Cobalt nanoparticles supported on alumina nanofibers (Co/Al2O3): Cost effective catalytic system for the hydrolysis of methylamine borane

Amongst different amine-borane derivatives, methylamine-borane (CH₃NH₂BH₃) seems to be one of the capable aspirants in the storing of hydrogen attributable to its high hydrogen capacity, stability and aptitude to generate hydrogen through its catalytic hydrolysis reaction under ambient conditions. In this research paper, we report that cobalt nanoparticles supported on alumina nanofibers (Co/Al₂O₃) are acting as active nanocatalyst for catalytic hydrolysis of methylamine-borane. Co/Al₂O₃ nanocatalyst was fabricated by double-solvent method followed with wet-chemical reduction, and was characterized by utilizing various spectroscopic methods and imaging techniques. The results gathered from these analyses showed that the formation Al₂O₃ nanofibers supported cobalt(0) nanoparticles with a mean diameter of 3.9 ± 1.2 nm. The catalytic feat of these cobalt nanoparticles was scrutinized in the catalytic hydrolysis of methylamine-borane by considering their activity and durability performances. They achieve releasing of 3.0 equivalent of H₂ via methylamine-borane hydrolysis at room temperature (initial TOF = 297 mol H₂/mol metal × h). Along with activity the catalytic durability of Co/Al₂O₃ was also studied by carrying out recyclability tests and it was found that these supported cobalt nanoparticles have good durability during the course of the catalytic recycles so that Co/Al₂O₃ preserves almost its innate activity at 5th catalytic recycle. The studies presented here also contains kinetic investigation of Co/Al₂O₃ catalyzed methylamine borane hydrolysis depending on the temperature, cobalt and methylamine borane concentrations, which were used to define rate expression and the activation energy of the catalytic reaction.     

Hydrogen production from catalytic supercritical water reforming of glycerol with cobalt-based catalysts

Glycerol reforming under catalytic supercritical water at temperatures in the range of 723–848 K using Co catalyst deposited on various supports including ZrO₂, yttria-stabilized zirconia (YSZ), La₂O₃, γ-Al₂O₃, and α-Al₂O₃ was investigated. An increase in operating temperature promoted the continued increase in glycerol conversion; however, carbon formation causing system operation failure was observed for γ-Al₂O₃ and α-Al₂O₃ at high operating temperatures (i.e. 748–798 K). Co supported on YSZ provided the most efficient performance for hydrogen production. 10 wt.% Co loading on YSZ support was an optimum amount to enhance the reaction. The increase in glycerol conversion and reduction of the amount of liquid products were observed for lower weight hourly space velocity (WHSV), higher operating temperature or higher cobalt loading. On Co/YSZ catalyst, glycerol conversion of 0.94 and hydrogen yield of 3.72 was obtained with WHSV of 6.45 h⁻¹at 773 K.     

Ni and Co-based catalysts supported on ITQ-6 zeolite for hydrogen production by steam reforming of ethanol

Ni and Co catalysts supported on ITQ-6 zeolite have been synthesized and evaluated in the steam reforming of ethanol (SRE). Catalysts were also characterized by means of N₂ adsorption-desorption, XRD, H₂-TPR, and H₂-chemisorption. ITQ-6 containing Co (Co/ITQ-6) presented a higher conversion of ethanol and production of hydrogen than ITQ-6 containing Ni (Ni/ITQ-6). The lower size of the metallic cobalt particles shown in Co/ITQ-6 seems to be the major responsible of its higher catalytic performance. Regarding the reaction by-products (CO, CH₄, C₂H₄O and CO₂), Co/ITQ-6 showed the lowest selectivity at medium and high temperatures (773 and 873 K). At low reaction temperatures (673 K) the dehydrogenation reaction predominates in the Co/ITQ-6, what it is supported by the high concentration of acetaldehyde detected at this temperature. In the case of the Ni/ITQ-6 the main side reaction at 673 K seems to be the methanation reaction since large concentrations of methane are detected. Stability studies were also carried out showing lower deactivation of Co/ITQ-6 at large reaction times (24 h). Characterization of the exhausted catalysts after reaction showed the presence of coke in both catalysts. Nevertheless, Co/ITQ-6 presented the lowest coke deposition. In addition, Co/ITQ-6 exhibited the lowest metal sinterization, what could be also account for the lower deactivation exhibited by this sample. This fact could be related to the higher interaction between the cobalt metallic particles and the ITQ-6 support as the H₂-TPR studies demonstrate.     

