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.     

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.     

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.     

Demonstration of sustained hydrogen photoproduction by immobilized,sulfur-deprived Chlamydomonas reinhardtii cells

It was demonstrated that immobilized, sulfur-deprived algal cultures can photoproduce H₂${}_2$. After identifying the optimal material and procedures for immobilization of Chlamyodomonas reinhardtii   at high cell density, we examined the effect of liquid mixing, sulfate content, acetate levels and light intensity on the H₂${}_2$-production activity of the culture. Our results indicate that (a) liquid mixing is important to provide homogeneous conditions for the immobilized culture; (b) sulfur deprivation is necessary for hydrogen production by immobilized cultures; and (c) high light intensity decreases H₂${}_2$ production. The maximum total volume of H₂${}_2$ produced by the system (160 ml of reactor volume) was 380 ml over 23 days, and the highest rate of H₂${}_2$ production observed was 45 ml day^-1${}^{-1}$. Cell immobilization significantly increased the duration of the H₂${}_2$-photoproduction phase (up to 4 weeks), maintained specific rates of H₂${}_2$ photoproduction similar to those of suspension cultures and showed potential for large increases in H₂${}_2$ production.     

Analysis of H2 to CO2 yield and physiological key parameters of Enterobacter aerogenes and Caldicellulosiruptor saccharolyticus

In our study two strains, Enterobacter aerogenes and Caldicellulosiruptor saccharolyticus, were chosen as model microorganisms for investigation of biohydrogen production. By using E. aerogenes, operated in repetitive batch mode, the highest cumulative volumetric hydrogen evolution rate was obtained at an initial glucose concentration of 13.7 g/L. Growing C. saccharolyticus in repetitive batch mode on xylose revealed that complex media resulted in higher volumetric hydrogen productivities but lower hydrogen yields than defined media. Chemostat culture investigations of E. aerogenes and C. saccharolyticus on glucose revealed that higher dilution rates resulted in higher biohydrogen productivities, but also in lower product yields. The highest hydrogen volumetric productivities were obtained with E. aerogenes  , while the highest product to substrate yield (Y₍H₂/s₎)$\left({\text{Y}}_{\left({\text{H}}_2\text{/s}\right)}\right)$ and hydrogen to carbon dioxide yield (Y₍H₂/CO₂₎)$\left({\text{Y}}_{\left({\text{H}}_2{\text{/CO}}_2\right)}\right)$ were obtained with C. saccharolyticus  . Y₍H₂/CO₂₎${\text{Y}}_{\left({\text{H}}_2{\text{/CO}}_2\right)}$ is an important physiological parameter, regarding a future integration of biohydrogen production into the 5th generation of biofuels.     

Evaluation of conversion efficiency of light to hydrogen energy by Anabaena variabilis

Cyanobacteria provide an efficient system for producing _H2${\mathrm{H}}_2$ from water using solar energy. The energy conversion efficiency can be defined by the ratio of _H2${\mathrm{H}}_2$ produced to the light energy absorbed. An IR and opalescent plate method was used to measure the light energy absorbed. Since cyanobacteria absorb light in the visible range but not in the infrared range, the net amount of light energy absorbed by the cells can be estimated by measuring the IR and visible light intensities transmitted through the biochamber. A rectangular biochamber was used for measuring the conversion efficiency from light energy to _H2${\mathrm{H}}_2$ energy. A quantum meter and radiometer were used to measure the light intensity transmitted through the chamber. Anabaena variabilis was cultured in a BG11 medium with 3.6 mM NaNO₃${}_3$ and the light intensity was 40–50 μmol/m²/s$\mathrm{\mu }\mathrm{mol}/{\mathrm{m}}^2/\mathrm{s}$ in the growth phase and 120–140 μmol/m²/s$\mathrm{\mu }\mathrm{mol}/{\mathrm{m}}^2/\mathrm{s}$ in the _H2${\mathrm{H}}_2$ production phase. The maximum _H2${\mathrm{H}}_2$ production was 50 ml for 40 h and cell density was 1.2 g/l. The _H2${\mathrm{H}}_2$ production rate was 4.1 ml _H2/g${\mathrm{H}}_2/\mathrm{g}$ dry cell weight/h. Based on the light absorbed in the _H2${\mathrm{H}}_2$ production phase, the energy conversion efficiency from light to _H2${\mathrm{H}}_2$ was 1.5% on average and 3.9% at the maximum. Based on the light energy absorbed in the cell growth and _H2${\mathrm{H}}_2$ production phases, the energy conversion efficiency was 1.1% on average.     

