Enhanced Hydrogen Ab/De-sorption of Mg(Zn) solid solution alloy catalyzed by YH2/Y2O3 nanocomposite

YH₂/Y₂O₃ nanocomposite was prepared and introduced to Mg_0.97Zn_0.03 solid solution alloy forming a nanocomposite of Mg_0.97Zn_0.03-10 wt%YH₂/Y₂O₃ by mechanical milling. The phase components and microstructure were systematically investigated by XRD, SEM and STEM. Hydrogenation of Mg_0.97Zn_0.03 solid solution resulted in phase segregation into MgH₂ and intermetallic compound MgZn₂. The in-situ formed ultra-fine MgZn₂ homogeneously dispersed in MgH₂ matrix, and returned to Mg(Zn) solid solution through dehydrogenation. This reversible phase transition of Mg(Zn) solid solution benefited to thermodynamic destabilization of MgH₂. The co-dopant of YH₂ and Y₂O₃ exhibited synergistic catalytic effects on the hydrogen absorption and desorption of Mg_0.97Zn_0.03 solid solution alloy. As a result, Mg_0.97Zn_0.03-10 wt%YH₂/Y₂O₃ nanocomposite showed significantly improved kinetics with obviously lowered hydriding and dehydriding activation energy of 45.8 kJ⋅mol⁻¹⋅H₂ and 74.7 kJ⋅mol⁻¹⋅H₂, respectively, and the enthalpy of hydrogen desorption was reduced to 72.2 kJ⋅mol⁻¹⋅H₂.     

Kinetic studies of dehydration,pyrolysis and combustion of paper sludge

The reaction kinetics of drying, pyrolysis and combustion of paper sludge have been determined in a thermogravimetric analyzer (TGA). The effects of heating rate (5–30 K min⁻¹) and sample weight (10–50 mg) on drying and pyrolysis of paper sludge have been determined. The kinetic parameters of char combustion are determined at the isothermal conditions (723–1173 K). For dehydration, pyrolysis and combustion of paper sludge, temperature can be divided into drying (−470 K), pyrolysis [low (470–660 K), medium (660–855 K)] and combustion (>855 K) ranges. From the kinetic parameters (frequency factor and activation energy) of water decomposition, two major degradable compounds are found and the experimental thermogravimetric curves predicted by those parameters. For char combustion, the reaction order is found to be unity. The char combustion is well expressed by the shrinking core model with chemical reaction controlling and the activation energy is changed from 24.3 to 10.14 kJ mol⁻¹ K⁻¹ at 873 K.     

New mechanism and improved kinetics of hydrogen absorption and desorption of Mg(In) solid solution alloy milling with CeF3

This paper presents improving the hydrogen absorption and desorption of Mg(In) solid solution alloy through doped with CeF₃. A nanocomposite of Mg_0.95In_0.05-5 wt% CeF₃ was prepared by mechanical ball milling. The microstructures were systematically investigated by X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy. And the hydrogen storage properties were evaluated by isothermal hydrogen absorption and desorption, and pressure-composition-isothermal measurements in a temperature range of 230 °C–320 °C. The mechanism of hydrogen absorption and desorption of Mg_0.95In_0.05 solid solution is changed by the addition of CeF₃. Mg_0.95In_0.05-5 wt% CeF₃ nanocomposite transforms to MgH₂, MgF₂ and intermetallic compounds of MgIn and CeIn₃ by hydrogenation. Upon dehydrogenation, MgH₂ reacts with the intermetallic compounds of MgIn and CeIn₃ forming a pseudo-ternary Mg(In, Ce) solid solution, which is a fully reversible reaction with a reversible hydrogen capacity～4.0 wt%. The symbiotic nanostructured CeIn₃ impedes the agglomeration of MgIn compound, thus improving the dispersibility of element In, and finally improving the reversibility of hydrogen absorption and desorption of Mg(In) solution alloy. For Mg_0.95In_0.05-5 wt% CeF₃ nanocomposite, the dehydriding enthalpy is reduced to about 66.1 ± 3.2 kJ⋅mol⁻¹⋅H₂, and the apparent activation energy of dehydrogenation is significantly lowered to 71.9 ± 10.0 kJ⋅mol⁻¹⋅H₂, a reduction of ～73 kJ⋅mol⁻¹⋅H₂ relative to that for Mg_0.95In_0.05 solid solution. As a result, Mg_0.95In_0.05-5 wt% CeF₃ nanocomposite can release ～57% H₂ in 10 min at 260 °C. The improvements of hydrogen absorption and desorption properties are mainly attributed to the reversible phase transition of Mg(In, Ce) solid solution combing with the multiphase nanostructure.     

