Biosynthesis of JC-La2CoO4 magnetic nanoparticles explored in catalytic and SMMs properties

We have reported the synthesis of JC-La2CoO4 magnetic nanoparticles from Jatropha Curcas L. leaf extract in aqueous medium and potential application study in catalytic & Single Molecule Magnets (SMMs). Several techniques were used to investigate the structural, morphological, and elemental composition, particle size, optical properties, catalytic and magnetic properties by XRD, FTIR, SEM, EDAX, XPS, UV-visible and squid magnetic measurement. It was found that the crystallite sizes and grain sizes of JC-La2CoO4 NPs were 11.3 ± 1 and 24.1 ± 1 nm respectively and surface morphology of the nanoparticles looks spherical shape with good surface area. The band gap of JC-La2CoO4 was found to be 4.95 eV indicates good semiconductor in nature. XPS studies shows that La and Co present in + 3 and + 2 oxidation state respectively and suggest the composition formula is La2CoO4 with satisfied all the valency of metal ions. The photocatalytic efficiency of La2CoO4 shows good result against methylene blue (MB) compared to other dyes like MO, NO, RhB in presence of sunlight with rate constant 56.73 × 10-3 min-1 and completely degraded within 115 mints. The importance of JC-La2CoO4 has magnetic properties with antiferromagnetic coupling and SMMs properties with nature.

Catalytic depolymerization of Kraft lignin to high yield alkylated-phenols over CoMo/SBA-15 catalyst in supercritical ethanol

Lignin is generally considered to be a renewable and sustainable resource of aromatic chemicals. However, the depolymerization of Kraft lignin (KL) for the production of selective phenolic monomers presents a significant challenge due to its highly recalcitrant nature. Therefore, in this work, we investigated the effect of metal sites and acid active sites on Mo/SBA-15, Co/SBA-15 and CoMo/SBA-15 catalysts in supercritical ethanol for the depolymerization of KL to produce phenolic monomers. Ethanol was used as a hydrogen donor solvent instead of using external hydrogen. Results showed that the bimetallic CoMo/SBA-15 catalyst exhibited significantly higher catalytic activity compared to the monometallic, Co/SBA-15, Mo/SBA-15 or bare SBA-15. The highest phenolic monomers yield of 27.04 wt% was achieved at 290 °C for 4 h over CoMo/SBA-15 catalyst. The inter-unit linkages such as β-O-4', β-β and α-O-4' in lignin were considerably cleaved during the catalytic depolymerization in supercritical ethanol. Meanwhile, higher functionality of carbonyl compounds was present in the non-catalytic bio-oil, while more alkylated phenols were produced over CoMo/SBA-15 catalyst. The major phenolic monomers identified in the catalytic bio-oil were 4-ethylguaiacol (9.15 wt%), 4-methylguaiacol (6.80 wt%), and 4-propylguaiacol (2.85 wt%). These findings suggest that the metal sites and abundant acid active sites of CoMo/SBA-15 had a synergistic effect toward the degradation of different linkages of lignin and production of selective phenolic monomers in bio-oils.

Synthesis of Blue Gahnite (ZnAl2O4:Co, Nd): A Cost-Effective Method for Producing Solar-Reflective Pigments for Cool Coatings

Developing strategies for the green synthesis of novel materials, such as pigments for protection from solar radiation, is a fundamental research subject in material science to mitigate the heat island effect. Within this perspective, the current study reports on the synthesis of blue pigments of ZnAl₂O₄:M (M = Co²⁺ and Co²⁺/Nd³⁺) using recycled metallic aluminum (discarded can seal) with reflective properties of Near-infrared radiation. The pigments were characterized by XRD, SEM, XPS, UV-Vis, NIR diffuse reflectance spectroscopy, and CIE-1976 L*a*b* color measurements. The wettability of the coatings containing the synthesized pigments was also evaluated. The structural characterization showed that the pigments present the Gahnite crystalline phase. Colorimetric measurements obtained by the CIEL*a*b* method show values correlated to blue pigments attributed to Co²⁺ ions in tetrahedral sites. The pigments exhibit high near-infrared solar reflectance (with R% ≥ 60%), with an enhancement of nearly 20% for the pigment-containing neodymium when applied in white paint, indicating that the prepared compounds have the potential to be energy-saving color pigments for coatings.

