Kinetic study on nonisothermal dehydrogenation of TiH2 powders

The nonisothermal dehydrogenation of TiH₂ powders was studied using thermogravimetry and differential scanning calorimetry. The reaction model was established by estimating the activation energy. The results show the nonisothermal dehydrogenation occurred in a four-step process. The hydrogen released from the TiH_1.5∼2$\text{Ti}{\mathrm{H}}_{1.5\sim 2}$ phase in the first step, which led to the decrease of activation energy. The second step was derived from the formation of βH${\beta }_H$ in δ$\delta$ phase and the reaction model was Phase boundary reaction. In the third step, the hydrogen started to release from the βH${\beta }_H$ phase, and then the βH→αH${\beta }_{\mathrm{H}}\to {\alpha }_{\mathrm{H}}$ phase transformation happened. So the activation energy Eα$E_{\alpha }$ underwent a decrease followed by a quick increase. The fourth step corresponded to the formation of αH${\alpha }_H$ in βH${\beta }_H$ phase, and the slight oxidation resulted in the small fluctuation of activation energy.     

H2 production with ultra-low CO selectivity via photocatalytic reforming of methanol on Au/TiO2 catalyst

_H2${\mathrm{H}}_2$ with ultra-low CO concentration was produced via photocatalytic reforming of methanol on Au/_TiO2$\mathrm{Au}/{\mathrm{TiO}}_2$ catalyst. The rate of _H2${\mathrm{H}}_2$ production is greatly increased when the gold particle size is reduced from 10 to smaller than 3 nm. The concentration of CO in _H2${\mathrm{H}}_2$ decreases with reducing the gold particle size of the catalyst. It is suggested that the by-product CO is mostly produced via decomposition of the intermediate formic acid species derived from methanol. The smaller gold particles possibly switch the HCOOH decomposition reaction mainly to _H2${\mathrm{H}}_2$ and _CO2${\mathrm{CO}}_2$ products while suppress the CO and _H2${\mathrm{H}}_2$O products. In addition, some CO may be oxidized to _CO2${\mathrm{CO}}_2$ by photogenerated oxidizing species at the perimeter interface between the small gold particles and _TiO2${\mathrm{TiO}}_2$ under photocatalytic condition.     

Investigation on the structure and electrochemical properties of the laser sintered La0.7Mg0.3Ni3.5 hydrogen storage alloys

The structure and electrochemical properties of the _{La0.7Mg0.3Ni3.5}${\mathrm{La}}_{0.7}{\mathrm{Mg}}_{0.3}{\mathrm{Ni}}_{3.5}$ alloys laser sintered at different powers were investigated. It is found that all alloys contain three phases _La3MgNi14${\mathrm{La}}_3{\mathrm{MgNi}}_{14}$ with the _Ce2Ni7${\mathrm{Ce}}_2{\mathrm{Ni}}_7$ structure, _LaNi5${\mathrm{LaNi}}_5$ and _LaMgNi4${\mathrm{LaMgNi}}_4$. The abundance of the main phase _La3MgNi14${\mathrm{La}}_3{\mathrm{MgNi}}_{14}$ is 43, 68 and 63 wt%, respectively, when sintering power varies from 1000 to 1200 and 1400 W. The laser sintered _{La0.7Mg0.3Ni3.5}${\mathrm{La}}_{0.7}{\mathrm{Mg}}_{0.3}{\mathrm{Ni}}_{3.5}$ alloys can be activated to their maximum discharge capacity within three cycles. The discharge capacities of those alloys prepared by laser sintering at 1000, 1200 and 1400 W are 324.6, 352.8 and 340.5 mAh/g, respectively. The _{La0.7Mg0.3Ni3.5}${\mathrm{La}}_{0.7}{\mathrm{Mg}}_{0.3}{\mathrm{Ni}}_{3.5}$ alloy laser sintered at 1200 W has a best cyclic stability (_S100=58.4%)$(S_{100}=58.4\%)$ and high-rate dischargeability (_HRD800=79.4%)$({\mathrm{HRD}}_{800}=79.4\%)$ due to the high amount of the main phase _La3MgNi14${\mathrm{La}}_3{\mathrm{MgNi}}_{14}$.     

