Mechanism of Ni-catalyzed selective CO cleavage of lignin model compound benzyl phenyl ether under mild conditions

Selective cleavage of CO bonds in benzyl phenyl ether (BPE) as a typical lignin α-O-4 ether to produce aromatics is a challenging and attractive topic. Herein, the earth-abundant first-row transition metals, such as Co, Ni and Cu were supported on activated carbon (Co/AC, Ni/AC and Cu/AC) to identify their ability for cleaving CO bond of BPE. Among these catalysts, Ni/AC exhibit highest activity for cleavage of CO bond. The reaction with BPE was carried out at pretty mild condition of 140 °C and 2 MPa H₂, which is highly selective afforded toluene and phenol as the major products with the optimum yields of 88.5 and 86.5%, respectively. Based on the test, the reaction pathways were proposed. A abundant of dissociated H· atoms on Ni(0) sites forms surface active NiH species; Ni(0) activates and facilitates cleavage of the CO bond in BPE to form benzyl (C₆H₅C·) and phenoxy radicals (C₆H₅O·); H· atoms spill from active species NiH recombined together with C₆H₅C· and C₆H₅O· forming the products of toluene and phenol, respectively.     

Effect of pyridine extraction on the pyrolysis of a perhydrous coal based on in-situ FTIR analysis

Pyridine extraction of coal can separate the small molecules from macromolecule skeleton and subsequently impacts the thermal behavior of coal. A perhydrous bituminous coal with a high content of volatile matters was extracted by pyridine under microwave irradiation with an extraction yield of 24.6% on the dry, ash free basis (daf). The thermal behavior of the raw coal, its extract and residue was investigated by thermogravimetric analysis and in-situ Fourier Transform Infrared Spectroscopy (FTIR) based on the evolution of weight loss and functional groups, respectively. Though pyridine extraction had only slight effect on TG curve of the perhydrous coal, it greatly influenced the evolution of functional groups during pyrolysis. Aromatic CH and CO was the most susceptible to pyridine extraction because the absence of extractable moieties reduced the production of radicals and the reactions between small molecules and macromolecules during pyrolysis. The interactions between extractable small molecules and non-extractable macromolecules could retard the decomposition of aromatic CC and hydroxyls. The evolution of aliphatic groups and CO was slightly impacted due to the occurrence of the abundant aliphatic side groups and bridge bonds in macromolecule structures.     

Comparative study of the poisoning effect of NaCl and Na2O on selective catalytic reduction of NO with NH3 over V2O5-WO3/TiO2 catalyst

V₂O₅-WO₃/TiO₂ catalyst has been widely used in industry. Alkali metals would cause the deactivation of V₂O₅-WO₃/TiO₂ catalyst. In this paper, the poisoning deactivation of NaCl and Na₂O on V₂O₅-WO₃/TiO₂ catalyst was compared. The properties of the catalysts were characterized by BET, XPS, H₂-TPR, NH₃-TPD and in situ DRIFTS. It was found the addition of NaCl, Na₂O affected the structure, redox properties and acid sites of V₂O₅-WO₃/TiO₂ catalyst. Na⁺ would react with VOH to form VONa⁺ destroying the structure of Brønsted sites and affect the adsorption of NH₃ on the Lewis acid to restrain the generation of V⁴⁺NH₂ to decrease the SCR activity, occupying the oxygen vacancy made a decline in chemisorbed oxygen. The poisoning effect of NaCl was stronger than that of Na₂O, even if the property of weak-chemisorption of NaCl is stronger and possessed more V⁵⁺ species. There is a reason that NaCl provided HCl and then reacted with VO₂ to form ClVOClOH to adsorb NH₃. However, ClVOClOH cannot make the catalysis selectively generate nitrogen and water.     