Hydrogenation of carbon monoxide over cobalt nanoparticles supported on carbon nanotubes

This paper describes a catalytic reaction of hydrogen and carbon monoxide (Fischer-Tropsch synthesis (FTS)) over carbon nanotubes (CNTs) supported cobalt nanoparticles. We have investigated the effect of calcination of the catalysts on FTS performance using X-ray diffraction (XRD), H₂ chemisorption, temperature programmed reduction (TPR), temperature programmed oxidation (TPO), and transmission electron microscopy (TEM) techniques. With the increase of outer diameter of CNTs, specific surface area of the catalyst decreases while Co particle size increased accompanying with a decrease in CO conversion. The FTS performance is similar for samples calcined in N₂ or air at temperature below 550 °C. Over 550 °C, the results are much different in that the Co/CNTs can keep its activity due to the unchanged CNTs structure in N₂ while the Co/CNTs almost lose activity owing to the loss of CNTs structure and sintering of cobalt oxide clusters in air.     

Low-cost CuFeCo@MIL-101 as an efficient catalyst for catalytic hydrolysis of ammonia borane

Trimetallic nanoparticles of non-noble Cu–Fe–Co with different molar ratios were successfully immobilized in the metal-organic frameworks (MIL-101) via an easy impregnation–reduction process. XRD, TEM, XPS, ICP-MS and BET methods were used to characterize the catalyst. Comparing to their bimetallic counterparts, Cu₆Fe_0.8Co_3.2@MIL-101 demonstrates the best catalytic performance for dehydrogenation of ammonia borane by hydrolysis at 298 K Cu₆Fe_0.8Co_3.2@MIL-101 shows a total turnover frequency (TOF) value of 23.2 mol_H2 mol_catalyst⁻¹ min⁻¹ and an activation energy value of 37.1 kJ mol⁻¹. The enhancement of catalytic activity was attributed to a synergistic effect among copper, cobalt and iron nanoparticles supported on MIL-101. In addition, the catalyst still exhibits good stability and magnetic recyclability after seven cycles. The low-cost catalyst has good prospect for application in the field of hydrogen storage.     

PVP-stabilized Co–Ni nanoparticles as magnetically recyclable catalysts for hydrogen production from methanolysis of ammonia borane

Hydrogen production by hydrolysis of ammonia borane has been studied extensively, but the methanolysis has been progressing slowly, especially with non-noble metals as low cost catalyst, which is limited by complicated preparation methods or not conducive to actual application. Herein, a series of magnetically recyclable bimetallic Co–Ni nanoparticles were produced by a facile solution-phase reduction technique, using polyvinylpyrrolidone (PVP) as the stabilizing agent. The as-prepared Co–Ni alloys were amorphous and highly dispersed. Among six different PVP-stabilized Co_1-xNi_x nanoparticles (x = 0, 0.1, 0.3, 0.5, 0.7, 1) studied, the PVP-stabilized Co_0.7Ni_0.3 nanoparticles show the best catalytic performance with a TOF value of 35.3 mol_H2/(mol_catalyst·min) for hydrogen production from methanolysis of ammonia borane at 298 K, showing good synergistic effect between Co and Ni. Moreover, the catalyst can remain 91.2% initial catalytic activity after eight cycles, showing excellent stability and magnetic recyclability.     

Renewable hydrogen production by steam reforming of butanol over multiwalled carbon nanotube-supported catalysts

The conversion of bio-oxygenates into hydrogen (H₂) via catalytic steam reforming is a green approach for H₂ generation. In the present work, butanol was chosen as renewable feedstock for producing H₂. Two catalysts supported on multiwalled carbon nanotubes, Ni/CNT and Co/CNT, were synthesized by the wetness impregnation method and used for butanol reforming. Trials were performed in a fixed-bed reactor in the 623–773 K range using S/C ratio equal to 33.3 mol/mol (here, S/C denotes steam to carbon ratio). The Ni/CNT catalyst exhibited higher reforming activity. The best catalytic performance for Ni/CNT was observed at T = 773 K. At this temperature, high values of butanol conversion (87.3%) and H₂ yield (0.75 mol/mol) were observed at W/F_A0 = 16.7 g h/mol (here, W is the catalyst mass and F_A0 is the molar flow rate of butanol at the inlet). The performance of Ni/CNT catalyst for steam reforming of synthetic bio-butanol was also investigated at T = 773 K and H₂ yield of 0.65 mol/mol was achieved.     

