Redox Catalyst Research Articles

Oxygen vacancies enriched Ni-Co/SiO2@CeO2 redox catalyst for cycling methane partial oxidation and CO2 splitting

Redox catalysts play a vital role in the interconversion of two significant greenhouse gases, CO2 and CH4, via chemical looping methane dry reforming technology. Herein, a series of transition metals-alloyed and core–shell structured Ni-M/SiO2@CeO2 (M = Fe, Co, Cu, Mn, Zr) redox catalyst were fabricated and evaluated in a gas–solid fixed-bed reactor for cycling CH4 partial oxidation (POx) and CO2 splitting. The catalysts are composed of spherical SiO2 core and CeO2 shell, and the highly dispersed Ni alloy nanoparticles are the interlayer between core and shell. The oxygen vacancy concentration of Ni-M/SiO2@CeO2 followed the order of Co > Cu > Fe > Mn > Zr, and Ni alloying with transition metals significantly enhanced oxygen storage capacity (OSC). Ni-Co/SiO2@CeO2 catalyst with abundant oxygen vacancies and a high OSC showed the lowest temperatures of CH4 activation (610 °C) and CO2 decomposition (590 °C), thus demonstrating excellent redox reactivity. The catalyst exhibited superior activity and structural stability in the continuous CH4/CO2 redox cycles at 615 °C, achieving 87% CH4 conversion and 83% CO selectivity. The proposed catalyst shows great potential for the utilization of CH4 and CO2 in a redox mode, providing a new sight for design redox catalyst in chemical looping or related fields.

Combined Defect and Heterojunction Engineering in ZnTe/CoTe2@NC Sulfur Hosts Toward Robust Lithium–Sulfur Batteries

AbstractLithium–sulfur batteries (LSBs) are feasible candidates for the next generation of energy storage devices, but the shuttle effect of lithium polysulfides (LiPSs) and the poor electrical conductivity of sulfur and lithium sulfides limit their application. Herein, a sulfur host based on nitrogen‐doped carbon (NC) coated with small amount of a transition metal telluride (TMT) catalyst is proposed to overcome these limitations. The properties of the sulfur redox catalyst are tuned by adjusting the anion vacancy concentration and engineering a ZnTe/CoTe2 heterostructures. Theoretical calculations and experimental data demonstrate that tellurium vacancies enhance the adsorption of LiPSs, while the formed TMT/TMT and TMT/C heterostructures as well as the overall architecture of the composite simultaneously provide high Li+ diffusion and fast electron transport. As a result, v‐ZnTe/CoTe2@NC/S sulfur cathodes show excellent initial capacities up to 1608 mA h g−1 at 0.1C and stable cycling with an average capacity decay rate of 0.022% per cycle at 1C during 500 cycles. Even at a high sulfur loading of 5.4 mg cm–2, a high capacity of 1273 mA h g−1 at 0.1C is retained, and when reducing the electrolyte to 7.5 µL mg−1, v‐ZnTe/CoTe2@NC/S still maintains a capacity of 890.8 mA h g−1 after 100 cycles at 0.1C.

Progress in S–X Bond Formation by Halogen-Mediated Electrochemical Reactions

AbstractSulfur-containing compounds are very common and important heteroatom skeletons and are widely found in natural products, pharmaceuticals and bioactive compounds. Moreover, the development of synthetic routes to organosulfur compounds has attracted considerable attention due to their wide range of applications in organic chemistry, the pharmaceutical industry and in materials science. As one of most powerful, green and eco-friendly research areas, organic electrosynthesis, in contrast to conventional organic synthesis, can avoid the use of harmful stoichiometric external oxidants or reductants. Importantly, halide salts are widely used as supporting electrolytes and redox catalysts in indirect electrosynthesis to avoid the limitations imposed by high overpotentials in direct electrosynthesis. In recent years, significant progress has been made on the halogen-mediated electrosynthesis of organosulfur compounds. In this review, the scope, limitations and mechanisms of halogen-mediated electrochemical transformations of sulfur-containing compounds are presented and discussed.1 Introduction2 S–C Bond Formation2.1 Organic Thiocyanates2.2 Sulfonyl Compounds2.3 Other Sulfides3 Formation of Other S–X (X = N, O, S, P) Bonds4 Conclusion and Outlook

