Hydrogen production by methane decomposition using bimetallic Ni–Fe catalysts

The catalytic methane decomposition is the leading method for CO_x-free hydrogen and carbon nanomaterial production. In the present study, calcium-silicate based bimetallic Ni–Fe catalysts have been prepared and used to decompose the methane content of the ‘product gas’ obtained in the biomass gasification process for increasing total hydrogen production. Al₂O₃ was used as secondary support on calcium silicate based support material where Ni or Ni–Fe were doped by co-impregnation technique. The activity of catalysts was examined for diluted 6% methane-nitrogen mixture in a tubular reactor at different temperatures between 600 °C and 800 °C under atmospheric pressure, and data were collected using a quadrupole mass spectrometer. Catalysts were characterized by XRD, SEM/EDS, TEM, XPS, ICP-MS, BET, TPR, and TGA techniques. The relation between structural and textural properties of catalysts and their catalytic activity has been investigated. Even though the crystal structure of catalysts had a significant effect on the activity, a direct relation between the BET surface area and the activity was not observed. The methane conversion increased by increasing temperature up to 700 °C. The highest methane conversion has been obtained as 69% at 700 °C with F3 catalyst which has the highest Fe addition, and the addition of Fe improved the stability of catalysts. Moreover, carbon nanotubes with different diameter were formed during methane decomposition reaction, and the addition of Fe increased the formation tendency.     

Hydrogen generation from Al-Water reaction promoted by M-B/γ-Al2O3 (M = Co,Ni) catalyst

Al-water reaction promoted by catalysts is a promising hydrogen generation technology. In this work, a high-activity M-B/γ-Al₂O₃ (M = Co, Ni) catalyst is prepared by wet chemical reduction method. It is found that M-B/γ-Al₂O₃ catalyst significantly promotes the Al-water reaction and decreases the induction time. When the molar ratio of γ-Al₂O₃ to Co-M in Co–B/γ-Al₂O₃ catalyst is 1:1, the induction time is only 0.43 h. The catalytic activity of M-B/γ-Al₂O₃ is proportional to its active area. SEM analyses show that M-B particles are dispersed on γ-Al₂O₃ surface, which reduces the agglomeration of M-B and increases the active surface of M-B/γ-Al₂O₃, leading to a high catalytic activity. A possible mechanism is proposed, which shows that the dissociation of water molecules on γ-Al₂O₃ surface and the microgalvanic interaction between M-B and Al can promote the hydration process of passive oxide film on Al particle surface, speeding up the Al-water reaction.     

Hydrogen production by biomass gasification in supercritical water with bimetallic Ni-M/γAl2O3 catalysts (M = Cu, Co and Sn)

Supercritical water gasification (SCWG) of wet biomass is a very promising technology for hydrogen energy and the utilization of biomass resources. Ni-based catalysts are effective in catalyzing SCWG of original biomass and organic compounds for hydrogen production. In this paper, hydrogen production by SCWG of glucose over alumina-supported nickel catalysts modified with Cu, Co and Sn was studied. The bimetallic Ni-M (M = Cu, Co and Sn) catalysts were prepared by a co-impregnation method and tested in an autoclave reactor at 673 K with a feedstock concentration of 9.09 wt.%. XRD, XRF, N₂ adsorption/desorption, SEM and TGA were adopted to investigate the changes of chemical properties between Ni and Ni-M catalysts and the deactivation mechanism of catalysts. According to the experimental results, the hydrogen yield followed this order: Ni-Cu/γAl₂O₃ > Ni/γAl₂O₃ > Ni-Co/γAl₂O₃ > Ni-Sn/γAl₂O₃. The results show that Cu could improve the catalytic activity of Ni catalyst in reforming reaction of methane to produce hydrogen in SCWG. In addition, Cu can mitigate the sintering of alumina detected by SEM. Co was found to be an excellent promoter of Ni-based catalyst in relation to hydrogen selectivity.     

