Co-Mn Catalysts Research Articles

Preparation of silicon foam supported CoMn catalysts and their catalytic performances in higher alcohol synthesis via syngas

A series of silicon foam supported CoMn catalysts were prepared using impregnation, precipitation, and hydrothermal methods. Combining the characterization techniques such as XRD, H2-TPR, N2 physical adsorption, TEM, and XPS, the effect of different catalyst preparation methods on the catalytic performance in the synthesis of higher alcohols from syngas was investigated. It is shown that there are Co2+(Co2C) and Co0 species on the surface of the catalyst. The active sites of Co2C-Co0 on the surface of the catalyst prepared by hydrothermal method have a good synergistic effect, which is conducive to the generation of alcohols. A higher proportion of Co2C also promotes the associative adsorption and insertion of CO, resulting in the highest alcohol selectivity. Under the reaction conditions of t=260 °C, p=5.0 MPa, GHSV=4500 h–1 and H2/CO(volume ratio)=2:1, the catalyst exhibited the best reaction performances with CO conversion of 11.1%, total alcohol selectivity of 34.7%, and C2+OH selectivity of 34.5%.

Bimetallic Co-Mn catalysts for synergistic enhancement of VOC gas-sensing performance of ZnO hierarchical nanostructures.

The synergistic effect between bonding dissimilar metals is a very effective way to improve the performance of metal catalysts. In this work, we prepared a series of bimetallic co-doped ZnO hierarchical nanostructures by controlling Mn and Co contents. The gas-sensing properties of the sensors based on the bimetallic co-doped ZnO hierarchical nanostructures were studied systematically through different volatile organic compound (VOC) vapors for the temperature range from 160 to 400 °C. In the testing of normal butanol gas by the bimetallic co-doped ZnO sensor, its performance was tens of times higher than that of pure zinc oxide, and the response values to other VOCs tested were very low, which also indicates that the sensor has good selectivity. The promoted performance is attributed to the increase of adsorbed oxygen content on the surface of the sensor material due to the bimetallic synergistic enhancement effect. XPS spectra of O 1s region of the sensor show that the adsorbed oxygen content is 22.4%, which is higher than that of the pure ZnO (8.5%). The synergistic effect between bimetallic Mn and Co leads to electron enrichment on the surface of ZnO. Electron enrichment can not only promote the activation of ZnO, but also can help to improve the gas-sensing performance.

Local Electron Environment Regulation of Spinel CoMn2O4 Induced Effective Reactant Adsorption and Transformation of Lattice Oxygen for Toluene Oxidation.

In contrast to numerous studies on oxygen species, the interaction of volatile organic compounds (VOCs) with oxides is also critical to the catalytic reaction but has hardly been considered. Herein, we develop a highly efficient Pt atom doped spinel CoMn2O4 (Pt-CoMn) for oxidation of toluene at low temperature, and the toluene conversion rate increased by 18.3 times (129.7 versus 7.1 × 10-11 mol/(m2·s)) at 160 °C compared to that of CoMn2O4. Detailed characterizations and density functional theory calculations reveal that the local electron environment of the Co sites is changed after Pt doping, and the formed electron-deficient Co sites in turn strengthen the interaction with toluene. Adsorbed toluene will react with lattice oxygen in Pt-CoMn and CoMn catalysts and convert into benzoate intermediates, and the consumption rate of benzoate is closely related to the activation of gaseous oxygen. Significantly, the abundant bulk defects of Pt-CoMn help to open the reaction channel in the CoMn spinel, which acts as an oxygen pump to promote the transformation of bulk lattice oxygen into surface lattice oxygen at lower temperatures, thus accelerating the conversion rate of benzoate intermediates into CO2 and enhancing low-temperature combustion of toluene. Pt-CoMn developed here emphasizes the regulation of VOCs adsorption strength and lattice oxygen transformation processes on CoMn2O4 by adjusting the local electron environment, which will provide new guidance for the design of efficient oxide catalysts for catalytic oxidation.