Application of Co-Mn-Al sheet-like metal oxide catalysts in the liquid phase conversion of toluene to benzaldehyde

The main problems of liquid-phase oxidation of methylarenes to benzaldehydes are that the catalytic reaction rate is slow, benzaldehydes are easily over-oxidized to form benzoic acids, and a large amount of solvent is required. These problems make it difficult to realize the liquid phase catalytic oxidation of methylarenes to benzaldehydes in industrial production. Here, we report the catalytic oxidation of toluene to form benzaldehyde, by using N-hydroxyphthalimide (NHPI) as the radical catalyst, sheet-like Co-Mn-Al oxides (CMA-n) as the redox catalyst, and 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) as the solvent. CMA-n/NHPI was found to be highly active in catalyzing the oxidation of toluene to benzaldehyde. The use of HFIP as the solvent prevents the over-oxidation of benzaldehyde to benzoic acid. In addition, the reaction proceeded at a high concentration of toluene. The conversion rate of toluene reached 5826 μmol g−1 h−1, and the generation rate of benzaldehyde reached 4049 μmol g−1 h−1.

Regulating lattice oxygen mobility of FeOx redox catalyst via W-doping for enhanced chemical looping oxidative dehydrogenation of ethane

The precise regulation of lattice oxygen mobility toward matched surface reaction kinetics is the key issue for rational design of chemical looing oxygen carriers. Herein, we successfully regulated lattice oxygen reactivity of FeOx redox catalyst via a W-doping strategy to realize efficient chemical looping oxidative dehydrogenation (CL-ODH) of ethane to ethylene. Specifically, the addition of W could significantly increase the binding energy of Fe-O bond, inhibiting the over-quick lattice oxygen migration toward over-oxidation. On this basis, the mild reduction of active Fe3O4 and slowly released oxygen ions involving in dehydrogenation at a matched kinetic rate could greatly prolong the active period, leading to a record high ethane processing capacity (120 ml·gcat−1·cycle−1) and productivity of ethylene (selectivity ∼83 %) during continuous dehydrogenation-regeneration cycles. This work provides a highly active CL-ODH catalyst and new insight into metal oxide redox chemistry.

Promoted oxygen release from copper-ceria interfacial sites for selective hydrogen production

The modulation of oxygen species is an effective strategy for selective H2 production with relevant chemical looping processes. This paper describes the promoted oxygen release from CuO-CeO2 redox catalysts for selective H2 production in chemical looping oxidative steam reforming of methanol (CL-OSRM). Despite the complete oxidation of methanol from CuO, the excess H2 production of CL-OSRM with respect to methanol steam reforming (MSR) increases linearly with the amount of active oxygen in CeO2 induced by the copper-ceria interaction. In situ spectroscopic characterizations and mechanistic study demonstrate that copper-ceria interfacial sites induce oxygen release from CeO2 to facilitate the partial oxidation of methoxy to formate species, which promotes the H2 production rate. This study provides an instructive strategy for the construction of redox catalysts for selective H2 production with chemical looping processes.

Lattice Oxygen Regulation of Perovskites for Chemical Looping Oxidative Dehydrogenation of Ethylbenzene to Styrene

The direct dehydrogenation process produces over 90% of global styrene. However, it is hampered by high energy consumption due to equilibrium limitation, a high steam/ethylbenzene feeding ratio, and complicated separation procedures. In this study, we propose the synthesis of a novel perovskite-structured metal oxide as the redox catalyst for chemical looping oxidative dehydrogenation (CL-ODH) of ethylbenzene into styrene. Lower ethylbenzene activation temperature and higher oxygen storage capacity contributing to high ethylbenzene conversion are achieved by Mn doping of the B site in SrFeO3−δ, and styrene yield is further enhanced by Ba doping of the A site. The optimized Sr0.8Ba0.2Fe0.2Mn0.8O3−δ catalyst exhibits favorable dehydrogenation activity but is deactivated in the first five redox cycles due to the severe carbonation and perovskite structure decomposition. The decarbonization treatment on the catalyst at 950 °C in an O2 atmosphere restores the perovskite structure and dehydrogenation activity, resulting in 85% ethylbenzene conversion and 89% styrene selectivity at 550 °C. Ethylbenzene on the catalyst undergoes full combustion via adsorbed oxygen, ODH of ethylbenzene into styrene and H2O using lattice oxygen, and direct dehydrogenation without available lattice oxygen. The proposed redox catalyst demonstrates efficient conversion of ethylbenzene into styrene, showing great potential for the energy conservation and process intensification of styrene production.