Low-temperature SCR of NO with NH3 over biomass char supported highly dispersed MnCe mixed oxides

Series of catalysts with MnCe mixed oxides loaded onto biomass char (BC) modified by nitric acid were prepared via impregnation method. And these catalysts were used for the selective catalytic reduction (SCR) of NO with NH₃. MnCe (7:3)/BC catalysts with loading 6% (mass ratio) MnCe oxides showed the best NO conversion ratio of 99.2% at 175 °C. The changes of the microstructure, phase composition, metal valence state and functional groups were investigated through SEM, BET, XRD, XPS and FT-IR. It showed that nitric acid modification could increase surface acidic functional groups of biomass char. And surface functional groups on BC could increase NH₃ and NO adsorption capacity. In the denitration process, oxygen was transferred from CeO₂ to Mn₂O₃, which could promote the cyclic catalytic reaction rate, then significantly enhanced the NO conversion in the MnCe/BC catalysts. Based on the experimental results and theoretical analysis, the synergetic mechanism model of surface functional groups on the surface of BC, Mn and Ce on the catalysts was set up.     

Modeling and analysis of a model solid oxide fuel cell running on low calorific value coal gases

Solid oxide fuel cell (SOFC) is a device that produces electricity directly from oxidizing a fuel. Some of the advantages are operating at high temperatures and converting various hydrocarbon fuels directly into electricity. This study investigates the parameters that influence the cell characteristics of a cathode-supported SOFC (CSSOFC) model. Numerical modeling has been performed utilizing low calorific value coal gases, generator gas, and water gas by deriving an SOFC model based on finite element method (FEM). The effects of fuel compositions, temperature, pressure, and porosity on the performance of the developed SOFC have been examined using COMSOL software. These effects are presented by polarization and power curves. A mathematical model has been developed to determine the performance of a CSSOFC with low calorific value coal gases that were obtained from Turkey/Turk coal. It is predicted that the performance of CSSOFC is higher than that of the electrolyte-supported SOFC (ES-SOFC) for all studied fuels. Besides this, the cost of the cathode supporting materials for high-performance CSSOFC is low. The performance of SOFC using water gas is higher than that of the generator gas. This being maybe the hydrogen content of the water gas is higher compared with the generator gas. Therefore, the result confirmed that low calorific value coal gases could be used in SOFCs as a source of fuel. Moreover, the power of the CSSOFC increases as the pressure, temperature, and hydrogen content increase.     

Electrodeposition of NiMoCu coatings from roasted nickel matte in deep eutectic solvent for hydrogen evolution reaction

It is attractive to design and develop a low-cost and environment friendly material preparation route for the catalysts used in alkaline hydrogen evolution reaction. Mineral reconstruction in chlorination roasting and electrodeposition in deep eutectic solvent have been combined in this work. The electrodeposition of NiMoCu coatings from roasted nickel matte precursor in choline chloride (ChCl)-urea deep eutectic solvent (DES) has been investigated. Cyclic voltammetry (CV) implies that the electrodeposition process of NiMoCu coatings in ChCl-urea DES consists of a one-step reaction of Ni(II), a two-step reaction of Cu(II) and Ni/Mo inductive co-deposition. The hydrogen evolution performance parameters of deposited NiMoCu coatings have been systematically studied in alkaline solution by linear sweep voltammetry (LSV), and the electrochemical surface area (ECSA) has been tested by CV. The hydrogen evolution kinetics of deposited NiMoCu coatings has been further investigated by electrochemical impedance spectroscopy (EIS). Owing to its high electrochemical surface area, the NiMoCu coating deposited on Ni foam at −1.2 V can deliver a current density of 10 mA cm⁻² at an overpotential of 93 mV in 1 M KOH. It is suggested that NiMoCu coating can be a promising candidate for water splitting in alkaline solution.     

Experimental and numerical study on engine fueled with different fractions of natural gas–carbon dioxide-hydrogen blends

Experimental and numerical studies on the effect of spark ignition engine fueled with different fractions of CNGCO₂H₂ blend were conducted. The results show that with the increase of CO₂ fraction, the effect of vortex on the flame wrinkle is weakened, and the flame development period increases. With the increase of the volume fraction of hydrogen in the mixture, the flame development period shortens and the flame instability trend increases. With the increase of engine speed, the turbulence intensity in the cylinder increases. The different ignition positions have great influence on the development form and combustion efficiency of the flame surface. The reasonable selection of ignition position will be beneficial to optimize and improve the performance of the whole machine.     