Highly stable M/NiO–MgO (M = Co,Cu and Fe) catalysts towards CO2 methanation

NiO–MgO nanocomposites are synthesized using solution combustion, sonochemical, and co-precipitation synthesis to understand the catalytic activity of CO₂ methanation. Excellent particle size distribution was noticed with the sonochemical routed synthesis method, and the CO₂ conversions are found to be better with the same synthesis protocol. Surface modifications in NiO–MgO composite were incorporated by doping M (M = Co, Fe, and Cu). The active catalysts are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to understand physical, structural properties and surface morphology of the nanocomposites. All catalysts showed excellent catalytic activity for the conversion of CO₂ to methane and selectivity towards methane to be higher than 85%. However, 2%Co/NiO–MgO showed the lowest activation energy of about 43 ± 2 kJ mol⁻¹ among other synthesized catalysts. The mechanism of CO₂ methanation was investigated with the inputs from temperature programming reduction with H₂ (H₂-TPR), and temperature programming desorption with CO₂ (CO₂-TPD) studies. Detailed reaction mechanism and kinetics are investigated for all doped catalysts. M/NiO–MgO offered excellent stability up to 50 h reaction time with high CO₂ conversions and CH₄ selectivities.     

H2 production from oxidative steam reforming of 1-propanol and propylene glycol over yttria-stabilized supported bimetallic Ni–M (M = Pt,Ru, Ir) catalysts

This paper reports hydrogen production from oxidative steam reforming of 1-propanol and propylene glycol over Ni–M/Y₂O₃–ZrO₂ (10% wt/wt Y₂O₃; M = Ir, Pt, Ru) bimetallic catalysts promoted with K. The results are compared with those obtained over the corresponding monometallic catalyst. The catalytic performance of the calcined catalysts was analyzed in the temperature range 723–773 K, adjusting the total composition of the reactants to O/C = 4 and S/C = 3.2–3.1 (molar ratios). The bimetallic catalysts showed higher hydrogen selectivity and lower selectivity of byproducts than the monometallic catalyst, especially at 723 K. Ni–Ir performed best in the oxidative steam reforming of both 1-propanol and propylene glycol. The presence of the noble metal favours the reduction of the NiO and the partial reduction of the support. The NiO crystalline phase present in the calcined catalysts was transformed to Ni° during oxidative steam reforming. The adsorption and subsequent reactivity of both 1-propanol and propylene glycol over Ni–Ir and Ni catalysts were followed by FTIR; C–C bond cleavage was found to occur at a lower temperature in propylene glycol than in 1-propanol.     

Electrocatalytic activity of crystalline Ni–Co–M (M = Cr,Mn, Cu) alloys on the oxygen evolution reaction in an alkaline environment

Ternary Ni₆₀Co₃₀M₁₀ (M = Cr, Mn, Cu) crystalline alloys have been characterized by means of microstructural and electrochemical techniques in view of their possible applications as electrocatalytic materials for oxygen evolution reaction (OER). The electrochemical efficiency of the electrodes has been studied on the basis of electrochemical data obtained from steady-state polarization and electrochemical impedance spectroscopy (EIS) techniques in 1 M NaOH solution at 298 K. The results were compared with those obtained on a Ni₆₀Co₄₀ commercial alloy. The overall experimental data indicate that alloying Ni–Co with Cr, Mn and Cu leads to an increase of electrocatalytic activity in oxygen evolution with respect to the Ni–Co alloy. High catalytic efficiencies were achieved on Ni₆₀Co₃₀Mn₁₀ and Ni₆₀Co₃₀Cr₁₀ electrodes, the latter being the best electrocatalyst for the OER.     

Hydrogen gas production with Ni,Ni–Co and Ni–Co–P electrodeposits as potential cathode catalyst by microbial electrolysis cells