CoMn catalysts derived from partial decomposed layered CoMn-MOF materials for higher alcohol synthesis from syngas

Direct and selective conversion of syngas to higher alcohols (C2+OH, HA) is highly attractive but remains challenges in improving the high catalytic performance. Herein, a series of catalysts were prepared by thermal decomposing layered-structured CoMn-MOF materials and used in the HA synthesis.Characterization results showed that the MOF framework could partially maintain after calcination at 350 °C under N2 flow, in which the Co2+ species can provide extra non-dissociative adsorption CO sties, leading to an improved alcohol selectivity. And the addition of manganese could promote the cobalt dispersion and Co2C formation. The synergistic catalysis of these active species allowed the optimal CoMn-350 catalyst to display a superior selectivity to HA, specifically the alcohol selectivity reached 57.5% and the distribution of C2+OH in total alcohols was up to 82.4 % when the CO conversion was 51.5%. The catalyst with remaining MOF framework also showed an excellent stability during 250 h reaction. This work highlights a feasible strategy for the design of highly efficient catalysts for HA synthesis via the partial decomposing MOF materials.

Study of catalytic oxidation of toluene using Cu-Mn, Co-Mn and Ni-Mn mixed oxides catalysts

The successful synthesis of AMn2O4 (A = Co, Cu, and Ni) spinels via solution combustion was achieved in less time than other methods. All catalysts with the same fuel/nitrate ratio were used to oxidize toluene, and the relationship between their properties and activities was investigated. Among all, nickel manganite exhibited the most promising activity, and by changing the fuel/nitrate ratio, it was sought to obtain the most appropriate structure for the reaction studied. Physico-chemical analysis was used to define the characteristics of the synthesized catalysts. The results showed the successful synthesis of spinels and indicated that other materials peaks (single oxide phases) exist in the catalyst structure. BET-BJH analyses reveal the mesoporous structures and, given the limitations of the equipment, were all classified as less than 10 m2/g. The SEM images evidence the influence of the urea content used. The particle size increases at higher fuel/nitrate ratios. Samples of NiMn1.67 and NiMn2.08 showed larger and denser, sparsely dispersed clusters. Simultaneously considering reactor analysis and test results, it was found that the synthesized catalyst with a fuel/nitrate ratio of 0.5 has the best performance on toluene oxidation.

Effects of alkaline-earth metals on CoMn-based catalysts for the Fischer–Tropsch synthesis to olefins

Alkaline-earth metal promoted CoMn catalysts with higher surface basicity benefit the carburization of CoMn oxides to form more Co2C nanoprisms for olefin formation, especially for long-chain olefins.

Activation of peroxymonosulfate by bimetallic CoMn oxides loaded on coal fly ash-derived SBA-15 for efficient degradation of Rhodamine B

• Mesoporous SBA-15 is successfully synthesized with coal fly ash as the silicon source. • CoMn/SBA-15 exhibits excellent performance for RhB degradation by activating PMS. • Synergistic effects of Co and Mn species are inferred. • Non-radical ( 1 O 2 ) rather than radicals (SO 4 − and OH) contributes most to the degradation. • Mechanisms of PMS activation and the degradation pathways of RhB are proposed. In this study, we successfully synthesized SBA-15 mesoporous molecular sieve with coal fly ash (CFA) as the silicon source, fabricated bimetallic CoMn catalysts with the obtained SBA-15 as the support, and evaluated their performance for activating peroxymonosulfate (PMS) to degrade the Rhodamine B (RhB) in an aqueous solution. The characterization results signified that MnCo 2 O 4 spinel was formed and uniformly dispersed on SBA-15 for the as-prepared CoMn/SBA-15. The CoMn/SBA-15/PMS system exhibited markedly higher RhB removal efficiency compared with Co/SBA-15/PMS and Mn/SBA-15/PMS under the same reaction conditions. Moreover, bimetallic CoMn/SBA-15 presented much lighter metal leaching than the monometallic catalysts. Chemical quenching tests and electron paramagnetic resonance experiments ascertained the generation of free radicals (SO 4 − and OH) and non-radical (singlet oxygen, 1 O 2 ) reactive oxygen species by PMS activation and the dominant role 1 O 2 in RhB degradation. The formed intermediate products by RhB degradation were identified with LC-MS analyses. We have also performed LC-MS analyses to determine the formed intermediate products during RhB degradation. The present results demonstrate the pronounced potential of CFA as a silicon source of molecular sieve support for preparing various heterogeneous catalysts for the PMS-based oxidation of organic pollutants in wastewater.