CO2 reforming of CH4 by combination of thermal plasma and catalyst

Experiments on synthesis gas preparation from dry reforming of methane by carbon dioxide with thermal plasma only and cooperation of thermal plasma with commercial catalysts have been performed. In all experiments, nitrogen gas was used as the plasma gas to form a high-temperature jet injected into a tube reactor. A mixture of _CH4${\mathrm{CH}}_4$ and _CO2${\mathrm{CO}}_2$ was fed vertically into the jet. Both kinds of experiments were conducted in the same conditions, such as total flux of feed gases, the molar ratio of _CH4/_CO2${\mathrm{CH}}_4/{\mathrm{CO}}_2$, and the plasma power except with or without catalysts in the tube reactor. Higher conversion of _CH4${\mathrm{CH}}_4$ and _CO2${\mathrm{CO}}_2$, higher selectivity of _H2${\mathrm{H}}_2$ and CO, and higher specific energy of the process were achieved by thermal plasma with catalysts. For example, the conversions of _CH4${\mathrm{CH}}_4$ and _CO2${\mathrm{CO}}_2$ were high to 96.33% and 84.63%, and the selectivies of CO and _H2${\mathrm{H}}_2$ were also high to 91.99% and 74.23%, respectively. Both were 10–20%$10–20\%$ higher than those by thermal plasma only.     

Comparisons between MgH2- and LiH-containing systems for hydrogen storage applications

The present study compares the dehydrogenation kinetics of (2_LiNH2+_MgH2)$(2{\mathrm{LiNH}}_2+{\mathrm{MgH}}_2)$ and (_LiNH2+LiH)$({\mathrm{LiNH}}_2+\mathrm{LiH})$ systems and their vulnerabilities to the NH₃ emission problem. The (2_LiNH2+_MgH2)$(2{\mathrm{LiNH}}_2+{\mathrm{MgH}}_2)$ and (_LiNH2+LiH)$({\mathrm{LiNH}}_2+\mathrm{LiH})$ mixtures with different degrees of mechanical activation are investigated in order to evaluate the effect of mechanical activation on the dehydrogenation kinetics and NH₃ emission rate. The activation energy for dehydrogenation, the phase changes at different stages of dehydrogenation, and the level of NH₃ emission during the dehydrogenation process are studied. It is found that the (2_LiNH2+_MgH2)$(2{\mathrm{LiNH}}_2+{\mathrm{MgH}}_2)$ mixture has a higher rate for hydrogen release, slower rate for approaching a certain percentage of its equilibrium pressure, higher activation energy, and more NH₃ emission than the (_LiNH2+LiH)$({\mathrm{LiNH}}_2+\mathrm{LiH})$ mixture. On the basis of the phenomena observed, the reaction mechanism for the dehydrogenation of the (2_LiNH2+_MgH2)$(2{\mathrm{LiNH}}_2+{\mathrm{MgH}}_2)$ system has been proposed for the first time. Approaches for further improving the hydrogen storage behavior of the (2_LiNH2+_MgH2)$(2{\mathrm{LiNH}}_2+{\mathrm{MgH}}_2)$ system are discussed in light of the newly proposed reaction mechanism.     

A comparison of hydrogen storage technologies for solar-powered stand-alone power supplies: A photovoltaic system sizing approach

This paper compares the performance of three different solar based technologies for a stand-alone power supply (SAPS) using different methods to address the seasonal variability of solar insolation—(i) photovoltaic (PV) panels with battery storage; (ii) PV panels with electrolyser and hydrogen (_H2)$({\mathrm{H}}_2)$ storage; and (iii) photoelectrolytic (PE) dissociation of water for _H2${\mathrm{H}}_2$ generation and storage. The system size is determined at three different Australian locations with greatly varying latitudes—Darwin (12^°S${12}^{°}\mathrm{S}$), Melbourne (38^°S${38}^{°}\mathrm{S}$) and Macquarie Island (55^°S${55}^{°}\mathrm{S}$). While the PV/electrolyser system requires fewer PV panels compared to the PV/battery scenario due to the seasonal storage ability of _H2${\mathrm{H}}_2$, the final number of PV modules is only marginally less at the highest latitude due to the lower energy recovery efficiency of _H2${\mathrm{H}}_2$ compared to batteries. For the PE technology, an upper limit on the cost of such a system is obtained if it is to be competitive with the existing PV/battery technology.     

Kinetic characteristics of sodium borohydride formation when sodium meta-borate reacts with magnesium and hydrogen

Sodium borohydride is attracting considerable interests as a hydrogen storage medium. In this paper, we investigated the effects of hydrogen pressure, reaction temperature and transition metal addition on sodium borohydride synthesis by the reaction of sodium meta-borate with Mg and _H2${\mathrm{H}}_2$. It was found that higher _H2${\mathrm{H}}_2$ pressure was beneficial to _NaBH4${\mathrm{NaBH}}_4$ formation. The increase in reaction temperature first improved _NaBH4${\mathrm{NaBH}}_4$ formation kinetics but then impeded it when the temperature was raised to near the melting point of Mg. It was also found that some additions of transition metals such as Ni, Fe and Co in the _NaBO2+Mg+_H2${\mathrm{NaBO}}_2+\mathrm{Mg}+{\mathrm{H}}_2$ system promoted the _NaBH4${\mathrm{NaBH}}_4$ formation, but Cu addition showed little effect. The activation energy of the _NaBH4${\mathrm{NaBH}}_4$ formation from Mg, _NaBO2${\mathrm{NaBO}}_2$ and _H2${\mathrm{H}}_2$ was estimated to be 156.3 kJ/mol _NaBH4${\mathrm{NaBH}}_4$ according to Ozawa analysis method.     