The development of efficient and economical cathode, operating at ambient temperature and neutral pH is a crucial challenge for microbial electrolysis cell (MEC) to become commercialize hydrogen production technology. In the present work, eight different electrodes are prepared by the electroplating of Ni, Ni–Co and Ni–Co–P on two base metals i.e., Stainless Steel 316 and Copper separately to use as cathode in MEC. Electrodeposited cathode materials have been characterized by XRD, XPS, FESEM, EDX and linear voltammetry. The fabricated cathodes show higher corrosion stability with improved electro-catalytic performance for the hydrogen production in the MECs as compared to the bare cathodes (SS316 and Cu). Data obtained from linear voltammetry and MEC experiments show that developed cathode possess four times higher intrinsic catalytic activity in comparison to bare cathode. Electrodeposited cathodes are intensively examined in membrane-less MEC, operating under applied voltage of 0.6 V in batch mode at 30 ± 2 °C temperature, in neutral pH with acetate as substrate and activated sludge as inoculum. Ni–Co–P electrodeposit on Stainless Steel 316 cathode gives maximum hydrogen production rate of 4.2 ± 0.5 m³(H₂)m⁻³d⁻¹, columbic efficiencies 96.9 ± 2%, overall hydrogen recovery 90.3 ± 4%, overall energy efficiency 241.2 ± 5%, volumetric current density 310 ± 5 Am⁻³. The net energy recovery and COD removal are 4.25 kJ/gCOD and 61%, respectively. Prepared cathodes show stable performance for continuous 5 batch cycle operations in MEC.     

Fabrication of bimetallic Pt–M (M = Fe,Co, and Ni) nanoparticle/carbon nanotube electrocatalysts for direct methanol fuel cells

The electrochemical activities of three bimetallic Pt–M (M = Fe, Co, and Ni) catalysts in methanol oxidation have been investigated. An efficient approach including chemical oxidation of carbon nanotubes (CNTs), two-step refluxing, and subsequent hydrogen reduction was used to thoroughly disperse bimetallic nanopartilces on the oxidized CNTs. Three catalysts with a similar Pt:M atomic ratio, Pt–Fe (75:25), Pt–Co (75:25), and Pt–Ni (72:28), were prepared for the investigation of methanol oxidation. The Pt–M nanoparticles with an average size of 5–10 nm are uniform and cover the surface of CNTs. Cyclic voltammetry showed that the three pairs of catalysts were electrochemically active in the methanol oxidation. On the basis of the experimental results, the Pt–Co/CNT catalyst has better electrochemical activity, antipoisoning ability, and long-term cycleability than the other electrocatalysts, which can be justified by the bifunctional mechanism of bimetallic catalysts. The satisfactory results shed some light on how the use of Pt–Co/CNT composite could be a promising electrocatalyst for high-performance direct methanol fuel cell applications.     

Comparison of electrocatalytic activity of carbon-supported Au–M (M = Fe,Co, Ni,Cu and Zn) bimetallic nanoparticles for direct borohydride fuel cells

The Au–M (M = Fe, Co, Ni, Cu and Zn) bimetallic nanoparticles supported on the Vulcan XC-72R (Au–M/C) were synthesized by a reverse micelle method. The structures and compositions of the carbon supported Au–M catalysts were characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDS). The electrocatalytic activity of the Au–M bimetallic nanoparticles with respect to borohydride electro-oxidation for the application of fuel cell was investigated by voltammetry, chronoamperometry and chronopotentiometry. The results showed that alloying Au with 3d transition metals Fe, Co, Ni, Cu or Zn, a metal that leads to the maximum eight-electron oxidation of BH₄⁻, not only improved the electrode kinetics of BH₄⁻ oxidation but also reduced catalyst cost. Among the various investigated Au–M/C electrocatalysts, the Au–Zn, Au–Fe and Au–Cu catalysts showed no activity of NaBH₄ hydrolysis, and Au–Zn presented an attractive catalytic activity for borohydride oxidation.     

Ni–Co bimetallic MgO-based catalysts for hydrogen production via steam reforming of acetic acid from bio-oil

Acetic acid (AC) is a representative compound of bio-oil via fast pyrolysis of biomass, and can be processed for hydrogen production via steam reforming (SR). In the current work, the Ni_xCo_1−xMg₆O_7±δ (x = 0–1) bimetallic catalysts were prepared via co-precipitation and impregnation, and tested in SR of AC. The reaction results indicate that the monometallic catalysts were deactivated obviously in SR, while the Ni_0.2Co_0.8Mg₆O_7±δ bimetallic catalyst performed better in both activity and stability: not only the conversion of AC remained stable near 100%, but also the H₂ yield maintained stable near 3.1 mol-H₂/mol-AC. The results of XRD, BET, XPS, TG and TEM indicate that the high catalytic performance of the Ni_0.2Co_0.8Mg₆O_7±δ catalyst can be attributed to 1) resistance to oxidation of active metals, 2) resistance to coking, and 3) stability of structure and electronic properties.     