Measurements and kinetic study on ignition delay times of propane/hydrogen in argon diluted oxygen

Measurements on ignition delay times of propane/hydrogen mixtures in argon diluted oxygen were conducted for hydrogen fractions in the fuel mixtures (XH₂)$\left(X_{{\text{H}}_2}\right)$ from 0 to 100%, pressures of 1.2, 4.0 and 10 atm, and temperatures from 1000 to 1600 K using the shock-tube. Results show that for XH₂$X_{{\text{H}}_2}$ less than 70%, ignition delay time shows a strong Arrhenius temperature dependence and it decreases with the increase of pressure, while for XH₂$X_{{\text{H}}_2}$ larger than 90%, there is a crossover pressure dependence of the ignition delay time with increasing temperature. Numerical studies were made using the selected kinetic mechanisms and results show that the predicted ignition delay time gives a reasonable agreement with the measurements. Both measurements and predictions show that for XH₂$X_{{\text{H}}_2}$ less than 70%, the ignition delay time is only moderately decreased with the increase of XH₂$X_{{\text{H}}_2}$, indicating that hydrogen addition has weak effect on ignition enhancement. Sensitivity analysis reveals the key reactions that control the simulation of ignition delay time. Kinetic study is made to interpret the ignition delay time dependence on pressure and XH₂$X_{{\text{H}}_2}$.     

Development of TiO2-supported nano-RuO2-incorporated catalytic nickel coating for hydrogen evolution reaction

Composite nickel coated steel cathodes were fabricated for hydrogen evolution reaction. _TiO2${\mathrm{TiO}}_2$-supported _RuO2${\mathrm{RuO}}_2$ particles of varying size were incorporated in the electroless coating. The electrodes exhibited high catalytic activity which was dependent on the size of _RuO2${\mathrm{RuO}}_2$ particles incorporated. The smaller the size at nano-level, the higher the catalytic activity. There was enhanced hydrogen adsorption due to high surface roughness and abundant active sites.     

Changes of hydrogen storage properties of MgH2 induced by heavy ion irradiation

In order to understand the influence of defect zones on desorption behavior of _MgH2${\mathrm{MgH}}_2$, Xe 120 keV ion irradiation of this material has been performed. DSC, SEM measurements, and SRIM calculations have been used to characterize induced modifications and its influence on the hydrogen desorption behavior of _MgH2${\mathrm{MgH}}_2$. We have demonstrated that the near-surface area of _MgH2${\mathrm{MgH}}_2$ plays the crucial role in hydrogen desorption kinetics. DSC analysis provides clear picture of vacancies influence on H diffusion and desorption in _MgH2${\mathrm{MgH}}_2$, and points out that there is possibility to control the thermodynamic parameters by controlled ion bombardment.     

Study on laminar flame speed and flame structure of syngas with varied compositions using OH-PLIF and spectrograph

Various Bunsen flame information of premixed syngas/air mixtures was systematically collected. A CCD camera was used to capture the flame images. The OH-PLIF technique was applied to obtain the flame OH distribution and overall flame radiation spectra were measured with a spectrograph. Experiments were conducted on a temperature un-controlled burner and syngas over a wide range of H₂/CO ratios (from 0.25 to 4) and equivalence ratios (from 0.5 to 1.2). Results show that increasing hydrogen fraction (XH₂$X_{{\text{H}}_2}$) extends the blow-off limit significantly. The measured laminar flame speed using cone-angle method based on CCD flame imaging and OH-PLIF images increases remarkably with the increase of XH₂$X_{{\text{H}}_2}$, and these measurements agrees well with kinetic modeling predictions through Li's mechanism when the temperature for computation is corrected. Kinetic study shows that as XH₂$X_{{\text{H}}_2}$ increases, the production of H and OH radicals is accelerated. Additionally, the main H radical production reaction (or OH radical consumption reactions) changes from R29 (CO + OH = CO₂ + H) to R3 (H₂ + OH = H₂O + H) as XH₂$X_{{\text{H}}_2}$ increases. Sensitivity analysis was conducted to access the dominant reactions when XH₂$X_{{\text{H}}_2}$ increases. The difference on flame color for different XH₂$X_{{\text{H}}_2}$ mixtures is due to their difference in radiation spectrum of the intermediate radicals produced in combustion.     