Biogenic platinum-based bimetallic nanoparticles: Synthesis,characterization, antimicrobial activity and hydrogen evolution

In this study, platinum-based silver nanoparticles (Pt@Ag NPs) were synthesized by the green synthesis method, and their catalytic effects on hydrogen production were investigated. The characterization measurements of the synthesized NPs were performed by TEM, UV–Vis, XRD, and FTIR. According to TEM characterization results, Pt@Ag NPs had an average size of 5.431 nm. In experiments based on catalytic reactions for hydrogen production, test measurements were made at different parameters. It was observed that as the concentrations of the substrate and catalysts increased, the catalytic reaction accelerated, and the hydrogen release increased. Likewise, it was determined that hydrogen production increased with increasing temperature in different temperature experiments. The turnover frequency, entropy, activation energy, and enthalpy values are calculated as 702.38 h⁻¹, -160.5 J/mol.K, 32.48 kJ/mol, and 29.94 kJ/mol, respectively. According to the reusability test results, it was observed that the average reusability was found to be 85% after 5 cycles and it was confirmed that the NPs showed high-catalytic activity. In addition, the biological activities of Pt@Ag NPs, including antimicrobial, antioxidant and anticancer were tested. Pt@Ag NPs synthesized using Hibiscus sabdariffa (Hs) extract are thought to have the potential to be used in both biomedical and catalytic applications. The use of Pt@Ag NPs in the hydrogen production process shows great promise for green energy studies because it is environmentally friendly, non-toxic, and low cost.     

Hydrogen production by H2S decomposition over ceria supported transition metal (Co,Ni, Fe and Cu) catalysts

Hydrogen sulphide (H₂S) is one of the most poisonous and corrosive chemical substances existing in several natural and industrial gas streams, further considered as a valuable H₂ source. Hence, H₂S decomposition to H₂ is of paramount importance toward a sustainable energy future. In the present work, the catalytic decomposition of H₂S is explored in the temperature range of 550–850 °C and at atmospheric pressure, employing a series of ceria-based transition metal composites (i.e., Co, Ni, Fe, and Cu) as catalysts. Various characterization methods, involving BET, XRD, SEM, XPS and elemental analysis, were employed to reveal possible relationships between the obtained catalytic performance and catalysts physicochemical characteristics. The best activity and stability behaviour was exhibited by the 20 wt.% Co/CeO₂ catalyst, achieving H₂S conversions close to thermodynamic equilibrium. The superiority of Co/CeO₂ catalyst is mainly attributed to its in situ reduction and sulfation, toward the formation of highly active and stable phases (Co_1-xS_y and Ce₁₀S₁₄O_y) for H₂S decomposition.     

Nickel‒cobalt bimetallic catalysts prepared from hydrotalcite-like compounds for dry reforming of methane

Ni–Co/Mg(Al)O alloy catalysts with different Co/Ni molar ratios have been prepared from Ni- and Co-substituted Mg–Al hydrotalcite-like compounds (HTlcs) as precursors and tested for dry reforming of methane. The XRD characterization shows that Ni–Co–Mg–Al HTlcs are decomposed by calcination into Mg(Ni,Co,Al)O solid solution, and by reduction finely dispersed alloy particles are formed. H₂-TPR indicates a strong interaction between nickel/cobalt oxides and magnesia, and the presence of cobalt in Mg(Ni,Co,Al)O enhances the metal-support interaction. STEM-EDX analysis reveals that nickel and cobalt cations are homogeneously distributed in the HTlcs precursor and in the derived solid solution, and by reduction the resulting Ni–Co alloy particles are composition-uniform. The Ni–Co/Mg(Al)O alloy catalysts exhibit relatively high activity and stability at severe conditions, i.e., a medium temperature of 600 °C and a high space velocity of 120000 mL g^?1 h^?1. In comparison to monometallic Ni catalyst, Ni–Co alloying effectively inhibits methane decomposition and coke deposition, leading to a marked enhancement of catalytic stability. From CO₂-TPD and TPSR, it is suggested that alloying Ni with Co favors the CO₂ adsorption/activation and promotes the elimination of carbon species, thus improving the coke resistance. Furthermore, a high and stable activity with low coking is demonstrated at 750 °C. The hydrotalcite-derived Ni–Co/Mg(Al)O catalysts show better catalytic performance than many of the reported Ni–Co catalysts, which can be attributed to the formation of Ni–Co alloy with uniform composition, proper size, and strong metal-support interaction as well as the presence of basic Mg(Al)O as support.     