CuO–NiO/Co3O4 hybrid nanoplates as highly active catalyst for ammonia borane hydrolysis

Dehydrogenation of hydrogen-rich chemicals, such as ammonia borane (AB), is a promising way to produce hydrogen for mobile fuel cell power systems. However, the practical application has been impeded due to the high cost and scarcity of the catalysts. Herein, a low-cost and high-performing core-shell structured CuO–NiO/Co₃O₄ hybrid nanoplate catalytic material has been developed for the hydrolysis of AB. The obtained hybrid catalyst exhibits a high catalytic activity towards the hydrolysis of AB with a turnover frequency (TOF) of 79.1 mol_H2 mol cat⁻¹ min⁻¹. The apparent activation energy of AB hydrolysis on CuO–NiO/Co₃O₄ is calculated to be 23.7 kJ.mol⁻¹. The synergistic effect between CuO–NiO and Co₃O₄ plays an important role in the improvement of the catalytic performance. The development of this high-performing and low-cost CuO–NiO/Co₃O₄ hybrid catalytic material can make practical applications of AB hydrolysis at large-scale possible.     

High pressure ammonia dissociation experiments for solar energy transport and storage

Work relating to the application of the ammonia dissociation reaction to the thermochemical transport and storage of solar energy is reported. A two-dimensional pseudo-homogeneous packed-bed catalytic reactor model has been adapted to predict the behaviour of ammonia dissociation and synthesis reactors. A series of steady-state experiments, with a high-pressure ammonia dissociator operated in an ‘open-loop’ experimental configuration, have been used to verify the model. These experiments involved operating pressures up to 16 MPa and temperatures up to 720°C. The results indicated an activation energy of 192 kJ mol⁻¹ and a pre-exponential factor of 3.0 × 10⁷mol s⁻¹ cm⁻³ atm⁻¹ for the nickel-on-alumina dissociation catalyst used. The experiments also indicated that the experimental configuration is suitable for development into a ‘closed-loop’ energy storage experiment operating at a power level of approximately 1kW_chem.     

Physicochemical characterization and pyrolysis kinetics of wood sawdust

In this work, physicochemical characterization of wood sawdust (WSD) has been carried out and kinetics of its pyrolysis has been studied. The physiochemical properties such as proximate and ultimate analysis, lignocellulosic composition, heating value and thermal analysis of WSD have been carried out. The activation energy of the pyrolysis of WSD has been calculated by model-free Kissinger–Akahira–Sunose, Ozawa–Flynn–Wall methods and the average values are found to be 164.24 kJ mol^?1 and 173.41 kJ mol^?1, respectively. Coasts–Reforn method has been used to calculate the pre-exponential factor and reaction order. The predicted degree of conversion of WSD due to heat treatment is found to be in good agreement with experimental conversion data. Physicochemical properties and kinetic parameters support the good potential of WSD as pyrolysis feedstock.     

Thermokinetic modeling of the combustion of carbonaceous particulate matter

The scope of this study was to determine the kinetics (conversion model, preexponential factor and activation energy) of the combustion of two diesel sootlike materials (Printex XE-2B and Flammruss 101) in the presence of an excess of oxygen by dynamic thermogravimetry. A composite kinetic analysis procedure was applied to evaluate the full kinetic triplet from nonisothermal kinetic data. First, the activation energy values were obtained from the Kissinger–Akahira–Sunose isoconversional method. The values were 129 kJ mol⁻¹ (Printex XE-2B) and 144 kJ mol⁻¹ (Flammruss 101). The higher reactivity of Printex XE-2B material was attributed to its markedly greater surface area. The activation energy was found to depend slightly on conversion, suggesting that the combustion was a single-step process for both materials. Second, a comparison of the theoretical masterplots deduced by assuming various conversion models with the experimental masterplots obtained from the kinetic data allowed the selection of the appropriate conversion model of the process. Both materials were found to follow a mechanism based on surface nucleation with subsequent movement of the resulting surface, which was consistent with the penetration of oxygen through the porous structure of the solid samples. Also, the preexponential factors and exact kinetic exponents were evaluated on the basis of predetermined activation energies and conversion models. The adequate consistency of the kinetic triplet was assessed by comparing both experimental and calculated thermoanalytical curves at constant heating rate.     