Hierarchical ZSM-5 Supported CoMn Catalyst for the Production of Middle Distillate from Syngas

Bifunctional catalysts using hierarchical ZSM-5 zeolite as a support have received more attention for their specific characteristic, which is in favor of producing middle distillate hydrocarbons in Fischer–Tropsch synthesis. The hierarchical structure together with the Bronsted acidity of ZSM-5 zeolites result in the secondary reaction for hydrocracking or isomerization of heavy hydrocarbons. Herein, hierarchical ZSM-5 zeolites with different acidities and mesopore volumes are synthesized by treating zeolites with TPAOH solution. The hierarchical zeolite supported CoMn catalysts are prepared by impregnation method, and all the catalysts are characterized by XRD, BET, XPS, CO/NH₃-TPD, and Py-IR. The results show that the 0.5 M TPAOH solution treated ZSM-5 (Z5-0.5M) possesses the largest mesopore volume and a proper Bronsted acidity. In addition, the Z5-0.5M supported CoMn catalyst exhibits a selectivity of jet fuel range (C₈–C₁₆) as high as 50%, which is much higher than the maximum of 41% predicted by the Anderson–Schulz–Flory model. Moreover, the effect of cobalt loading indicates that the increased cobalt loading leads to the enhancement of CO conversion and the upshift to heavier hydrocarbons.

Catalytic Reduction of Residual Oxygen for the Purification of Carbon Dioxide Streams from Pressurized Oxy-Combustors

Pressurized oxy-combustion (OC) is regarded as an energy-efficient alternative to atmospheric OC. To utilize the captured carbon dioxide (CO2) from pressurized OC for enhanced oil recovery or carbon storage in geological formations, the CO2 product stream must meet the required purity specifications. One major impurity in OC flue gases is residual O2 (e.g., 3 vol%). In this study, a catalytic approach has been investigated to remove the residual O2 through a reduction reaction with injected methane (CH4) in a reverse-flow fixed-bed (RFFB) reactor. The performance was tested for a supported copper (Cu)-based catalyst synthesized by incipient wetness impregnation and a cobalt-manganese (CoMn) oxide catalyst synthesized by a coprecipitation method. A commercial Cu-based catalyst was also studied as the reference. Experimental results revealed that under the reverse-flow operation, the temperature profiles in the reactor were symmetrical on both sides of the catalyst zone and were more homogenous than those under the conventional one-direction-flow operation. Among the tested catalysts, the CoMn catalyst was the most reactive for promoting the reduction of O2 with CH4, able to attain >95% O2 removal at 475 °C and a gas hourly space velocity (GHSV) of 18,000 h-1 with a feed gas containing 3 vol% O2. Under all experiments, the concentrations of carbon monoxide (CO) were lower than 30 ppmv in the effluent gas streams. The reaction between O2 and CH4 could be depicted by using the Mars–van Krevelen redox mechanism based on a two-step reduction–oxidation reaction pathway.