The ignition,combustion and flame structure of carbon monoxide/hydrogen mixtures. Note 1: Detailed kinetic modeling of syngas combustion also in presence of nitrogen compounds

The kinetic characterization of the _H2/CO${\mathrm{H}}_2/\mathrm{CO}$ system is of interest right now due mainly to its role in sustainable combustion processes. The aim of this paper is to revise and validate a detailed kinetic model of hydrogen and carbon monoxide mixture combustion with particular focus not only on _NOx${\mathrm{NO}}_x$ formation but also on interactions with nitrogen species. Model predictions and experimental measurements are discussed and compared across a wide range of operating conditions. This study moves from the detailed analysis of species profiles in syngas oxidation in flow reactor and laminar premixed flames to global combustion properties (ignition delay times and laminar flame speeds) by referring to a large set of literature data. According to recent literature, the validation of the kinetic scheme confirmed there was a need to slightly modify the kinetic parameters of two relevant _CO2${\mathrm{CO}}_2$ formation reactions (CO+OH=_CO2+H$\mathrm{CO}+\mathrm{OH}={\mathrm{CO}}_2+\mathrm{H}$ and CO+O+M=_CO2+M$\mathrm{CO}+\mathrm{O}+\mathrm{M}={\mathrm{CO}}_2+\mathrm{M}$) and of reaction HONO+OH=_NO2+_H2O$\mathrm{HONO}+\mathrm{OH}={\mathrm{NO}}_2+{\mathrm{H}}_2\mathrm{O}$.     

Hydrogen production by autothermal reforming of LPG for PEM fuel cell applications

Indirect partial oxidation, or oxidative steam reforming, tests of a bimetallic Pt–Ni catalyst supported on δ$\delta$-alumina were conducted in propane–n  -butane mixtures (LPG) used as feed. _H2${\mathrm{H}}_2$ production activity and _H2/CO${\mathrm{H}}_2/\mathrm{CO}$ selectivity were investigated in response to different S/C, C/_O2$\mathrm{C}/{\mathrm{O}}_2$ and W/F ratios. It was confirmed that higher steam content in the reactant stream increases both the activity and the _H2/CO${\mathrm{H}}_2/\mathrm{CO}$ selectivity of the process. Low residence times created a positive impact on catalyst activity not only for hydrogen but also for carbon monoxide production due to the increased amount of fresh hydrocarbon in the feed stream. Hence, the highest selectivity level was obtained at intermediate residence times. The response of the system to C/_O2$\mathrm{C}/{\mathrm{O}}_2$ ratio was found to depend on the available steam content due to the complex nature of IPOX. The Pt–Ni catalyst was very prone to catalyst deactivation at low S/C ratios accompanied by high C/_O2$\mathrm{C}/{\mathrm{O}}_2$ ratios, but this problem was not encountered at high S/C ratios. A comparison of catalyst performance for different propane-to-n-butane ratios in the LPG feed indicated that the Pt–Ni catalyst has slightly better activity and selectivity at higher n-butane contents at the expense of becoming more sensitive to coke deposition.     

Catalytic hydrogen storage in cerium nickel and zirconium (or aluminium) mixed oxides

Interaction of hydrogen with a series of cerium nickel and zirconium (or aluminium) mixed oxides _CeM0.5NixOy${\mathrm{CeM}}_{0.5}{\mathrm{Ni}}_x{\mathrm{O}}_y$ (M=Zr$\mathrm{M}=\mathrm{Zr}$ or Al, 0?x?3$0?x?3$) has been studied in the 50–800 °C temperature range. Hydrogenation of 2-methyl-1,3-diene (isoprene) under helium flow in the absence of gaseous hydrogen is used to reveal and titrate reactive hydrogen species present in the solid previously treated under _H2${\mathrm{H}}_2$ at various temperatures. The _CeM0.5NixOy${\mathrm{CeM}}_{0.5}{\mathrm{Ni}}_x{\mathrm{O}}_y$ mixed oxides are large catalytic hydrogen reservoirs and among the solids studied, the highest amount of hydrogen (about 10 wt%, 540 g/L) is stored in _CeZr0.5Ni1Oy${\mathrm{CeZr}}_{0.5}{\mathrm{Ni}}_1{\mathrm{O}}_y$ pretreated in _H2${\mathrm{H}}_2$ at about 200 °C. Compared to the binary mixed oxides _CeNixOy${\mathrm{CeNi}}_x{\mathrm{O}}_y$, the presence of M allows to increase the hydrogen storage and give a better stability to the system, in particular, with temperature. Different physico-chemical techniques (TPR, TGA …) have been used to characterize the solids studied.