Catalytic Combustion Of Hydrogen Research Articles

Heat transfer control of micro-thermoelectric gas sensor for breath gas monitoring

A micro-thermoelectric gas sensor (micro-TGS) uses thermoelectric voltage induced by the catalytic combustion of hydrogen or methane for selective gas detection in breath. This is accomplished under an elevated temperature using a micro-heater built on the same membrane as a hotplate, which enables selective combustion of the target gas. A temperature differential built by the catalyst on the membrane induces the offset voltage (Voff) of the micro-TGS, which limits the amplifier circuit application. In this study, we strived to suppress Voff by an additive integration process of heat dissipation dots prepared using α-Al2O3 paste. In this paper, we discuss the effects of these α-Al2O3 dots on the thermal balance over the micro-TGS membrane by finite element method (FEM) modeling. When the dots were deposited in a symmetrical position to the combustion catalyst, Voff was compensated depending on the size, numbers, and locations of the dots. The micro-TGS heat transfer control by the dots was additionally verified by 3-D FEM modeling. The changes in Voff by the α-Al2O3 dots in FEM modeling were greater than those of the experiments, suggesting the high thermal conductivity of the micro-TGS membrane. The deviation of the membrane thermal conductivity due to the process non-uniformity significantly influenced the Voff; however, it was effectively reduced by the additive integration of dots.

Effect of Catalytic Hydrogen Combustion on Dehydration in a Membrane Reactor. III. Calculation of the Industrial Reactor

Effect of Catalytic Hydrogen Combustion on Dehydration in a Membrane Reactor. III. Calculation of the Industrial Reactor

Role of Hydrogen and Oxygen Activation over Pt and Pd-Doped Composites for Catalytic Hydrogen Combustion.

Removal of excess amount of hydrogen in a catalytic route is a safety measure to be implemented in fuel cell technologies and in nuclear power plants. Hydrogen and oxygen activation are crucial steps for hydrogen combustion that can be achieved by modifying supports with suitable noble metals. In the present study, Pt- and Pd-substituted Co3O4-ZrO2 (CZ) were synthesized using PEG-assisted sonochemical synthesis. Ionic states of Pt and Pd in CZ supports were analyzed by X-ray photoelectron spectroscopy. Pd and Pt improved H2 and O2 activation extensively, which reduced the temperature of 50% conversion (T50%) to 33 °C compared with the support (CZ). The activation energy of PdCZ catalyst was decreased by more than 2 folds (13.4 ± 1.2 kJ mol-1) compared with CZ (34.3 ± 2.3 kJ mol-1). The effect of oxygen vacancies in the reaction mechanism is found to be insignificant with Pt- and Pd-substituted CZ supports. However, oxygen vacancies play an important role when CZ alone was used as catalyst. The importance of hydrogen and oxygen activation as well as the oxygen vacancies in mechanism was studied by H2-TPD, H2-TPR, and in situ FTIR spectroscopy.

The risk of hydrogen explosion in a submarine p.I Catalytic combustion of hydrogen

Abstract The series of articles discuss issues related to conducting high risk projects on the example of modernisation of hydrogen incinerators on a submarine. The article depicts a technical problem situation connected with catalytic hydrogen combustion on a submarine.

Pt-impregnated catalysts on powdery SiC and other commercial supports for the combustion of hydrogen under oxidant conditions