Co-Mn catalysts for H2 production via methane pyrolysis in molten salts

A promising production route for near CO2-free H2 from natural gas is methane pyrolysis in molten salts. During a screening of catalysts (containing La, Ni, Co and Mn) as particle suspensions in molten NaBr-KBr at 850 °C – 1000 °C, mixed Co-Mn catalysts were identified as being highly promising owing to their stability at pyrolysis conditions and fast kinetics. The catalysts, which contained Co-Mn nanocrystals (~8–9 ± 1 nm) that were prepared by colloidal chemistry were further tested in-depth, and their performance with varying molar Co:Mn ratios, particle sizes and temperatures were examined. The increase of the molar Co:Mn ratio from zero to two increased the CH4 conversion at 1000 °C from 4.8% to 10.4% for the smallest catalyst size range. Furthermore, we observed for all tested Co-Mn catalysts a stable performance over ca. 24 h of methane pyrolysis at 1000 °C and product selectivities for H2 near unity. While the Co-lean particles coked, the surface of the Co-rich particles remained largely carbon-free, and an increase in the Co-content was found to inhibit interactions between the support and the active phase (e.g. inhibited CoAl2O4 and MnAl2O4 formation). The rigorous procedure for the catalyst testing presented in this work enables the field to further investigate the use of catalysts for this process, and the insights gained from experiments with particle suspensions can be applied to the design of structured packings for an industrial-scale process.

One-pot hard template synthesis of mesoporous spinel nanoparticles as efficient catalysts for low temperature CO oxidation.

Co-Fe, Cu-Cr, and Co-Mnmixed oxide catalysts were prepared using a one-pot hard template synthesis method, and their catalytic performance was investigated before and after the rearrangement of the template. To evaluate the structural properties of the catalysts, various analyses were employed, including the BET, XRD, H2-TPR, FE-SEM, EDX, and X-ray digital mapping of the elements. The results indicated that the rearrangement of the catalyst structure had a profound effect on the structural and catalytic properties, so that in all three synthesized catalysts, the specific surface and the reducibility increased significantly, and the crystalline structure and morphology of the catalysts changed remarkably. The specific surface area of the CoFe, CuCr, and CoMn catalysts increased from 3.5, 1.1, and 72.9m2/g to 151.3, 52.8, and 108.0m2/g, respectively. These structural changes significantly increased the catalytic performance. The results indicated that the 100% conversion temperature of the CoMn catalyst as the optimal sample after rearrangement was reduced from 250 to 125°C. Also, the stability of the CoMn catalyst in dry and wet conditions was investigated and the results indicated that the presence of water vapor reduced the activity and stability of the catalyst. The activation energy was also calculated on Co-Mn catalyst (59.5kJ/mol) and the results confirmed that the most probable mechanism for this reaction was the MVK mechanism.

CoMn Catalysts Derived from Hydrotalcite-Like Precursors for Direct Conversion of Syngas to Fuel Range Hydrocarbons

Two different groups of CoMn catalysts derived from hydrotalcite-like precursors were prepared through the co-precipitation method, and their performance in the direct production of gasoline and jet fuel range hydrocarbons through Fischer–Tropsch (FT) synthesis was evaluated in a batch autoclave reactor at 240 °C and 7 MPa and H2/CO of 2. The physicochemical properties of the prepared catalysts were investigated and characterized using different characterization techniques. Catalyst performance was significantly affected by the catalyst preparation method. The crystalline phase of the catalyst prepared using KOH contained Co3O4 and some Co2MnO4.5 spinels, with a lower reducibility and catalytic activity than cobalt oxide. The available cobalt active sites are responsible for the chain growth, and the accessible acid sites are responsible for the cracking and isomerization. The catalysts prepared using KOH + K2CO3 mixture as a precipitant agent exhibited a high selectivity of 51–61% for gasoline (C5–C10) and 30–50% for jet fuel (C8–C16) range hydrocarbons compared with catalysts precipitated by KOH. The CoMn-HTC-III catalyst with the highest number of available acid sites showed the highest selectivity to C5–C10 hydrocarbons, which demonstrates that a high Brønsted acidity leads to the high degree of cracking of FT products. The CO conversion did not significantly change, and it was around 35–39% for all catalysts. Owing to the poor activity in the water-gas shift reaction, CO2 formation was less than 2% in all the catalysts.

Effects of alkali metal promoters on the structure–performance relationship of CoMn catalysts for Fischer–Tropsch synthesis

Alkali metal promoters are beneficial for the formation and facet-stabilization of Co2C nanoprisms for the FTO reaction.