Highly dispersed cobalt nanoparticles onto nitrogen-doped carbon nanosheets for efficient hydrogen generation via catalytic hydrolysis of sodium borohydride

Porous carbon nanostructures are promising supports for stabilizing the highly dispersed metal nanoparticles and facilitating the mass transfer during the reaction, which are critical to achieve the high efficiency of hydrogen generation from sodium borohydride dehydrogenation. Herein, the catalytically active porous architectures are simply prepared by using 2-methylimidazole and melamine as reactive sources. The structural and compositional characterizations reveal the coexistence of metallic cobalt and N-doped carbon in porous architectures. Electron microscopy observations indicate that the synthesized products are smartly constructed from the carbon nanosheets with densely dispersed Co nanoparticles. Due to the notable structural features, the prepared Co@NC-600 sample presents the highly efficient activity for catalytic hydrolysis of NaBH₄ with a hydrogen generation rate of 2574 mL min⁻¹ g_cat⁻¹ and an activation energy of 47.6 kJ mol⁻¹. The catalytically active metallic Co and suitable support-effect of N-doped carbon are responsible for catalytic dehydrogenation.     

Recovery of flakey cobalt from aqueous Co(II) with simultaneous hydrogen production in microbial electrolysis cells

Flakey cobalt was successfully recovered from aqueous Co(II) with simultaneous hydrogen production in microbial electrolysis cells (MECs). At applied voltages of 0.3–0.5 V, the yields of 0.81 mol Co/mol COD and 1.21 ± 0.03–1.49 ± 0.11 mol H₂/mol COD were achieved while the energy efficiency relative to the electrical input was 22.5 ± 0.1–43.2 ± 0.7% (cobalt) and 170 ± 12–262 ± 7% (hydrogen), and the overall energy efficiency relative to both the electrical input and the energy of the anodic substrate averaged 9.4% (cobalt) and 62.8% (hydrogen). Cathode accumulated flakey crystals were verified as cobalt using both a scanning electron microscope capable of energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction analysis (XRD). Dominant bacteria on the anodes and known as exoelectrogens or recalcitrant substance degraders included Geobacter uraniireducens, Comamonas nitrativorans, uncultured Geobacter sp., Acidovorax caeni, Pseudorhodoferax caeni, and Diaphorobacter nitroreducens. The evidence of influence factors including applied voltage, pH, solution conductivity, temperature and type of buffer can contribute to improving understanding of and optimizing cobalt recovery with simultaneous hydrogen production in MECs.     

Novel highly efficient alumina-supported cobalt nitride catalyst for preferential CO oxidation at high temperatures

Novel alumina-supported cobalt nitride catalysts with Co loading ranging from 1 to 10 wt% prepared by NH₃-temperature-programmed reaction were investigated as potential catalysts for preferential CO oxidation (PROX) in excess H₂ at high temperatures. The formation of the Co₄N phase was confirmed by a combination of XRD and XPS, and the Co 2p binding energies of Co₄N reported previously were corrected to 798.2 ± 0.2 and 782.5 ± 0.2 eV. We observed that the catalytic activities of these nitrided Co/γ-Al₂O₃ catalysts were greatly related to their Co loadings. The nitrided 3 wt% Co/γ-Al₂O₃ catalyst showed the best PROX performance in temperature range of 200-220 °C, which was quite different from Co oxide precursor but was similar to Pt-group metals.     