Electrodeposited nickel–iron–carbon–molybdenum film as efficient bifunctional electrocatalyst for overall water splitting in alkaline solution

Designing and synthesizing of efficient and inexpensive bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is one of the current research topics. In this study, NiFeCMo film in nickel mesh substrate is prepared by one-step direct-current electrodeposition method. The obtained NiFeCMo film shows the excellent electrocatalytic activity, which only requires overpotentials of 254 mV for HER and 256 mV for OER to drive current density of 10 mA cm⁻², with corresponding Tafel slopes of 163.9 and 60.3 mV·dec⁻¹ in 30% KOH medium, respectively. Moreover, NiFeCMo film only needs a low cell voltage of 1.61 V to drive current density of 10 mA cm⁻² in an alkaline electrolyzer. Such remarkably HER and OER properties of NiFeCMo alloy is attributed to the increased effective electrochemically active surface area and the synergy effect among Ni, Fe, C and Mo.     

Effect of LiCe(BH4)3Cl with a high Li ion conductivity on the hydrogen storage properties of LiMgNH system

The effect of LiCe(BH₄)₃Cl on the hydrogen storage properties of Mg(NH₂)₂2LiH system was studied systematically, which has a high Li ion conductivity. The hydrogen desorption temperatures for LiMgNH system shift to lower temperatures by 0.05LiCe(BH₄)₃Cl doping with the onset temperature of dehydrogenation decreasing by 40 °C and the peak temperature decreasing by 30 °C. The Mg(NH₂)₂2LiH–0.03LiCe(BH₄)₃Cl composite exhibits an improved comprehensive hydrogen storage properties, which can reversibly store about 5.0 wt% hydrogen at 160 °C, and released hydrogen as much as 8.6 times faster than that of the Mg(NH₂)₂2LiH composite at 160 °C. The results indicated that the LiCe(BH₄)₃Cl-containing sample exhibited much better cycling properties than that of Mg(NH₂)₂2LiH sample. XRD and FTIR results show that the structure of LiCe(BH₄)₃Cl does not change before and after hydrogen absorption/desorption, indicating it plays the catalytic effect. The hydrogen desorption activation energy of Mg(NH₂)₂2LiH doped with 0.03LiCe(BH₄)₃Cl was reduced by 37.5%. The rate-controlling step of desorption shifted from the diffusion to the chemical reaction by the addition of LiCe(BH₄)₃Cl, indicating that the diffusion rates of small ions like H⁺, Li⁺ and Mg²⁺ in LiMgNH system are significantly enhanced, which could be well explained by the improved ionic conductivity of LiCe(BH₄)₃Cl doped sample.     

First-principles study of hydrogen behavior in vanadium-based binary alloy membranes for hydrogen separation

Vanadium-based alloys are considered to be one of the most promising hydrogen separation membranes due to their high hydrogen permeability. In this study, we investigate the dissolution and diffusion behaviors of hydrogen in vanadium-based binary alloys, V₁₅M (where M = Al, Ti, Cr, Fe, Ni and Nb) alloys, using first-principles method based on density functional theory. The dissolution of hydrogen in V₁₅M alloys is affected by both the elastic and electronic properties, but the elastic effect is the main factor. The H solution energies in the alloys follow the sequence: VTi < VNb < VAl < VCr < VNi < VFe, and a smaller atom size increase the H solution energy. Therefore, the addition of alloying elements with smaller atomic sizes can reduce the solubility of hydrogen in vanadium and inhibit hydrogen embrittlement. For hydrogen diffusion, alloying elements Al, Ti and Nb can be good candidates because they have a higher diffusion coefficient. The VTi alloy has the highest hydrogen permeability, but will have serious hydrogen embrittlement due to the increased H solubility.     