Numerical modeling of chemical looping oxidative dehydrogenation of ethane in parallel packed beds

Chemical looping oxidative dehydrogenation (CL-ODH) of ethane has the potential to be a highly efficient alternative to steam cracking for ethylene production. Accurate reactor modeling is of critical importance to efficiently scale up and optimize this new technology. This study reports a one-dimensional, heterogeneous packed bed model to simulate the CL-ODH of ethane to ethylene with a Na2MoO4-promoted CaTi0.1Mn0.9O3 redox catalyst. The overall reaction kinetics was well-described by coupling the gas-phase steam cracking of ethane with the reduction kinetics of the redox catalyst by H2 and C2H4. The impact of H2 on the formation rate of CO2 byproduct from C2H4 conversion was also thoroughly investigated to validate the applicability of the kinetic model under operational environments. The temperature variation within the different CL-ODH steps and the temperature distribution along the bed were also carefully considered. The accuracy of the model was validated by experiments conducted in a large lab-scale packed bed reactor (200 g catalyst loading), with an average deviation of 2.8% in terms of ethane conversion and ethylene yield. The model was subsequently used to optimize the operating parameters of the CL-ODH reactor, indicating that up to 63.7% single-pass C2 + olefin yield can be achieved with the current redox catalyst bed whereas further optimization of the redox catalyst to inhibit C2H4 activation can result in 69.4% single-pass C2 + yield while maintaining low CO2 selectivity.

Multifunctional Biosensing Platform Based on Nickel-Modified Laser-Induced Graphene.

Nickel plating electrolytes prepared by using a simple salt solution can achieve nickel plating on laser-induced graphene (LIG) electrodes, which greatly enhances the electrical conductivity, electrochemical properties, wear resistance, and corrosion resistance of LIG. This makes the LIG-Ni electrodes well suited for electrophysiological, strain, and electrochemical sensing applications. The investigation of the mechanical properties of the LIG-Ni sensor and the monitoring of pulse, respiration, and swallowing confirmed that the sensor can sense insignificant deformations to relatively large conformal strains of skin. Modulation of the nickel-plating process of LIG-Ni, followed by chemical modification, may allow for the introduction of glucose redox catalyst Ni2Fe(CN)6 with interestingly strong catalytic effects, which gives LIG-Ni impressive glucose-sensing properties. Additionally, the chemical modification of LIG-Ni for pH and Na+ monitoring also confirmed its strong electrochemical monitoring potential, which demonstrates application prospects in the development of multiple electrochemical sensors for sweat parameters. A more uniform LIG-Ni multi-physiological sensor preparation process provides a prerequisite for the construction of an integrated multi-physiological sensor system. The sensor was validated to have continuous monitoring performance, and its preparation process is expected to form a system for non-invasive physiological parameter signal monitoring, thus contributing to motion monitoring, disease prevention, and disease diagnosis.

Metal-promoted sulfated zirconia catalysts redox and acidic characteristics and their impact on n-butane isomerization

Metal-promoted sulfated zirconia catalysts redox and acidic characteristics and their impact on n-butane isomerization

Concerted oxygen diffusion across heterogeneous oxide interfaces for intensified propane dehydrogenation