HER activity of MxNi1-x (M = Cr,Mo and W; x ≈ 0.2) alloy in acid and alkaline media

Reported are the synthesis and HER activity of M_xNi_1-x (M = Cr, Mo and W; x ≈ 0.2) alloy in acid and alkaline media. It was realized that doping group ⅥB element (Cr, Mo, W) in Ni metal matrix can greatly improve corresponding HER activity in both acid and alkaline electrolyte. Mo_xNi_1-x exhibits the highest HER activity among all samples in 1.0 M H₂SO₄ electrolyte, which it requires only 64 mV to reach current density of 10 mA/cm². Calculated free-energy of ΔG_H1 for M_xNi_1-x (M = Cr, Mo and W) well explained their HER activity trend in acid and it follows the order of Mo_xNi_1-x > W_xNi_1-x > Cr_xNi_1-x. In alkaline condition, their HER activities all deteriorate except Cr_xNi_1-x. HER activity of Cr_xNi_1-x in 1.0 M KOH (η_10(base) = 106 mV) surpasses that in 1.0 M H₂SO₄ (η_10(acid) = 160 mV) is quite unexpected. The DFT calculation suggesting the adsorbed OH holds the key and will alter the adsorption energy (ΔG_H1) of neighboring H atom on the surface in alkaline condition. This case study offers a good opportunity to investigate the factor to influence HER behavior of electrocatalyst in acid and alkaline media.     

Hydrogen storage properties of Mg–TM–La (TM = Ti,Fe, Ni) ternary composite powders prepared through arc plasma method

For the first time, Mg based Mg–Transition metal (TM) –La (TM = Ti, Fe, Ni) ternary composite powders were prepared directly through arc plasma evaporation of Mg–TM–La precursor mixtures followed by passivation in air. The composition, phase components, microstructure and hydrogen sorption properties of the composite powders were carefully investigated. Composition analyses revealed a reduction in TM and La contents for all powders when compared with the compositions of their precursors. It is observed that the composites are all mainly composed of ultrafine Mg covered by nano La₂O₃ introduced during passivation. Based on the Pressure–Composition–Temperature measurements, the hydrogenation enthalpies of Mg are determined to be −68.7 kJ/mol H₂ for Mg–Ti–La powder, −72.9 kJ/mol H₂ for Mg–Fe–La powder and −82.1 kJ/mol H₂ for Mg–Ni–La powder. Meantime, the hydrogen absorption kinetics can be significantly improved and the hydrogen desorption temperature can be reduced in the hydrogenated ternary Mg–TM–La composites when compared to those in the binary Mg–TM or Mg–RE composites. This is especially true for the Mg–Ni–La composite powder, which can absorb 1.5 wt% of hydrogen at 303 K after 3.5 h. Such rapid absorption kinetics at low temperatures can be attributed to the catalytic effects from both Mg₂Ni and La₂O₃. The results gathered in this study showed that simultaneous addition of 3d transition metals and 4f rare earth metals to Mg through the arc plasma method can effectively alter both the thermodynamic and kinetic properties of Mg ultrafine powders for hydrogen storage.     

Investigation of water gas-shift activity of Pt–MOx–CeO2/Al2O3 (M = K,Ni, Co) using modular artificial neural networks

The water gas shift activity of promoted Pt–CeO₂/Al₂O₃ catalysts were investigated in this work. The catalysts were prepared by incipient to wetness impregnation and tested using a microflow reaction system. It was found that K has beneficial effects under product-containing feed compositions while Co and Ni promoters worsen catalyst performance. The reaction temperature and feed H₂O/CO ratio positively affect the catalytic activity, whereas CO₂ and H₂ addition to the feed decreases CO conversion, as expected. The experimental results were also modeled using modular neural networks, at which the catalyst preparation and operational (reaction) variables were used together in the same network because they are interacting but processed differently because they are dissimilar in their form (i.e. categorical versus continuous) and their effects on catalytic activity. It was concluded that the effects of catalyst preparation and operational variables and their relative importance could be comprehended more accurately by using this approach, which may be also employed in other similar systems.     