Influence of Cocatalysts (Ni, Co, and Cu) and Synthesis Method on the Photocatalytic Activity of Exfoliated Graphitic Carbon Nitride for Hydrogen Production

Exfoliated graphitic carbon nitride (ex-g-CN) was synthesized and loaded with non-noble metals (Ni, Cu, and Co). The synthesized catalysts were tested for hydrogen production using a 300-W Xe lamp equipped with a 395 nm cutoff filter. A noncommercial double-walled quartz-glass reactor irradiated from the side was used with a 1 g/L catalyst in 20 mL of a 10 vol% triethanolamine aqueous solution. For preliminary screening, the metal-loaded ex-g-CN was synthesized using the incipient wetness impregnation method. The highest hydrogen production was observed on the Ni-loaded ex-g-CN, which was selected to assess the impact of the synthesis method on hydrogen production. Ni-loaded ex-g-CN was synthesized using different synthesis methods: incipient wetness impregnation, colloidal deposition, and precipitation deposition. The catalysts were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption using the Brunauer-Emmett-Teller method, and transmission electron microscopy. The Ni-loaded ex-g-CN synthesized using the colloidal method performed best with a hydrogen production rate of 43.6 µmol h^-1 g^-1. By contrast, the catalysts synthesized using the impregnation and precipitation methods were less active, with 28.2 and 10.1 µmol h^-1 g^-1, respectively. The hydrogen production performance of the suspended catalyst (440 µmol m^-2 g^-1) showed to be superior to that of the corresponding immobilized catalyst (236 µmol m^-2 g^-1).

Microstructure and Corrosion Behavior of Laser Cladding FeCoNiCrBSi Based High-Entropy Alloy Coatings

High-entropy amorphous alloys designed based on the concept of multi-principal components have the comprehensive advantages of high passivation element content and amorphous structure, and are considered to be one of the promising alternative protective materials in extreme marine environments. However, based on the composition of traditional amorphous alloys, the multi-principal design significantly reduces the glass forming ability of high-entropy amorphous alloys. Based on the traditional FeCoCrNiBSi high-entropy amorphous alloy, Fe19.6Co19.6Ni19.6Cr19.6(B13.72Si5.88)19.6Y2 high-entropy amorphous alloy was designed by microalloying in this study. The traditional Fe43.6Co6Ni17.4Cr9B17.5Si1.5Nb5 iron-based amorphous alloy was selected as the comparison material. Then, spherical alloy powders were prepared by gas atomization. The amorphous nanocrystalline composite coatings were deposited on the 304 stainless steel by laser cladding technology. The microstructure of the coatings was characterized by scanning electron microscopy and X-ray diffractometer. The corrosion behavior of laser cladding coatings in 3.5 wt.% NaCl solution were investigated in detail. The results show that the Fe43.6Co6Ni17.4Cr9B17.5Si1.5Nb5 powder is composed of FCC, Laves and boride phases. Whereas the Fe19.6Co19.6Ni19.6Cr19.6(B13.72Si5.88)19.6Y2 high-entropy amorphous alloy powder is composed of FCC and boride phases. Due to the remelting and multiple heat treatments during the preparation of the laser cladding coatings, borides were precipitated in both coatings. The microstructure of the two coatings from the bonding area with the substrate to the top layer are plane grains, dendrite, equiaxed grains and amorphous phase, respectively. Fe19.6Co19.6Ni19.6Cr19.6(B13.72Si5.88)19.6Y2 high-entropy amorphous alloy coating exhibits high corrosion potential, passivation film resistance and low corrosion current density in 3.5 wt.% NaCl solution. In addition, the passivation film formed on the coating has higher Cr content and lower defect concentration, showing more excellent corrosion resistance.

Selective Conversion of Syngas to Olefins via Novel Cu-Promoted Fe/RGO and Fe-Mn/RGO Fischer-Tropsch Catalysts: Fixed-Bed Reactor vs Slurry-Bed Reactor

Fischer-Tropsch has become an indispensable choice in the gas-to-liquid conversion reactions to produce a wide range of petrochemicals using recently emerging biomass or other types of feedstock such as coal or natural gas. Herein we report the incorporation of novel Cu nanoparticles with two Fischer-Tropsch synthesis (FTS) catalytic systems, Fe/reduced graphene oxide (rGO) and Fe-Mn/rGO, to evaluate their FTS performance and olefin productivity in two types of reactors: slurry-bed reactor (SBR) and fixed-bed reactor (FBR). Four catalysts were compared and investigated, namely Fe, FeCu7, FeMn10Cu7, and FeMn16, which were highly dispersed over reduced graphene oxide nanosheets. The catalysts were first characterized by transmission electron microscopy (TEM), nitrogen physisorption, X-ray fluorescence (XRF), X-ray diffraction (XRD), and H-TPR techniques. In the SBR, Cu enhanced olefinity only when used alone in FeCu7 without Mn promotion. When used with Mn, the olefin yield was not changed, but light olefins decreased slightly at the expense of heavier olefins. In the FBR system, Cu as a reduction promoter improved the catalyst activity. It increased the olefin yield mainly due to increased activity, even if the CO2 decreased by the action of Cu promoters. The olefinity of the product was improved by Cu promotion but it did not exceed the landmark made by FeMn16 at 320 °C. The paraffinity was also enhanced by Cu promotion especially in the presence of Mn, indicating a strong synergistic effect. Cu was found to be better than Mn in enhancing the paraffin yield, while Mn is a better olefin yield enhancer. Finally, Cu promotion was found to enhance the selectivity towards light olefins C2-4. This study gives a deep insight into the effect of different highly dispersed FTS catalyst systems on the olefin hydrocarbon productivity and selectivity in two major types of FTS reactors.