Fuel-rich methane oxidation in a high-pressure flow reactor studied by optical-fiber laser-induced fluorescence,multi-species sampling profile measurements and detailed kinetic simulations

A versatile flow-reactor design is presented that permits multi-species profile measurements under industrially relevant temperatures and pressures. The reactor combines a capillary sampling technique with a novel fiber-optic Laser-Induced Fluorescence (LIF) method. The gas sampling provides quantitative analysis of stable species by means of gas chromatography (i.e. _CH4${\mathrm{CH}}_4$, _O2,CO,_CO2${\mathrm{O}}_2\text{,}\mathrm{CO}\text{,}{\mathrm{CO}}_2$, _H2O,_H2${\mathrm{H}}_2\mathrm{O}\text{,}{\mathrm{H}}_2$, _C2${\mathrm{C}}_2$_H6${\mathrm{H}}_6$, _C2${\mathrm{C}}_2$_H4${\mathrm{H}}_4$), and the fiber-optic probe enables in situ detection of transient LIF-active species, demonstrated here for C_H2${\mathrm{H}}_2$O. A thorough analysis of the LIF correction terms for the temperature-dependent Boltzmann fraction and collisional quenching are presented. The laminar flow reactor is modeled by solving the two-dimensional Navier–Stokes equations in conjunction with a detailed kinetic mechanism. Experimental and simulated profiles are compared. The experimental profiles provide much needed data for the continued validation of the kinetic mechanism with respect to _C1${\mathrm{C}}_1$ and _C2${\mathrm{C}}_2$ chemistry; additionally, the results provide mechanistic insight into the reaction network of fuel-rich gas-phase methane oxidation, thus allowing optimization of the industrial process.     

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${\mathrm{La}}_3{\mathrm{MgNi}}_{14}$.     

Effects of metal oxides addition on the performance of La1.3CaMg0.7Ni9 hydrogen storage alloy

The _{La1.3CaMg0.7Ni9}${\mathrm{La}}_{1.3}{\mathrm{CaMg}}_{0.7}{\mathrm{Ni}}_9$ alloy was modified with various metal oxides (_Fe2O3${\mathrm{Fe}}_2{\mathrm{O}}_3$, _TiO2${\mathrm{TiO}}_2$, _Cr2O3${\mathrm{Cr}}_2{\mathrm{O}}_3$, ZnO), and the effects of metal oxides addition on the electrochemical properties of the _{La1.3CaMg0.7Ni9}${\mathrm{La}}_{1.3}{\mathrm{CaMg}}_{0.7}{\mathrm{Ni}}_9$ hydrogen storage alloy were investigated. The catalytic effects of metal oxides are found. Not only the discharge capacity but also the high-rate dischargeability (HRD) is improved by addition of 5 wt% _TiO2${\mathrm{TiO}}_2$, _Cr2O3${\mathrm{Cr}}_2{\mathrm{O}}_3$, and ZnO, while the cyclic stability does not change except for addition of _Fe2O3${\mathrm{Fe}}_2{\mathrm{O}}_3$. The low-temperature property is enhanced more obviously by addition of _TiO2${\mathrm{TiO}}_2$, _Cr2O3${\mathrm{Cr}}_2{\mathrm{O}}_3$, and ZnO. The electrochemical kinetics is also measured by the linear polarization and electrochemical impedance spectroscopy (EIS). In addition, the hydrogen absorption kinetic behavior is measured by gas–solid reaction.     

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$\mathrm{HONO}+\mathrm{OH}={\mathrm{NO}}_2+{\mathrm{H}}_2\mathrm{O}$.