In Situ X-ray Absorption Spectroscopy of a Synergistic Co-Mn Oxide Catalyst for the Oxygen Reduction Reaction.

Identifying the catalytically active site(s) in the oxygen reduction reaction (ORR), under real-time electrochemical conditions, is critical to the development of fuel cells and other technologies. We have employed in situ synchrotron-based X-ray absorption spectroscopy (XAS) to investigate the synergistic interaction of a Co-Mn oxide catalyst which exhibits impressive ORR activity in alkaline fuel cells. X-ray absorption near edge structure (XANES) was used to track the dynamic structural changes of Co and Mn under both steady state (constant applied potential) and nonsteady state (potentiodynamic cyclic voltammetry, CV). Under steady state conditions, both Mn and Co valences decreased at lower potentials, indicating the conversion from Mn(III,IV) and Co(III) to Mn(II,III) and Co(II), respectively. Rapid X-ray data acquisition, combined with a slow sweep rate in CV, enabled a 3 mV resolution in the applied potential, approaching a nonsteady (potentiodynamic) state. Changes in the Co and Mn valence states were simultaneous and exhibited periodic patterns that tracked the cyclic potential sweeps. To the best of our knowledge, this represents the first study, using in situ XAS, to resolve the synergistic catalytic mechanism of a bimetallic oxide. Strategies developed/described herein can provide a promising approach to unveil the reaction mechanism for other multimetallic electrocatalysts.

Fabrication of homogeneous and highly dispersed CoMn catalysts for outstanding low temperature catalytic oxidation performance

A series of homogeneous and highly dispersed CoMnOx bimetallic oxides with different ratios were prepared through pyrolysis of CoMn-MOF-71, which was applied to the catalytic oxidation of toluene.

Removal of hexanal in cooking fume by combination of storage and plasma-catalytic oxidation on alkali-modified Co-Mn solid solution

Cooking oil fumes as an important source of volatile organic compounds in metropolitan areas are poisonous to the environment and human health. In this study, the removal of hexanal (a representative of cooking fume) using “storage-plasma catalytic oxidation” at ambient conditions has been investigated. Alkali-modified Co-Mn catalysts were synthesized by coprecipitation method and further characterized by XRD, SEM, N2 adsorption–desorption, H2-TPR, O2-TPD and XPS techniques. It was clearly shown that the Na modification afforded a remarkable enhancement in the hexanal storage capacity, which is ascribed to the formation of surface hydroxyls that resulted in the chemical adsorption. Moreover, the plasma-catalytic oxidation results showed 99.4% hexanal removal and 85.7% CO2 selectivity at a GHSV of 47700 h−1. XPS results revealed that Na modification promoted the formation of more abundant Co3+, Mn3+ cations and surface adsorbed oxygen species, thus facilitated the oxidation process. In-situ FTIR results revealed that Na modification could trigger disproportionation reaction, resulting in the transformation of adsorbed hexanal into alcohol and carboxylic acid thus further speeds up the oxidation rate. This work provides a low-cost, highly efficient and energy-consuming approach for the removal of gaseous cooking fume by storage and plasma catalytic oxidation cycle at room temperature.

Morphology control of Co2C nanostructures via the reduction process for direct production of lower olefins from syngas

Fischer-Tropsch to olefins (FTO) is recognized as a surface-catalyzed structure-sensitive reaction, and the catalytic performance is strongly influenced by the morphology and exposed facets of the active phase. Here we report the effect of the reduction process on the morphology of the active phase and the catalytic performance for FTO over the CoMn catalyst. For the catalysts reduced by 10% CO-300 °C, 10% H2-300 °C and 10% H2-250 °C, Co2C nanoprisms were formed after reaching the steady state. However, for the catalysts reduced by CO-300 °C and 10% H2-400 °C, Co2C nanospheres were found instead. Both Co2C nanoprisms and nanospheres were present for the spent sample reduced by 10% H2-350 °C. Kinetic study found Co2C nanospheres to possess higher activation energy, and are more sensitive to hydrogen than Co2C nanoprisms. Density functional theory (DFT) calculations were also performed to clarify the structure-performance relationship of Co2C nanostructures for syngas conversion.