Biomass derived efficient conversion of levulinic acid for sustainable production of γ-valerolactone over cobalt based catalyst

Biomass feedstocks offer very promising sustainable production of fuels and chemicals as fossil fuels generate greenhouse gases and are going to become scarce. Nevertheless, establishing value addition to biomass waste to produce commodity chemicals by combining economic and environmental performances is complex. In this context, hydrogenation of biomass based levulinic acid at normal atmospheric reaction conditions using robust cobalt supported on porous heterogeneous catalyst has been studied at 200 °C in a continuous process. The systematic investigation of Lewis acidic sites and low reaction temperature contribute to achieve 99 % conversion of levulinic acid and 80 % selectivity of γ-valerolactone.

CuCo alloy nanonets derived from CuCo2O4 spinel oxides for higher alcohols synthesis from syngas

Porous CuCo alloy nanonets were used as superior catalysts for higher alcohol synthesis from syngas. The catalyst was fabricated via structural topological transformation of CuCo2O4 spinel precursor.

CO2 Hydrogenation at Atmospheric Pressure and Low Temperature Using Plasma-Enhanced Catalysis over Supported Cobalt Oxide Catalysts

CO₂ is a promising renewable, cheap, and abundant C1 feedstock for producing valuable chemicals, such as CO and methanol. In conventional reactors, because of thermodynamic constraints, converting CO₂ to methanol requires high temperature and pressure, typically 250 °C and 20 bar. Nonthermal plasma is a better option, as it can convert CO₂ at near-ambient temperature and pressure. Adding a catalyst to such plasma setups can enhance conversion and selectivity. However, we know little about the effects of catalysts in such systems. Here, we study CO₂ hydrogenation in a dielectric barrier discharge plasma-catalysis setup under ambient conditions using MgO, γ-Al₂O₃, and a series of Co _x O _y /MgO catalysts. While all three catalyst types enhanced CO₂ conversion, Co _x O _y /MgO gave the best results, converting up to 35% of CO₂ and reaching the highest methanol yield (10%). Control experiments showed that the basic MgO support is more active than the acidic γ-Al₂O₃, and that MgO-supported cobalt oxide catalysts improve the selectivity toward methanol. The methanol yield can be tuned by changing the metal loading. Overall, our study shows the utility of plasma catalysis for CO₂ conversion under mild conditions, with the potential to reduce the energy footprint of CO₂-recycling processes.

Enhanced Electrochemical Properties and OER Performances by Cu Substitution in NiCo2O4 Spinel Structure

In order to improve the electrochemical performance of the NiCo2O4 material, Ni ions were partially substituted with Cu2+ ions having excellent reducing ability. All of the electrodes were fabricated by growing the Ni1-xCuxCo2O4 electrode spinel-structural active materials onto the graphite felt (GF). Five types of electrodes, NiCo2O4/GF, Ni0.875Cu0.125Co2O4/GF, Ni0.75Cu0.25Co2O4/GF, Ni0.625Cu0.375Co2O4/GF, and Ni0.5Cu0.5Co2O4/GF, were prepared for application to the oxygen evolution reaction (OER). As Cu2+ ions were substituted, the electrochemical performances of the NiCo2O4-based structures were improved, and eventually the OER activities were also greatly increased. In particular, the Ni0.75Cu0.25Co2O4/GF electrode exhibited the best OER activity in a 1.0 M KOH alkaline electrolyte: the cell voltage required to reach a current density of 10 mA cm-2 was only 1.74 V (η = 509 mV), and a low Tafel slope of 119 mV dec-1 was obtained. X-ray photoelectron spectroscopy (XPS) analysis of Ni1-xCuxCo2O4/GF before and after OER revealed that oxygen vacancies are formed around active metals by the insertion of Cu ions, which act as OH-adsorption sites, resulting in high OER activity. Additionally, the stability of the Ni0.75Cu0.25Co2O4/GF electrode was demonstrated through 1000th repeated OER acceleration stability tests with a high faradaic efficiency of 94.3%.