We report the study of the catalytic hydrogen combustion over Pt-impregnated powdery silicon carbide (SiC) using H2PtCl6 as precursor. The reaction was conducted in excess of oxygen. β-SiC was selected for the study because of its thermal conductivity, mechanical properties, chemical inertness and surface area. The obtained Pt particles over SiC were medium size (average particle diameter of 5nm for 0.5wt% Pt). The activity of the Pt-impregnated catalyst over SiC was compared to those obtained in oxidized form over TiO2 and Al2O3 commercial supports (Pt particles very small in size, average particle diameter of 1nm for 0.5wt% Pt in both cases). The case of a SiO2 support was also discussed. Those Pt/SiC particles were the most active because of their higher contribution of surface Pt0, indicating that partially oxidized surfaces have better activity than those totally oxidized in these conditions. SiC was modified with an acid treatment and thus bigger (average particle diameter of 7nm for 0.5wt% Pt) and more active Pt particles were obtained. Durability of the SiC and TiO2 supported catalysts was tested upon 5 cycles and both have shown to be durable and even more active than initially. Exposure to the oxidative reaction mixture activates the catalysts and the effect is more pronounced for the completely oxidized particles. This is due to the surface oxygen chemisorption which activates catalystś surface.

Catalytic combustion of hydrogen for residential heat supply application

Hydrogen can be converted to thermal energy by combustion or to electricity energy by fuel cells. Considering the stringent requirements for safety from fire hazards and elimination of pollutants, the flameless catalytic combustion of hydrogen is favorable over conventional flame combustion for residential heat supply application. This paper reported an industrial-scale heat acquisition system based on hydrogen catalytic combustion. The 1 wt% Pt-loaded glass fiber felts prepared by an impregnation process were used as the combustion catalyst, and a catalytic combustion burner with a capacity of 1 kW was designed. It was found that 100% hydrogen conversion rate could be obtained during the stable combustion stage, and the stable combustion could be achieved by adjusting hydrogen flow rate. The change in H2/air ratio would influence the initial combustion stage but has little impact on the stable combustion stage. A heat efficiency of 80% for hot water supply was obtained based on the present catalytic hydrogen combustion burner. Copyright © 2016 John Wiley & Sons, Ltd.

Development of a novel cooking stove based on catalytic hydrogen combustion

A hydrogen based cooking stove was developed and tested in respect to efficiency, functionality and hydrogen safety. Therefore the developed novel combustion unit technology is based on the catalytic oxidation of hydrogen on a platinum coated highly porous reticulated silicon carbide foam ceramics. Compared to other works [1], premixing of hydrogen and air is avoided, thus providing the basis for safe and reliable operation. With this catalytic combustion technology, no initial hydrogen ignition is required, implying a high application security. Separate air and hydrogen supplies make regulation of temperature and power efficient, simple and save.Catalytic hydrogen oxidation is performed already at room temperature; whereby at high hydrogen load, a small hydrogen slip is detected under cold start conditions, nevertheless in operation this becomes negligible. In order to overcome this issue, a hydrogen flow regulation, based on the hydrogen combustion temperature, was introduced.A heat exchanger is integrated into the exhaust line, in order to recover heat for the incoming air, required for the catalytic combustion. This leads to a stove efficiency of up to 80%, measured according to the DIN EN 30-2-1: 2005–08 test standard and greatly exceeds the postulated standard minimum efficiency of 35%. For comfortable and save use, the combustion unit is mounted under a glass ceramic coverage, as common for conventional electrical stoves.

Monolithic supports based on biomorphic SiC for the catalytic combustion of hydrogen

Application of biomorphic porous SiC monoliths as Pt catalysts supports for the catalytic combustion of hydrogen. Anisotropic thermal behaviour is highlighted.

Kinetic effects of hydrogen addition on the catalytic self-ignition of methane over platinum in micro-channels