Tuning catalytic performances of cobalt catalysts for clean hydrogen generation via variation of the type of carbon support and catalyst post-treatment temperature

Multi-walled carbon nanotubes, three types of activated carbons, single wall carbon nanotube and reduced graphene oxides were used to synthesize nano-sized Co catalysts for H₂ preparation via NH₃ decomposition. Catalyst samples were characterized by number of techniques such as N₂ physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopes (XPS), Transmission electron microscopy (TEM), CO chemisorption, temperature-programmed reduction (H₂-TPR) and temperature-programmed desorption (N₂-TPD). The catalytic activities of the studied catalysts for H₂ production via NH₃ decomposition were measured in a fixed-bed micro-reactor. Co catalyst supported on multi-wall carbon nanotubes has shown the highest catalytic activity. The Co particles size was significantly affected by the variation of the post-treatment temperature. The Co particles size in the range of 4.7–64.8 nm can be effectively controlled by varying post-treatment temperature between 230 and 700 °C. The maximum TOF of NH₃ decomposition was registered on cobalt catalyst post-treated at 600 °C.     

Magnetic dendritic KCC-1 nanosphere-supported cobalt composite as a separable catalyst for hydrogen generation from NaBH4 hydrolysis

The introduction of magnetism into a catalyst can greatly optimize its separation performance. In the present work, a kind of magnetically separable catalysts for promoting NaBH₄ hydrolysis have been fabricated by anchoring cobalt nanoparticles on magnetic dendritic KCC-1 nanospheres composed of magnetic Fe₃O₄ core and fibrous shell. The fabricated catalysts were characterized with various characterization methods, including absorption spectroscopy (AAS), scanning electron microscopy (SEM), high-resolution transmission electronic microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM), and Fourier transform infrared (FT-IR), etc. This kind of catalysts exhibit high catalytic activity for promoting the hydrolysis of NaBH₄ under alkaline conditions, giving a hydrogen generation rate and activation energy of 3.83 L min⁻¹ g_Co⁻¹ (30 °C) and 53.63 kJ mol⁻¹, respectively. After used for 5 cycles, the catalyst showed 36.5% catalytic activity reserved. Most importantly, the magnetism of the catalyst made it easily separated and recycled from the solution after the reaction completed. The development of this kind of catalysts could provide a promising option for catalyzing NaBH₄ hydrolysis for portable hydrogen production from.     

Unsupported cobalt nanoparticles as catalysts: Effect of preparation method on catalytic activity in CO2 methanation and ethanol steam reforming

Cobalt nanoparticles (10–50 nm) have been prepared by different procedures. Materials produced by reduction of cobalt chloride and nitrate by NaBH₄ contain B impurities as borates or borides. They are very active in ethanol steam reforming at 673–773 K with up to 85% hydrogen yield at 773 K. B-free samples obtained by thermal decomposition of Co₂(CO)₈ is slightly less selective to hydrogen, due to its activity in ethanol cracking to methane which is probably poisoned by boron impurities on the other catalysts. B-containing samples are inactive in CO₂ methanation and have weak activity in the reverse water gas shift (RWGS) reaction to CO. B-free nanoparticles have high activity in both CO₂ methanation and RWGS. However, methanation activity is reduced fast by growth of encapsulating carbon species. These particles however also show quite stable activity in RWGS to CO, attributed to CoO impurities.     

Dye-sensitized cobalt catalysts for high efficient visible light hydrogen evolution

In this work, high efficient non-noble metal cobalt cocatalysts implanted on the surface of graphene (G) by one-step photoreduction and in-situ chemical deposition methods for hydrogen evolution were reported. XRD and TEM characterizations showed that the Co and CoS_x nanoparticles were deposited on the graphene surface as Co/G and CoS_x/G composites. CoS_x/G and Co/G nanohybrids exhibited high photocatalytic activities for hydrogen evolution sensitized by Eosin Y (EY). The amounts of H₂ evolution reached 708.5 and 675.5 μmol over the EY-sensitized CoS_x/G and Co/G nanohybrids irradiated under visible light with wavelength longer than 420 nm in 3 h respectively. The apparent quantum efficiency (AQE) of 8.71% over EY-Co/G was accomplished under 520 nm illumination. The fluorescence results indicated that the lifetime of excited electron was remarkably increased. Graphene might promote the photogenerated electrons transfer from excited dye to the hydrogen evolution active sites such as Co or CoS_x, and consequently enhance photocatalytic hydrogen evolution efficiency.     