Propane dehydrogenation (PDH) is an industrial technology for direct propylene production which has received extensive attention in recent years. Nevertheless, existing non-oxidative dehydrogenation technologies still suffer from the thermodynamic equilibrium limitations and severe coking. Here, we develop the intensified propane dehydrogenation to propylene by the chemical looping engineering on nanoscale core-shell redox catalysts. The core-shell redox catalyst combines dehydrogenation catalyst and solid oxygen carrier at one particle, preferably compose of two to three atomic layer-type vanadia coating ceria nanodomains. The highest 93.5% propylene selectivity is obtained, sustaining 43.6% propylene yield under 300 long-term dehydrogenation-oxidation cycles, which outperforms an analog of industrially relevant K-CrOx/Al2O3 catalysts and exhibits 45% energy savings in the scale-up of chemical looping scheme. Combining in situ spectroscopies, kinetics, and theoretical calculation, an intrinsically dynamic lattice oxygen “donator-acceptor” process is proposed that O2- generated from the ceria oxygen carrier is boosted to diffuse and transfer to vanadia dehydrogenation sites via a concerted hopping pathway at the interface, stabilizing surface vanadia with moderate oxygen coverage at pseudo steady state for selective dehydrogenation without significant overoxidation or cracking.

On the role of the nature and density of acid sites on mesostructured aluminosilicates dehydration catalysts for dimethyl ether production from CO2

In this work, we designed four different mesostructured acidic materials to be used as methanol dehydration catalysts for the one-pot CO2-to-DME process, in the form of physical mixtures with a Cu/ZnO/Al2O3-based commercial redox catalyst (CZA). The studied systems consist in a mesostructured γ-Al2O3 and three mesostructured aluminosilicates (namely Al-MCM-41, Al-SBA-15, and Al-SBA-16) with the same Si/Al ratio (= 15) but significantly different textural properties. The main goal of this work is to understand how the textural features can influence the acidic properties (typology, amount, strength, surface density) and, consequently, how catalytic performances can be correlated with acidic features. On this note, we found that the systems presenting both Brønsted and Lewis sites (namely the three aluminosilicates) show much better catalytic performances than γ-Al2O3, that only features Lewis sites, thus implying that Brønsted sites are more active towards methanol dehydration than Lewis sites. The three aluminosilicates, despite presenting comparable amounts of Brønsted sites, show significantly different performances in terms of selectivity to DME; particularly, Al-SBA-16, the system with the lowest surface area, proved to be the most efficient catalyst. This finding led us to infer that, besides Brønsted acidity, a high surface density of acid sites is a key factor to obtain a high dehydration activity; being methanol dehydration a bi-molecular reaction, the close proximity of two acid sites would indeed favor the kinetics of the process.

Rocking chair-like movement of ex-solved nanoparticles on the Ni-Co doped La0.6Ca0.4FeO3-δ oxygen carrier during chemical looping reforming coupled with CO2 splitting

Chemical looping reforming coupled with CO2 splitting is a promising CO2 utilization method that produces a valuable fuel. Here, we present a novel perovskite oxide with the composition of La0.6Ca0.4Fe0.95M0.05O3-δ (M = Ni, Co, Ni-Co) that functions both as an oxygen carrier and as a redox catalyst. Using a multi technique approach with HR-TEM, XRD, XAS, and Mössbauer spectroscopy, we find that alloy nanoparticles spontaneously form on the surface of Ni-Co doped carriers in a CH4 atmosphere, and as they are repeatedly exposed to CO2 and CH4 during the chemical loop, Fe atoms move back and forth between the inside (as Fe cations in the lattice) and the outside (as a part of metallic alloy) of the host scaffold. Eventually, the co-doped samples become highly reactive towards both gases and have excellent coking and redox stability, demonstrating record-level syngas yield (total ∼10 mmol/g) at 850 °C, over 50 redox cycles.

Coupling acid catalysis and selective oxidation over MoO3-Fe2O3 for chemical looping oxidative dehydrogenation of propane

Redox catalysts play a vital role in chemical looping oxidative dehydrogenation processes, which have recently been considered to be a promising prospect for propylene production. This work describes the coupling of surface acid catalysis and selective oxidation from lattice oxygen over MoO3-Fe2O3 redox catalysts for promoted propylene production. Atomically dispersed Mo species over γ-Fe2O3 introduce effective acid sites for the promotion of propane conversion. In addition, Mo could also regulate the lattice oxygen activity, which makes the oxygen species from the reduction of γ-Fe2O3 to Fe3O4 contribute to selectively oxidative dehydrogenation instead of over-oxidation in pristine γ-Fe2O3. The enhanced surface acidity, coupled with proper lattice oxygen activity, leads to a higher surface reaction rate and moderate oxygen diffusion rate. Consequently, this coupling strategy achieves a robust performance with 49% of propane conversion and 90% of propylene selectivity for at least 300 redox cycles and ultimately demonstrates a potential design strategy for more advanced redox catalysts.