Dehydrogenation characteristics of ammonia borane via boron-based catalysts (Co–B,Ni–B,Cu–B) under different hydrolysis conditions

In the present study, dehydrogenation characteristics of ammonia borane (NH₃BH₃) catalyzed via boron-based catalysts under different hydrolysis conditions were investigated. A series of boron-based catalysts (Co_1−x–B_x, Ni_1−x–B_x, and Cu_1−x–B_x, x: 0.25, 0.50, 0.75) were prepared by sol–gel method. Gels were calcinated at different temperatures (250 °C, 350 °C, and 450 °C) in order to obtain the boron-based catalysts. XRD characterizations revealed that Co–B, Ni–B, and Cu–B crystalline structures were formed during calcination at 450 °C. Hydrogen generation measurements were performed in order to determine the optimum composition of the boron-based catalyst. The maximum hydrogen generation rates were 7607 ml min⁻¹ gcat⁻¹, 3869 ml min⁻¹ gcat⁻¹ and 1178 ml min⁻¹ gcat⁻¹ for Co_0.75B_0.25, Ni_0.75B_0.25 and Cu_0.75B_0.25, respectively. Furthermore, the hydrolysis of NH₃BH₃ was performed at 20 °C, 40 °C, 60 °C and 80 °C under magnetic stirring (750 rpm), ultrasonic irradiation and non-stirring in order to determine how these parameters effect hydrolysis. Activation energies (E_a) were calculated by evaluation of the kinetic data. Under ultrasonic irradiation, the E_a in the presence of Co_0.75B_0.25, Ni_0.75B_0.25 and Cu_0.75B_0.25 were 40.85 kJ mol⁻¹, 43.19 kJ mol⁻¹ and 48.74 kJ mol⁻¹, respectively, which compares favorably with results reported in the literature. Thus, the catalytic activities of the boron-based catalysts were found to be Cu < Ni < Co and the best reaction condition for the catalytic hydrolysis of NH₃BH₃ was determined to be non-stirring < magnetic stirring < ultrasonic irradiation.     

Investigation of MBH4–VCl2, M = Li,Na or K

Systematic investigations of MBH₄−VCl₂, M = Li, Na, or K, 2:1 or 3:1, samples prepared by mechano-chemistry and different milling time in order to gain insight in the phase stability and search for novel borohydrides. The samples were investigated using powder X-ray diffraction and Raman spectroscopy. Subsequently, the samples were exposed to heat treatment and investigated by in-situ synchrotron radiation powder X-ray diffraction (SR-PXD). These studies reveal formation of numerous compounds during decomposition of the samples, which contrasts with previous investigations. In several cases the formed compounds were in a less well-crystalline state, which did not allow identification. One of the unidentified compounds was observed both in the LiBH₄−VCl₂ and NaBH₄−VCl₂ systems and appeared to decompose at T ∼ 190 °C and is assumed to be a new vanadium borohydride. Crystalline Li₂VCl₄ was observed, but a major fraction of the decomposition products appeared to be amorphous. The KBH₄−VCl₂ system revealed formation of well-crystalline solid solutions of K(BH₄)_1−xCl_x.     

Hydrogen production from CH4 dry reforming over bimetallic Ni–Co/Al2O3 catalyst

Bimetallic 5%Ni–10%Co/Al₂O₃ catalyst was synthesized using impregnation method and evaluated for methane dry reforming reaction at different reaction temperatures. NiO, Co₃O₄ and spinal metal aluminates, namely, CoAl₂O₄ and NiAl₂O₄ phases were formed on γ-Al₂O₃ support surface during calcination process. 5%Ni–10%Co/Al₂O₃ catalyst exhibited reasonable surface area of 86.93 m² g^?1 with small crystallite dimension of less than 10 nm suggesting that both Co₃O₄ and NiO phases were finely dispersed on the surface of support in agreement with results from scanning electron microscopy (SEM) measurement. Temperature-programmed calcination measurement indicates the complete thermal decomposition and oxidation of metal precursors, viz. Ni(NO₃)₂ and Co(NO₃)₂ to metal oxides and metal aluminates at below 700 K. Both CH₄ and CO₂ conversions were stable over a period of 4 h on-stream and attained an optimum at about 67% and 71%, respectively at 973 K whilst H₂ selectivity and yield were higher than 49%. The ratio of H₂/CO was always less than unity for all runs indicating the presence of reverse water–gas shift reaction. The activation energy for CH₄ and CO₂ consumption was computed as 55.60 and 40.25 kJ mol^?1, correspondingly. SEM micrograph of spent catalyst detected the formation of whisker-like carbon on catalyst surface whilst D and G bands characteristic for the appearance of amorphous and graphitic carbons in this order were observed on surface of used catalyst by Raman spectroscopy analysis. Additionally, the percentage of filamentous carbon was greater than that of graphitic carbon.     