Determination of kinetic parameters for thermal decomposition of bamboo leaf to extract bio-silica

Bio-silica has many applications due to its high reactivity and pozzolanic properties. The extraction of silica from biomass such as bamboo leaf is usually accomplished by thermal decomposition. Currently, the thermal decomposition requires external heat energy input. In this work, the possibility to reuse the heat released during thermal decomposition to make the process self-sustained is explored. The kinetic parameters of the combustion were determined by fitting thermogravimetric analysis (TGA) data to the Flynn–Wall–Ozawa model, where the corresponding activation energy and frequency factor are 211.7 ± 3.8 kJ mol^?1 and 4.5 × 10¹⁵ s^?1, respectively. The lower heating value of bamboo leaf determined is 8.709 kJ g^?1, which is comparable to common wood fuels. Hence, the heat released in the combustion of bamboo leaf can be reused to make the process self-sustainable.     

Highly selective hydrogen production from propane by Ru–Ni core–shell nanocatalyst deposited on reduced graphene oxide by sequential chemical vapor deposition

A narrow temperature window (160°C-190°C) was identified for the selective deposition of Ru on Ni supported on reduced graphene oxide (rGO) through a sequential chemical vapor deposition (CVD) method. Cyclopentadiene and cyclopentene were identified as decomposition products of nickelocene CVD on rGO, whereas only methane was detected in gaseous products from ruthenocene CVD. Heat treatment converted the selectively deposited Ru on Ni/rGO into Ru–Ni core–shell bimetallic system on the surface of rGO as confirmed by high-resolution transmission electron microscopy. The Ru–Ni/rGO thus prepared produced hydrogen with high selectivity in propane steam reforming performed in the temperature range of 350°C to 850°C. Addition of 3.6% Ru against Ni supported on rGO improved the turnover frequency (TOF) of propane up to 70% to 100% compared to the Ni/rGO catalyst at lower temperatures (350°C-450°C). The presence of Ru lowered the activation energy of propane SR from 65.7 kJ mol⁻¹ for Ni/rGO to 48.7 kJ mol⁻¹ for Ru–Ni/rGO catalyst.     

DESIGN AND PERFORMANCE ANALYSIS OF A METAL HYDRIDE AIR-CONDITIONER

The design and performance aspects of a 3⋅5 kW (1 ton) cooling capacity metal hydride air-conditioner working with a ZrMnFe/MmNi_4⋅5Al_0⋅5 pair are presented. The analysis is based on the heat transfer and reaction kinetics of coupled beds containing ZrMnFe alloy on the hot side and MmNi_4⋅5Al_0⋅5 on the cold side. The effects of important design and operating parameters, viz. cycle and delay times, bed thickness, effective thermal conductivity, air velocity and operating temperatures, on system performance are studied. The performance of the system is characterized by the mass of the alloys required and the COP. The results show that the initial and running costs of the system depend mainly on the internal and external heat transfer characteristics of the hydride heat exchangers. It is shown that a 1 cm ID tube, a cycle time of 3 minutes, an effective thermal conductivity of about 2⋅5 W m⁻¹ K⁻¹ and air velocity of about 3 m s⁻¹ result in optimum performance in terms of alloy inventory and COP. © 1997 by John Wiley & Sons, Ltd.     

Chemical energy storage by the reaction cycle CuO/Cu2O

The cyclic decomposition of cupric oxide followed by the oxidation of cuprous oxide in air was studied, in order to investigate the potential use of this reaction cycle for chemical energy storage. Isothermal and non-isothermal thermogravimetric method was used to study the kinetics of these reactions. The activation energy of the forward reaction (decomposition) is 313.0 kJ mol^?1 in the temperature range 760–910°C, while that for the backward reaction is 76.5 kJ mol^?1 in the temperature range 400–500°C. The reaction reactivity was found to be essentially unchanged for up to 20 cycles. This was explained as due to the swelling of the CuO particles and the development of a highly porous structure on repeated cycling.     

Oxidation of BrCN in shock waves and formation of NO

The oxidation of BrCN has been studied in shock waves over the temperature range 1680–2550K. The kinetics of the oxidation was monitored by following it emission from NO at the wavelength of 5.34 μm. A computer simulation study was performed to determine the important elementary reactions. It was found from this computer study that the NO formation from BrCN oxidation is mainly governed by 9 elementary reactions, and the main reaction in producing NO is NCO+O=NO+CO.The rate constant of this reaction was determined as k₅=10^13.5±0.4 cm³ mol⁻¹ s⁻¹.The rate constants of Br+BrCN=Br₂+CN,were also determined as k₂=10^15.0±0.2 exp[−(157.4±8.7) kj/RT] cm³ mol⁻¹ s⁻¹,k₆=10^13.8±0.4 exp[−(159 kj/RT] cm³ mol⁻¹ s⁻¹.     