An efficient Co-N/C electrocatalyst for oxygen reduction facilely prepared by tuning cobalt species content

Transition metal and nitrogen co-doped carbon catalysts for the oxygen reduction reaction (ORR) have emerged as promising candidates to replace the expensive platinum catalysts but still remain a great challenge. Herein, a novel and efficient nitrogen-doped carbon material with metal cobalt co-dopant (Co–N/C) has been prepared by pyrolyzing porphyrin-based covalent organic polymer where Co is anchored. The optimized 10%-Co-N/C catalyst through facilely and efficiently tuning the cobalt content is carefully characterized by XRD, Raman, XPS, SEM and TEM for composition and microstructure analysis. This catalyst with only 0.56% Co exhibits an excellent ORR catalytic activity with a positive half-wave potential of 0.816 V (vs. RHE) in 0.1 M KOH solution, which is comparable to that of commercial Pt/C (20 wt%). Notably, the 10%-Co-N/C catalyst displays better electrochemical stability with only a loss of 5.1% of its initial current density in chronoamperometric measurement and also gives rise to stronger methanol tolerance than Pt/C. The good ORR catalytic behaviour for this catalyst may be attributed to the dispersion of the Co-N_X active sites via adjusting the contents of cobalt species in porous organic framework.     

Fast hydrogen generation from NaBH4 hydrolysis catalyzed by carbon aerogels supported cobalt nanoparticles

Carbon aerogels (CAs) with oxygen-rich functional groups and high surface area are synthesized by hydrothermal treatment of glucose in the presence of boric acid, and are used as the support for loading cobalt catalysts (CAs/Co). Cobalt nanoparticles distribute uniformly on the surface of ACs, creating highly dispersed catalytic active sites for hydrolysis of alkaline sodium borohydride solution. A rapid hydrogen generation rate of 11.22 L min⁻¹ g_(cobalt)⁻¹ is achieved at 25 °C by hydrolysis of 1 wt% NaBH₄ solution containing 10 wt% NaOH and 20 mg the CAs/Co catalyst with a cobalt loading of 18.71 wt%. Furthermore, various influences are systematically investigated to reveal the hydrolysis kinetics characteristics. The activation energy is found to be 38.4 kJ mol⁻¹. Furthermore, the CAs/Co catalyst can be reusable and its activity almost remains unchanged after recycling, indicating its promising applications in fuel cell.     

Hydroisomerization of n-hexane over metal oxides-loaded fibrous silica catalyst for cleaner fuel production

Fibrous silica (KCC-1) was impregnated with cobalt (Co), iron (Fe), and zinc (Zn) oxides which are denoted as Co/KCC-1, Fe/KCC-1 and Zn/KCC-1 for hydroisomerization of n-hexane. The characterization analysis revealed that the introduction of Co, Fe, and Zn into KCC-1 significantly altered the physicochemical properties of KCC-1 including reduced surface area, pore volume as well as crystallinity. Pyridine adsorbed IR showed that higher amount of the Lewis acid sites (LAS) and Brønsted acid sites (BAS) when introduced the Co, Fe, and Zn into KCC-1. Interestingly, a new band at 1610 cm⁻¹ of Zn/KCC-1, corresponds to the presence of LAS by the formation of binuclear species of Zn in the form of [ZnOZn]²⁺. The formation of [ZnOZn]²⁺ was further confirmed by the presence of a band at 350 nm and higher intensity of the binding energy at 1022.8 eV from UV-DRS and XPS analysis, respectively. From temperature-programmed reduction analysis, these binuclear species were formed at a higher temperature, which has a stronger interaction with the KCC-1. The proposed formation of [ZnOZn]²⁺ was also discussed in this work. Based on the n-hexane hydroisomerization, the Zn/KCC-1 possessed the most excellent catalytic performance amongst the catalysts owing to the existence of the binuclear species of [ZnOZn]²⁺, which acts as a new acidic center in the stabilization of generated protonic acid sites by trapping of electrons, resulting in increased isomers yield of n-hexane as well as no cracking products. Zn/KCC-1 showed the lowest activation energy compared to other catalysts within 423–673 K.