A first-principles study of electronic structure and photocatalytic performance of two-dimensional van der Waals MTe2–As (M = Mo,W) heterostructures

To efficiently produce green energy and to overcome energy crises and environmental issues, photocatalytic water splitting has become the core heart of recent research. Fabricating heterostructures with type-II band alignment can enhance the photocatalytic activity. By first-principles computations, we study Mo(W)Te₂–As van der Waals (vdW) heterostructures as promising photocatalysts for overall water splitting. The bandgap, band edge position and optical properties can be modified by biaxial strain. With appropriate compressive strain of 2% and 3%, the WTe₂–As heterostructures show transition from type-I to type-II band alignment, which could slow down electron-hole pair recombination. Compared with Mo(W)Te₂ and As monolayers, the band edge of Mo(W)Te₂–As heterostructures is on favorable positions for straddling the water redox potentials. Moreover, Mo(W)Te₂–As heterostructures fascinatingly show strong absorption peaks in both visible and near ultra-violet region, making them promising candidates for overall water splitting photocatalysts.     

Superior hydrogen generation from sodium borohydride hydrolysis catalyzed by the bimetallic Co–Ru/C nanocomposite

Sodium borohydride has been widely regarded as a promising hydrogen carrier owing to its greatly hydrogen storing capability (10.8 wt%), high weight density and excellent stability in alkaline solutions. Herein, we first design and synthesize a series of bimetallic M-Ru/C nanocomposites (including Fe–Ru/C, Co–Ru/C, Ni–Ru/C and Cu–Ru/C), via simply alloying of commercial Ru/C with nonprecious metal, for superior H₂ evolution from the NaBH₄ hydrolysis. The result exhibits that H₂ generation is synergetically improved by alloying Ru/C with Co or Ni, while it is hindered by alloying Ru/C with Fe or Cu. Indeed, Co–Ru/C presents the highest efficient catalytic activity for H₂ generation, with the TOF of 117.69 mol(H₂)·mol_Ru^?1·min^?1, whereas Ru/C is only 57.08 mol(H₂)·mol_Ru^?1·min^?1. In addition, the TOF of Co–Ru/C reaches to 436.51 mol(H₂)·mol_Ru^?1·min^?1 (96.7 L(H₂)·g_Ru^?1·min^?1) in the presence of NaOH.     

Hydrogen production from ammonia decomposition using Co/γ-Al2O3 catalysts – Insights into the effect of synthetic method

Chemical hydrogen storage in molecules such as ammonia (>17 wt% H₂) have the unique potential to overcome the current storage and transport limitations of the H₂ economy. However, sustainable on-demand production of hydrogen via ammonia decomposition, requires the development of novel transition metal-based catalysts beyond the current use of highly active but expensive ruthenium to ensure economic feasibility. In this paper, we provide fundamental understanding of the effects of a range of synthetic methods of Co/γ-Al₂O₃ catalysts on the resulting ammonia decomposition activity. The main activity determining factors are collectively the reducibility of the cobalt species and their particle size. This systematic work demonstrates that decreasing the cobalt particle size enhances the ammonia decomposition catalytic activity. However, a careful balance is required between a strong metal-support interaction leading to small particle sizes (promoted by precipitation methods) and the formation of inactive cobalt aluminate species (encouraged by adsorption methods). In addition, impurities such as boron and chloride remaining from particular synthetic methods were found to have detrimental effects on the activity.