The shock tube pyrolysis of pyridine

Fossil fuels such as coal and heavy fuel oils contain up to about 2 per cent by weight of fuel nitrogen, most of this being present in pyridine or pyrolic aromatic structures. Under pyrolytic conditions these ring structures decompose to give HCN and CH₃CN. For present day computer modelling of NO_x formation in flames it is necessary to know the mechanism and rates of reaction. A number of previous studies of pyridine pyrolysis have been undertaken using shock tubes or flow reactors. In this present study a shock tube was used to obtain the kinetics of pyridine decomposition in the range 1590–2335 K and with pressures between 2.2 and 3.4 atm. Two independent sets of data were obtained. One set of results was found to be represented by an Arrhenius rate constant k=10^9.7±0.5 exp (−220.0 kJ mol⁻¹ RT⁻¹)s⁻¹. For the other work k= 10^9.8±0.5 exp (−228.191±18.42 kJ mol⁻¹ RT⁻¹)s⁻¹. In addition, the pyrolysis mixtures of pyridine plus toluene have also been studied to understand the synergistic effects. The results indicated the strong involvement initiated by fission of the pyridine ring system. Copyright © 2000 John Wiley & Sons, Ltd.     

Graphite/rolled graphene oxide/carbon nanotube photoelectrode for water splitting of exhaust car solution

Graphite/rolled graphene oxide/ carbon nanotubes (G/R-GO/CNTs) was prepared and applied as a photoanode for water splitting from exhaust car solution. R-GO was prepared from graphene oxide (GO) using the modified Hummer method after settle down in solution for 2 months to roll out. The R-GO coated the graphite (G) electrode using the dip-coating method to form G/R-GO. Finally, CNTs were prepared on the G/R-GO electrode by using the chemical vapor deposition method to form G/R-GO/CNT electrode. The images of field emission scanning electron microscope show the formation of relatively homogenous and uniform R-GO with an average diameter of about 140 nm. Also, the high density of CNTs was observed with uniform diameters distribution and lengths of CNTs up to several micrometers. The values of the current density of G/R-GO/CNT electrode for water splitting are changed from 0.82 mA cm⁻² in dark to 1.50 mA cm⁻² in light. The value of incident photon-to-current efficiency was 8.4% at 470 nm. The thermodynamic parameters were calculated, in which the activation energy (E_a), enthalpy (ΔH*), and entropy (ΔS*) values were 8.1 kJ mol⁻¹, 29.9 J mol⁻¹, and 56.4 J K⁻¹ mol⁻¹, respectively.     

Study of extraction and pyrolysis of Jordan tar sand

The extraction and pyrolysis of tar sand from Wadi Isal, Jordan have been investigated. Solvent type, mixing time, temperature, particle size and alkali concentration have been identified as important parameters for bitumen recovery. The results show that hot water extraction is ineffective since a small amount of bitumen has been obtained even at 80°C. Kerosene extraction shows a maximum bitumen recovery of about 43% at 80°C and 180–250 μm particle size. The kinetic parameters of pyrolysis have been determined based on first‐order rate expression and their values were in agreement with other published data in the literature. Copyright © 1999 John Wiley & Sons, Ltd.     

Hydrogen generation from alkaline NaBH4 solution using nanostructured Co–Ni–P catalysts

In the present study, nanostructured Co–Ni–P catalysts have been successfully prepared on Cu sheet by electroless plating method. The morphologies of Co–Ni–P catalysts are composed of football-like, granular, mockstrawberry-like and shuttle-like shapes by tuning the depositional pH value. The as-deposited mockstrawberry-like Co–Ni–P catalyst exhibits an enhanced catalytic activity in the hydrolysis of NaBH₄ solution. The hydrogen generation rate and activation energy are 2172.4 mL min⁻¹ g⁻¹ and 53.5 kJ mol⁻¹, respectively. It can be inferred that the activity of catalysts is the result of the synergistic effects of the surface roughness, the particle size and microscopic architectures. Furthermore, the stability of mockstrawberry-like Co–Ni–P catalyst has been discussed, and the hydrogen generation rate remains about 81.4% of the initial value after 5 cycles.     