Study on steam reforming of coal tar over NiCo/ceramic foam catalyst for hydrogen production: Effect of Ni/Co ratio

The effect of Ni/Co ratio on the catalytic performance of NiCo/ceramic foam catalyst for hydrogen production by steam reforming of real coal tar was studied. The NiCo/ceramic foam catalyst was synthesized by deposition-precipitation (DP) method and characterized with different methods. The experiments were conducted in a two-stage fixed-bed reactor. The results showed that the reducibility of the metallic oxides in bimetallic NiCo/ceramic foam catalysts was influenced obviously by the Ni/Co ratio.Both gas and hydrogen yield increased first and then decreased with the decline of Ni/Co ratio, and the highest hydrogen yield of 31.46 mmol g^?1 was obtained when the Ni/Co ratio was 5/5. The lowest coke deposition of 0.34 wt% was generated at the same Ni/Co ratio. The lifetime test showed the catalyst maintained catalytic activity after 14 cycles (28 h), indicating the coal tar steam reforming on NiCo/ceramic foam catalyst is a promising method for hydrogen production.     

Improved hydrogen storage properties of MgH2 with Ni-based compounds

The nanoscaled Ni-based compounds (Ni₃C, Ni₃N, NiO and Ni₂P) are synthesized by chemical methods. The MgH₂-X (X = Ni₃C, Ni₃N, NiO and Ni₂P) composites are prepared by mechanical ball-milling. The dehydrogenation properties of Mg-based composites are systematically studied using isothermal dehydrogenation apparatus, temperature-programmed desorption system and differential scanning calorimetry. It is experimentally confirmed that the dehydrogenation performance of the Mg-based materials ranks as following: MgH₂Ni₃C, MgH₂Ni₃N, MgH₂NiO and MgH₂Ni₂P. The onset dehydrogenation temperatures of MgH₂Ni₃C, MgH₂Ni₃N, MgH₂NiO and MgH₂Ni₂P are 160 °C, 180 °C, 205 °C and 248 °C, respectively. The four Mg-based composites respectively release 6.2, 4.9, 4.1 and 3.5 wt% H₂ within 20 min at 300 °C. The activation energies of MgH₂Ni₃C, MgH₂Ni₃N, MgH₂NiO and MgH₂Ni₂P are 97.8, 100.0, 119.7 and 132.5 kJ mol^?1, respectively. It' found that the MgH₂Ni₃C composites exhibit the best hydrogen storage properties. Moreover, the catalytic mechanism of the Ni-based compounds is also discussed. It is found that Ni binding with low electron-negativity element is favorable for the dehydrogenation of the Mg-based composites.     

Dry reforming of methane for hydrogen production over NiCo catalysts: Effect of NbZr promoters

Ni/Al₂O₃, NiCo/Al₂O₃MgO and NiCo/Al₂O₃MgO/NbZr nanocatalysts were prepared by the sol-gel technique with citric acid and tested in the dry reforming of methane (DRM). In this paper, the effects of Nb and Zr addition as promoters in Al₂O₃MgO supported catalysts on the physicochemical characteristics and the reaction performance in the DRM were investigated. The NbZr promoters are expected to enhance the activity and performance of the catalyst due to its high thermal stability and also improvement in the metal dispersion of the catalyst. The catalysts samples were characterized by FESEM, BET, XRD, TEM, H₂-TPR and CO₂-TPD techniques. FESEM results demonstrated that NiCo/Al₂O₃MgO/NbZr has more uniform and well-dispersion of metal than NiCo/Al₂O₃MgO. The BET results unravel that the addition of NbZr promoters increase the surface area of the synthesized catalyst due to the high surface area of the promoters. There is a formation of MgAl₂O₄ spinel-type solid solution proved by the XRD and CO₂-TPD analysis due to the interaction between alumina lattice and magnesium metal which has high resistance to carbon formation. The DRM reaction is performed in the tubular furnace reactor at 1073.15 K, 1 atm and a CH₄/CO₂ ratio of unity. The sol-gelled NiCo/Al₂O₃MgO/NbZr was found to be the most proper choice for DRM which illustrates much higher conversion (86.96% for CH₄ conversion and 87.84% for CO₂ conversion) compared to the other catalysts. This is due to the strong interaction between active metals and supports, resistance to coke formation and higher stability in DRM reaction.     