CrOx/Ce1−xZrxO2 for chemical looping propane oxidative dehydrogenation: The redox interaction between CrOx and the support

Propane dehydrogenation is an attractive alternative for propylene production to petroleum-based routes. However, overcoming deactivation and toxicity of catalysts in propane direct dehydrogenation (PDH), and over oxidation in oxidative dehydrogenation (ODHP) remain challenging. Here, a chromium-based catalyst supported on a Ce-Zr solid solution is constructed for chemical looping oxidative propane dehydrogenation (CL-ODHP). A dual modulation of oxygen species by Zr doping was unraveled by characterizations and DFT calculation: the oxygen of surface CrOx was constrained while the oxygen mobility of the Ce-Zr support was promoted. Based on these properties, the interaction between surface CrOx and the support further enables an oxygen “donor–acceptor”, which potentially functions as in situ activation and regeneration of redox CrOx species as well as blockage of non-selective oxygen released from the Ce-Zr support. The optimized material (7.5Cr/Ce0.8Zr0.2O2) achieves propane conversion up to 50% and propylene yield of 31% at 600 °C, and has the lowest Cr content among previously reported Cr-based catalysts that have comparable performance. These results provide insights for the design of highly active and selective redox catalysts for chemical looping as a reaction engineering strategy for the upgrading of propane dehydrogenation processes.

Electrochemical Difunctionalization of Alkenes

AbstractThe electrochemical alkene difunctionalization reaction has become a powerful and sustainable tool for the efficient construction of vicinal difunctionalized structures in organic synthesis. Since only electrons are used as the redox agents, electrochemical alkene difunctionalization avoids the need for additional redox catalysts, metal catalysts, or chemical oxidants and does not generate chemical waste. Herein we summarize the latest contributions in the electrochemical difunctionalization of alkenes over the last 3–4 years. We discuss in detail the reaction features, scope, limitations, and mechanistic rationalizations of three categories of alkene difunctionalization methods: (1) electrochemical alkene difunctionalization terminated by nucleophiles, (2) electrochemical difunctionalization of alkenes terminated by radicals, and (3) electrochemical alkene difunctionalization terminated by functionality migration.1 Introduction2 Electrochemical Alkene Difunctionalization Terminated by Nucleophiles2.1 Sulfonylative Difunctionalization of Alkenes2.2 Sulfurizative/Sulfoxidative Difunctionalization of Alkenes2.3 Azidotetrazolation of Alkenes2.4 Trifluoromethylative Difunctionalization of Alkenes2.5 Diarylation of Alkenes3 Electrochemical Difunctionalization of Alkenes Terminated by Radicals3.1 Direct Radical-Coupling-Enabled Alkene Difunctionalization3.2 Metal-Mediated Radical Transfer Coupling Enabled Alkene Difunctionalization3.3 Metalloid-Mediated Radical Transfer Coupling Enabled Alkene Difunctionalization4 Electrochemical Alkene Difunctionalization Terminated by Functionality Migration5 Summary and Outlook

Targeting cancer lactate metabolism with synergistic combinations of synthetic catalysts and monocarboxylate transporter inhibitors

Synthetic anticancer catalysts offer potential for low-dose therapy and the targeting of biochemical pathways in novel ways. Chiral organo-osmium complexes, for example, can catalyse the asymmetric transfer hydrogenation of pyruvate, a key substrate for energy generation, in cells. However, small-molecule synthetic catalysts are readily poisoned and there is a need to optimise their activity before this occurs, or to avoid this occurring. We show that the activity of the synthetic organometallic redox catalyst [Os(p-cymene)(TsDPEN)] (1), which can reduce pyruvate to un-natural d-lactate in MCF7 breast cancer cells using formate as a hydride source, is significantly increased in combination with the monocarboxylate transporter (MCT) inhibitor AZD3965. AZD3965, a drug currently in clinical trials, also significantly lowers the intracellular level of glutathione and increases mitochondrial metabolism. These synergistic mechanisms of reductive stress induced by 1, blockade of lactate efflux, and oxidative stress induced by AZD3965 provide a strategy for low-dose combination therapy with novel mechanisms of action.Graphical abstract