Room temperature hydrogen generation from hydrolysis of ammonia–borane over an efficient NiAgPd/C catalyst

NiAgPd nanoparticles are successfully synthesized by in-situ reduction of Ni, Ag and Pd salts on the surface of carbon. Their catalytic activity was examined in ammonia borane (NH₃BH₃) hydrolysis to generate hydrogen gas. This nanomaterial exhibits a higher catalytic activity than those of monometallic and bimetallic counterparts and a stoichiometric amount of hydrogen was produced at a high generation rate. Hydrogen production rates were investigated in different concentrations of NH₃BH₃ solutions, including in the borates saturated solution, showing little influence of the concentrations on the reaction rates. The hydrogen production rate can reach 3.6–3.8 mol H₂ mol_cat⁻¹ min⁻¹ at room temperature (21 °C). The activation energy and TOF value are 38.36 kJ/mol and 93.8 mol H₂ mol_cat⁻¹ min⁻¹, respectively, comparable to those of Pt based catalysts. This nanomaterial catalyst also exhibits excellent chemical stability, and no significant morphology change was observed from TEM after the reaction. Using this catalyst for continuously hydrogen generation, the hydrogen production rate can be kept after generating 6.2 L hydrogen with over 10,000 turnovers and a TOF value of 90.3 mol H₂ mol_cat⁻¹ min⁻¹.     

PDMA cryogel beads as a catalyst for hydrogen generation from NaBH4 alcoholysis

Poly[2-(dimethylamino)ethyl methacrylate] cryogel beads were prepared under cryogenic conditions via free radical polymerization and used as a catalyst in the production hydrogen (H₂) from NaBH₄ by alcoholysis. The efficiency of the catalyst was investigated in the range of 0–40 °C by both methanolysis and ethylene glycolysis reactions, and its reuse was tested. Accordingly, it was observed that the methanolysis reaction was faster than the ethylene glycolysis reaction. When the hydrogen generation rate (HGR) values between 0 and 40 °C were compared, it was concluded that the methanolysis reaction rate increased from 1550 to 4800 mL.min⁻¹g⁻¹ and the ethylene glycolysis reaction rate increased from 923 to 3551 mL.min⁻¹g⁻¹. In the alcoholysis reaction catalyzed by PDMA cryogel beads, the activation energy was calculated as 19.34 and 22.77 kJ.mol⁻¹ for the methanolysis and ethylene glycolysis reactions, respectively. After six repetitions, the catalyst activity was calculated over 50% for NaBH₄ methanolysis and ethylene glycolysis.     

Effects of SnO on growth and physical properties of BSCCO whiskers

Abstract

Superconductor whiskers doped with SnO have been fabricated by annealing a melt quenched (Bi₂Sn₁)-223 precursor using suitable heat treatment cycles. Approximately 5 μm thick, 90 μm wide and 5 mm long whiskers were fabricated, and their physical, electrical and magnetic properties were investigated. Crystallisation activation energies of glass phase fabricated were calculated to be 390 kJ mol^–1 using Kissinger method based on the differential thermal analysis data. The T _c value of the whiskers was found to be 94 K from M–T measurement. The magnetisation of whiskers before superconducting transition increased with decreasing temperature, and after superconducting transition, the magnetisation of whiskers decreased, from positive to negative, due to the diamagnetic nature of superconductivity. The change on magnetisation dependence of applied magnetic fields (M–H) showed that whiskers have paramagnetic–diamagnetic multiphase structure.     

Gas evolution and performance assessment of submarine lead/acid batteries

The gas-evolution rates from new and end-of-life lead/acid submarine cells at both open-circuit and under float-charge have been examined, together with the discharge performance of the cells. The evolved gas is found to comprise hydrogen and oxygen only. The open-circuit and float-charge hydrogen-evolution rates vary logarithmically with temperature. The enthalpy of activation for open-circuit hydrogen evolution is ∼ 70 kJ mol⁻¹ for both old and new cells. The open-circuit hydrogen-evolution rate per Ah of rated capacity for new cells is between 0.00636 and 0.105 cm³ h⁻¹ Ah⁻¹ at STP at 20–50 °C, respectively. For old cells, a > three-fold increase is observed; the evolution rate ranges from 0.0237 to 0.361 cm³ h⁻¹ Ah⁻¹ at STP at 20–50 °C, respectively. On float-charge, using an uncompensated float voltage, the hydrogen-evolution rate of new cells is between 0.0166 and 0.241 cm³ h⁻¹ Ah⁻¹ at STP at 20–50 °C, respectively. For old cells, the rates increase to 0.0298–0.903 cm³ h⁻¹ Ah⁻¹ at STP at 20–50 °C, respectively. In contrast, the electrical discharge performance of the cells decreases with age. This suggests that the active area for hydrogen evolution increases with age, but that the active area for electrical discharge decreases. No correlation has been established between hydrogen evolution in individual cells and electrical discharge performance for cells of the same age. The self-discharge rates of the negative plates at 20 °C are 14 and 50% per year for new and old cells, respectively.