Inexpensive but Highly Efficient Co–Mn Mixed‐Oxide Catalysts for Selective Oxidation of 5‐Hydroxymethylfurfural to 2,5‐Furandicarboxylic Acid

A highly active and inexpensive Co-Mn mixed-oxide catalyst was prepared and used for selective oxidation of 5-hydroxymethylfurfural (HMF) into 2, 5-furandicarboxylic acid (FDCA). Co-Mn mixed-oxide catalysts with different Co/Mn molar ratios were prepared through a simple solid-state grinding method-a low-cost and green catalyst preparation method. The activity of these catalysts was evaluated for selective aerobic oxidation of HMF into FDCA in water. Excellent HMF conversion (99 %) and FDCA yield (95 % ) were obtained under the best reaction conditions (i.e., 120 °C, 5 h, Co-Mn mixed-oxide catalyst with a Co/Mn molar ratio of 0.25 calcined at 300 °C (Co-Mn-0.25) and 1 MPa O2 ). The catalyst could be reused five times without a significant decrease in activity. The results demonstrated that the catalytic activity and selectivity of the Co-Mn mixed-oxide catalysts prepared through solid-state grinding were superior to the same Co-Mn catalyst prepared through a conventional coprecipitation method. The high catalytic activity of the Co-Mn-0.25 catalyst was attributed to its high lattice oxygen mobility and the presence of different valence states of manganese. The high activity and low cost of the Co-Mn mixed-oxide catalysts prepared by solid-state grinding make it promising for industrial application for the manufacturing of polyethylene furanoate, a bioreplacement for polyethylene terephthalate, from sustainable bioresources.

Spinel-type cobalt-manganese oxide catalyst for degradation of Orange II using a novel heterogeneous photo-chemical catalysis system

A spinel-type Co-Mn oxide was designed and synthesized through a two-step oxidation-precipitation method at modest temperatures. The Co-Mn oxide was applied as the catalyst in the presence of NaHSO3 under visible light irradiation in order to establish the superiority of heterogeneous photo-chemical catalysis system. In the above system, the Co-Mn catalyst exhibited much better catalytic capability than that in either single photocatalysis or chemocatalysis system, implying that the Co-Mn catalyst could well combine photocatalysis and chemocatalysis to obtain the highest degradation efficiency of up to 94% within 40 min when using Orange II as the target pollutant. Recycling experiments results showed that the as-obtained catalyst has excellent stability and recyclability. Powder X-ray diffraction (XRD) analysis showed that the as-obtained Co-Mn catalyst had a cubic MnCo2O4.5 spinel structure. Because of relatively low temperature (180 ℃) synthesis, the catalyst was formed with nanoparticles (25–65 nm) and high specific surface area as confirmed by SEM and BET analyses. XPS indicated the presence of both manganese and cobalt species that serve as reactive sites for the catalytic oxidation reactions. Rational degradation mechanisms responsible for superior catalytic activity and durability were proposed based on a series of experimental results. The active species such as Mn(III), holes and sulfate and hydroxyl radicals were proposed to be responsible for the outstanding degradation results.

Characterization of CoMn catalyst by in situ X-ray absorption spectroscopy and wavelet analysis for Fischer–Tropsch to olefins reaction

Abstract Cobalt carbide has recently been reported to catalyse the FTO conversion of syngas with high selectivity for the production of lower olefins (C2–C4). Clarifying the formation process and atomic structure of cobalt carbide will help understand the catalytic mechanism of FTO. Herein, hydrogenation of carbon monoxide was investigated for cobalt carbide synthesized from CoMn catalyst, followed by X-ray diffraction, transmission electron microscopy, temperature programmed reaction and in situ X-ray absorption spectroscopy. By monitoring the evolution of cobalt carbide during syngas conversion, the wavelet transform results give evidence for the formation of the cobalt carbide and clearly demonstrate that the active site of catalysis was cobalt carbide.