Trimetallic nanoparticles: Synthesis,characterization and catalytic degradation of formic acid for hydrogen generation

PdAgFe, FePdAg and FeAgPd trimetallic nanoparticles were synthesized by seedless and step-wise simultaneous chemical reduction of Fe³⁺, Ag⁺ and Pd²⁺ by using hydrazine in presence of cetyltrimethylammonium bromide and used as a catalyst for the degradation of formic acid. The effects of nanoparticle composition, presence of sodium format (promoter), [catalyst], [formic acid] and temperature play key roles in the hydrogen generation. The Ba(OH)₂ trap experiment and water displacement technique were used to determine the generation of CO₂ and H₂, respectively. The decomposition of formic acid followed complex-order kinetics with respect to [formic acid]. It was found that FeAgPd showed a maximum catalytic activity (turn over frequency) of 75 mol H₂ per mol catalyst per h. The activation energy (E_a = 51.6 kJ/mol), activation enthalpy (ΔH = 48.9 kJ/mol) and activation entropy (ΔS = −151.0 JK^-1 mol⁻¹) were determined and discussed for the catalytic reaction. The reusability of the FeAgPd at 50 °C shows an efficient degree of activity for six consecutive catalytic cycles.     

One-pot synthesis of PdZnO/C by microwave sintering method as an efficient electro catalyst for ethanol oxidation reaction

The PdZnO/C catalytic material for ethanol oxidation reaction is prepared by microwave heating-glycol reduction method. PdZnO is well polymerized and dispersed on XC72. The results demonstrate that PdZnO/C has better electro catalytic activity and stability for ethanol oxidation reaction than Pd/C at room temperature. ZnO/C shows no catalysis for ethanol oxidation. The oxidation peak potential of PdZnO/C electrode is shifted negatively to 0.21 V. The current density of PdZnO/C electrode is 145 mA cm⁻², while that of the Pd/C electrode is 60 mA cm⁻². Moreover, single cell discharge test shows that discharge voltage of the PdZnO/C electrode reaches to 0.41 V at 30 mA cm⁻². In summary, ZnO as a co-catalyst significantly improves the activity of PdZnO/C catalyst for ethanol oxidation reaction.     

Dimensionally stable NiFe@Co/Ti nanoporous electrodes by reactive deposition for water electrolysis

The development of efficient and dimensionally stable electrode plates is of a significant challenge for the oxygen evolution reaction in the industrial water electrolysis process. In this work, structurally stable electrode plates are developed based on the nanostructured NiFe catalysts on highly porous and dimensionally stable Co reactive deposited on Ti substrates, NiFe@Co/Ti. SEM analysis shows the hierarchically structured micro- and nano-porous structure of the Co electrode on Ti substrates by reactive deposition route. The surface area of the reactive deposited Co is 3 times larger than that of the conventional electrodeposited Co electrode, providing highly porous and stable base for the subsequent deposition of NiFe electrocatalysts. The as-prepared NiFe@Co/Ti electrode exhibits high catalytic activity towards oxygen evolution in alkaline solutions, achieving an onset potential of as low as 1.44 V (η = 210 mV) and delivering a current of 10 mA cm^?2 at an overpotential of 0.26 V. Most importantly, the electrode shows excellent stability with negligible degradation under the discharge current density at 100 mA cm^?2 for 100 h, demonstrating the practical applicability of the NiFe@Co/Ti nanostructured electrodes for industrial scale water electrolysis.     