Mesostructured γ-Al2O3-Based Bifunctional Catalysts for Direct Synthesis of Dimethyl Ether from CO2

In this work, we propose two bifunctional nanocomposite catalysts based on acidic mesostructured γ-Al2O3 and a Cu/ZnO/ZrO2 redox phase. γ-Al2O3 was synthesized by an Evaporation-Induced Self-Assembly (EISA) method using two different templating agents (block copolymers Pluronic P123 and F127) and subsequently functionalized with the redox phase using an impregnation method modified with a self-combustion reaction. These nanocomposite catalysts and their corresponding mesostructured supports were characterized in terms of structural, textural, and morphological features as well as their acidic properties. The bifunctional catalysts were tested for the CO2-to-DME process, and their performances were compared with a physical mixture consisting of the most promising support as a dehydration catalyst together with the most common Cu-based commercial redox catalyst (CZA). The results highlight that the most appropriate Pluronic for the synthesis of γ-Al2O3 is P123; the use of this templating agent allows us to obtain a mesostructure with a smaller pore size and a higher number of acid sites. Furthermore, the corresponding composite catalyst shows a better dispersion of the redox phase and, consequently, a higher CO2 conversion. However, the incorporation of the redox phase into the porous structure of the acidic support (chemical mixing), favoring an intimate contact between the two phases, has detrimental effects on the dehydration performances due to the coverage of the acid sites with the redox nanophase. On the other hand, the strategy involving the physical mixing of the two phases, distinctly preserving the two catalytic functions, assures better performances.

Redox MoO3/CaMnO3 catalysts for chemical-looping oxidative dehydrogenation of propane: A greener approach of propylene production

A redox catalyst with MoO3 loaded on CaMnO3 perovskite was evaluated for chemical-looping oxidative dehydrogenation (ODH) of propane to produce propylene. This approach requires less energy for the production per unit of propylene with minimum CO2 emission, which is highly desirable from an environmental perspective. H2-TPR indicates that the incorporation of MoO3 minimizes the release of surface oxygen, which is favorable for high propylene selectivity. XRD reveals the presence of active sites, while scanning SEM-EDX show uniform dispersion of deposited MoO3 on CaMnO3. XPS analysis demonstrates that MoO3 addition promotes the formation of lattice oxygen which improves the propylene selectivity. The highest propylene yield of 30.6% with a propylene selectivity of 59% was achieved at 550 ℃ with 10% MoO3/CaMnO3. The catalysts also show stable activity in successive redox cycles. The addition of MoO3 enhances propylene yield and selectivity, due to free lattice oxygen, as revealed by XPS and H2-TPR.

Solid state – Green construction of starch- beaded Fe3O4@Ag nanocomposite as superior redox catalyst

In this present work, a novel approach which had been developed for the green synthesis of starch-decorated Fe3O4 @Ag nanocomposite by using one-step grinding method. The magnetic core shell nanocomposite was designed by magnetite (Fe3O4) surrounded by the starch (maize corn), a biopolymer which act as a matrix for argentum (Ag) nanoparticles. This leads to the core shell structure starch – Fe3O4 @Ag nanocomposite (NC). The morphological and physical properties of the prepared nanocomposite was characterized by FE-SEM, HR-TEM, XPS, VSM, XRD, FT-IR and UV-Vis spectroscopic studies. The average particle size of the nanocomposite was found to be 9–11 nm. In addition, the nanocomposite gains a retentivity magnetisation of 25.50 emu/g makes the NC saveable for reusability. The nanocomposite had a greater stability for more than a month was confirmed with the help of UV-DRS and XRD analysis. The main advantage of the catalyst is temperature independent; During the conversion of benzaldehyde to benzoic acid, the product yield was achieved higher at ambient condition. Furthermore, the NC exposes the outstanding catalytic performance for reductive degradation of various carcinogenic water pollutants such as Methylene Blue (MB) and Methyl Red (MR) within 14 min and 18 min respectively. Moreover, it is also capable for reduction of 4-nitrophenol in an efficient manner. Thus, the NC holds a greater activity towards oxidation and reductive degradation reaction.