High-performance Platinum-free oxygen reduction reaction and hydrogen oxidation reaction catalyst in polymer electrolyte membrane fuel cell

The integration of polymer electrolyte membrane fuel cell (PEMFC) stack into vehicles necessitates the replacement of high-priced platinum (Pt)-based electrocatalyst, which contributes to about 45% of the cost of the stack. The implementation of high-performance and durable Pt metal-free catalyst for both oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) could significantly enable large-scale commercialization of fuel cell–powered vehicles. Towards this goal, a simple, scalable, single-step synthesis method was adopted to develop palladium-cobalt alloy supported on nitrogen-doped reduced graphene oxide (Pd₃Co/NG) nanocomposite. Rotating ring-disk electrode (RRDE) studies for the electrochemical activity towards ORR indicates that ORR proceeds via nearly four-electron mechanism. Besides, the mass activity of Pd₃Co/NG shows an enhancement of 1.6 times compared to that of Pd/NG. The full fuel cell measurements were carried out using Pd₃Co/NG at the anode, cathode in conjunction with Pt/C and simultaneously at both anode and cathode. A maximum power density of 68 mW/cm² is accomplished from the simultaneous use of Pd₃Co/NG as both anode and cathode electrocatalyst with individual loading of 0.5 mg/cm² at 60 °C without any backpressure. To the best of our knowledge, the present study is the first of its kind of a fully non-Pt based PEM full cell.

Utilizing FBR to produce olefins from CO reduction using Fe–Mn nanoparticles on reduced graphene oxide catalysts and comparing the performance with SBR

Mn was used as a promoter for Fe nanoparticles (NPs) loaded on reduced graphene oxide (rGO). The prepared catalysts were the unpromoted Fe/rGO catalysts along with two Mn promoted catalysts FeMn16 and FeMn29. These catalysts were used as Fischer–Tropsch catalysts in a Fixed Bed Reactor (FBR). The operating conditions of the reactor, namely temperature, pressure and space velocity, were varied to evaluate the catalyst performance and the olefin productivity. The olefins were produced in maximum yields of 34.5% and 31.3% with FeMn29 at 320 and 340 °C respectively. The ratio of light to heavy olefins was three times higher at 340 °C. The catalysts showed good stability up to 50 h of interrupted operation while varying the conditions at each interruption. The performance of the catalysts in the FBR was compared with a previous investigation carried out in an SBR under identical conditions with the same catalysts. The FBR was found to be more Mn tolerant than the SBR, giving very high conversion activity with high Mn concentrations (FeMn29). The FBR produced olefins in much higher yields than the SBR. The SBR was more selective to light olefins at low temperatures and high Mn loading levels, while the FBR produced light olefins at higher selectivities at high temperatures and high Mn concentrations.

Producing olefin rich products from the FTS reaction in both FBR and SBR reactors using Fe–Mn/rGO catalysts.

Mn–Fe nanoparticles on a reduced graphene oxide catalyst for enhanced olefin production from syngas in a slurry reactor

Fe nanoparticles (NPs) supported on reduced graphene oxide (rGO) nano-sheets were promoted with Mn and used for the production of light olefins in Fischer–Tropsch reactions carried out in a slurry bed reactor (SBR). The prepared catalysts were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), transmission electron microscope (TEM), Raman spectroscopy, N₂ physisorption, temperature programmed reduction (TPR) and X-ray photoelectron spectroscopic (XPS) methods. Mn was shown to preferentially migrate to the Fe NP surface, forming a Mn-rich shell encapsulating a core rich in Fe. The Mn shell regulated the diffusion of molecules to and from the catalyst core, and preserved the metallic Fe phase by lowering magnetite formation and carburization, so decreasing water gas shift reaction (WGSR) activity and CO conversion, respectively. Furthermore, the Mn shell reduced H₂ adsorption and increased CO dissociative adsorption which enhanced olefin selectivity by limiting hydrogenation reactions. Modification of the Mn shell thickness regulated the catalytic activity and olefin selectivity. Simultaneously the weak metal–support interaction further increased the migration ability owing to the utilization of a graphene-based support. Space velocities, pressures and operating temperatures were also tested in the reactor to further enhance light olefin production. A balanced Mn shell thickness produced with a Mn concentration of 16 mol Mn/100 mol Fe was found to give a good olefin yield of 19% with an olefin/paraffin (O/P) ratio of 0.77. Higher Mn concentrations shielded the active sites and reduced the conversion dramatically, causing a fall in olefin production. The optimum operating conditions were found to be 300 °C, 2 MPa and 4.2 L g⁻¹ h⁻¹ of 1 : 1 H₂ : CO syngas flow; these gave the olefin yield of 19%.

Mn acted as a promoter by forming a Mn-rich layer around a core rich in Fe. The outer layer hindered the formation of magnetite, and impeded H₂ adsorption whilst encouraging CO dissociative adsorption, which gave the perfect conditions for olefin production.

In situ investigation on Co-phase evolution and its performance for Fischer–Tropsch synthesis over Nb-promoted cobalt catalysts

The influences of Nb on the Co-phase evolution, reducibility, chemisorption, and Fischer–Tropsch synthesis performance of catalysts were in situ researched.