Different modified multi-walled carbon nanotube–based anodes to improve the performance of microbial fuel cells

To clearly illustrate the activity effect of multi-walled carbon nanotubes (MWCNTs) and their functionality on anodic exoelectrogen in microbial fuel cells (MFCs), the growth of E. coli and anode biofilm on MWCNT-, MWCNTCOOH and MWCNTNH₂ modified anodes were compared with a bare carbon cloth anode. The activity effect was characterized by the amount of colony-forming units (CFUs), activity biomass, morphology of biofilms and cyclic voltammetric (CV). The results showed that MWCNTs, MWCNT-COOH and MWCNT-NH₂ exhibited good biocompatibility on exoelectrogenic bacteria. The performance of MFCs were improved through the introduction of MWCNT-modified anodes, especially in the presence of COOH/NH₂ groups. The MFCs with the MWCNTCOOHmodified anode achieved a maximum power density of 560.40 mW/m², which was 49% higher than that obtained with pure carbon cloth. In conclusion, the positive effects of MWCNTs and their functionality were evaluated for promoting biofilm formation, biodegradation and electron transfer on anodes. Specifically, the MWCNTCOOHmodified anode demonstrated the largest application potential for the development of MFCs.     

Platinum-decorated palladium-nanoflowers as high efficient low platinum catalyst towards oxygen reduction

A three-dimensional, low platinum (Pt) catalyst was prepared by decorating platinum on the palladium nanoflowers (PdNF) by an underpotential deposition (UPD) method. The PdNF was synthesized by a solvothermal approach, using oleic acid as the template and benzyl alcohol as the solvent-reducing agent. The obtained Pd with a morphology of uniform nanoflowers is composed of plentiful nanosheets. After decorating with platinum, the catalyst PdNF@Pt exhibits much higher activity for the oxygen reduction reaction (ORR) compared to commercial Pt/C (Pt 20 wt%). The interaction between deposited Pt and PdNF was revealed by XPS analysis, and the high performance of the PdNF@Pt catalyst was attributed to following two aspects: the increased of dispersion of platinum based on PdNF substrate, and the increased intrinsic activity of the active sites caused by the interaction of Pt and Pd NF.     

Ruthenium catalyst supported on Ba modified ZrO2 for ammonia decomposition to COx-free hydrogen

The Ba modified ZrO₂ materials were prepared and loaded Ru nanoparticles for ammonia decomposition to CO_x-free hydrogen reaction. The catalytic activity of Ru supported on BaZrO₂ derived from sol-gel process (Ru/BaZrO₂) is found to be several times of those for Ru/ZrO₂ without any promoter and RuBa/ZrO₂ catalysts prepared by conventional immersion method at the identical conditions. It is found that the formation of BaZrO₃ phase in BaZrO₂ can enhance the electron-donating ability of the support and Ru nanoparticles dispersion. Therefore, mobile electrons would be transferred from BaZrO₃ to the surface Ru particles, facilitating the recombinative desorption of N over Ru particles, leading to the increase of activity for ammonia decomposition sufficiently. Additionally, the suitable size of spherical Ru particles with average size of 2.4 nm for the formation of active sites are also responsible factors for the higher activity of this catalyst. The catalytic performance of Ru/BaZrO₂ catalyst can also be further improved by introducing of K and Cs promoters, and the apparent activation energies over Ru/BaZrO₂ of 94.1 kJ/mol decrease to 70.7 kJ/mol and 64.2 kJ/mol for K and Cs promoted Ru/BaZrO₂, respectively.     

Exploration of Ti substitution in AB2-type YZrFe based hydrogen storage alloys

To improve the hydrogen storage properties of YZrFe alloys, the alloying with Ti was carried out to obtain Y_0.7Zr_(0.3-x)Ti_xFe₂ (x = 0.03, 0.09, 0.1, 0.2) alloys by different processes. It was expected that Ti would substitute Zr and decrease the lattice constant of YFe₂-based C15 Laves phase. All YZrTiFe quaternary alloys consist of the main Y(Zr)Fe₂ phase and the minor YFe₃ phase. Despite the large solubility of Ti in Zr or Zr in Y, the Ti incorporation into YZrFe alloys results in the inhomogeneity of Y and the segregation of Ti, and thus decreases the hydrogen storage capacity. Only the alloy Y_0.7Zr_0.27Ti_0.03Fe₂ containing very few Ti shows the substitution of Ti to Zr and the resultant improvement in the dehydriding equilibrium pressure.