an in-depth insight into alkali promoter–support interactions for promoting catalytic performance.

Synergistic incorporation of Fe and Co into nickel boride/NiCoHydroxide nanosheets to tune voltage plateau and charge storage in supercapacitors

For designing efficient redox metal-assisted electrodes, an understanding of the inclusive role of metal ions and their influence on the electrochemical window is a prerequisite. Herein, a trimetallic boride (NiCoFe-B)/NiCoHydroxide nanosheet is employed as an integrated electrode explicitly discussing the roles of all the metal ions through electrochemical and work function studies. The UPS study and theoretical calculations highlights the reduction of work function after insertion of Co in Ni-B framework, which increases the number of active sites and enhance charge transfer kinetics, whereas Fe insertion results in an extended electrochemical window (1.35 V). In an integrated electrode, NiCoFe-B/NiCoHydroxide (NCFB), the difference in work function of Fe-B and NiCo-B results in generation of an electric field near the interface that acts as a potential barrier, further countering the external electric field and resulting in an extended potential window. Notably, a symmetric cell with the extended potential of NCFB delivers a high energy density of 45.05 Wh kg−1 at 585.52 W kg−1 and restores 86.6% of initial capacitance over 10k cycles with excellent energy delivering ability (relaxation time constant of 2.20 s). This work provides an insight into tuning the voltage plateau by varying metal ions of different work functions.

Molybdenum tailored Co0/Co2+ active pairs on a perovskite-type oxide for direct ethanol synthesis from syngas

Selective synthesis of ethanol from syngas under the Co-based catalysts is still challenging due to the hard of regulating the active site Co0 and Co2+ ratio. In this work, a series of CaTi0.9−xCoxMo0.1O3 (x = 0, 0.1–0.4) and CaTi0.7Co0.3O3 catalysts were prepared by using citric acid complexation method to promote the synthesis of ethanol. It was found that Mo species in the perovskite lattice can regulate the Co0 and Co2+ ratio through the domain-limiting effect of perovskite and the degree of Co reduction could be adjusted by changing the Co/Mo molar ratio. Among these investigated catalysts, the total selectivity of alcohols over the catalyst with the optimal Co/Mo ratio CaTi0.6Co0.3Mo0.1O3 reached 39.1%, with ethanol accounting for 74.7%, which was ascribed to the moderate and tightly bound ratio of dissociative to non-dissociative adsorption sites on the surface and the balance of CHx-CHy coupling and CO insertion.