The hetero-/homogeneous chemistry coupling of hydrogen and methane over platinum in catalytic micro-channels was investigated numerically for hydrogen–methane–air mixtures with lean methane–air equivalence ratios φ=0.7, 0.8 and 0.9, containing 0–5% hydrogen (on a molar basis). Simulations were carried out with a 2-D computation that included detailed hetero-/homogeneous chemistry and transport, with emphasis on the kinetic effects of hydrogen addition on the catalytic self-ignition of methane. Simulations indicated that hydrogen can successfully cause catalytic self-ignition of methane–air mixtures in micro-channels, eliminating the need for startup devices. While, methane kinetically inhibits catalytic combustion of hydrogen at low hydrogen compositions, and a two-stage catalytic ignition can be observed under certain conditions. A minimum hydrogen composition for catalytic self-ignition of methane–air mixtures is found to be relatively constant, which is at the level of approximately 3.2% molar fraction, irrespective of the methane–air composition. Furthermore, kinetic analysis suggested that this constant is exactly the critical point from thermal effect (preheating region) to kinetic effect (self-ignition region) with the increase of hydrogen composition, resulting in a sharp reduction in ignition temperature, and providing a good startup strategy and an opportunity to self-ignite hydrocarbons. However, once the hydrogen concentration in the feed is sufficiently low, i.e., below the above critical point, external heating is necessary to ignite methane–air mixtures. Finally, surface coverage simulations in catalytic micro-channels revealed that hydrogen promotes methane catalytic combustion because of the increase in free Pt(s) sites, and richer hydrogen composition or lower temperature enhances this kinetic effect.

Investigation of a Pt containing washcoat on SiC foam for hydrogen combustion applications

A commercial Pt based washcoat, used for catalytic methane combustion, was studied supported on a commercial SiC foam as catalytic material (Pt/SiC) for catalytic hydrogen combustion (CHC). Structural and chemical characterization was performed using Electron Microscopy, X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS). The reaction was monitored following water concentration by Fourier Transform Infrared spectra (FTIR). The FTIR method was compared with H2 detection by Gas Cromatography (GC) and has shown to be adequate to study the kinetics of the CHC reaction in steady state under our experimental conditions (very lean 1% (v/v) H2/air mixtures). The catalyst is composed of 5–20nm disperse Pt nanoparticles decorating a mixture of high surface area Al2O3 and small amounts of ceria supported on the SiC foam which also contains alumina as binder. The Pt/SiC catalytic material has demonstrated to be active enough to start up the reaction in a few seconds at room temperature. The material has been able to convert at least 18.5Lhydrogenmin−1gPt−1 at room temperature in conditions of excess of catalyst. The Pt/SiC material was studied after use using XPS and no significant changes on Pt oxidation states were found. The material was characterized from a kinetic point of view. From the conversion-temperature plot a T50 (temperature for 50% conversion) of 34°C was obtained. Activation energy measured in our conditions was 35±1kJmol−1.

Low Pressure Catalytic Combustion of Hydrogen on Palladium

Exhausts of airship fabric bag in the stratosphere such as hydrogen which can be used for fuels by using catalytic combustion method. This can save the extra fuels used in the power system. Pd/γ- Al2O3 catalyst was prepared in this work by impregnation method and the H2 catalytic combustion reaction kinetic was investigated between the pressure of 3.6 kPa and 101.3 kPa. The effects of temperature, pressure and gas composition ratio were studied in the paper. According to the ex- periment results, the increase of temperature increases the H2 conversion. The parameter pres- sure has a positive effect on H2 reaction kinetics and low concentration of H2 in mixtures shows better performance. The dependence of temperature on H2 reaction rate becomes more sensitive in high pressure.

Optimization of a counter-flow microchannel reactor using hydrogen assisted catalytic combustion for steam reforming of methane

The objective of this study is to optimize a microchannel reactor using hydrogen assisted catalytic combustion for steam reforming of methane. Hydrogen assisted catalytic combustion does not require preheating because the catalytic combustion of hydrogen occurs at room temperature. After start-up by hydrogen catalytic combustion, fuels of hydrogen and methane were changed to methane. The geometric configuration of the counter-flow reactor was optimized by the simulation model under steady state condition. The hydrogen flow rate in the counter-flow reactor was also optimized by transient simulations using the response surface methodology. As a result, the counter-flow reactor showed extremely short start-up time because of the optimized configuration and the optimized hydrogen flow rate. Hot spots were avoided because of the hydrogen shut-off after start-up. The operating characteristics of the counter-flow reactor were compared with those of the co-flow reactor.

Effect of catalytic combustion of hydrogen on dehydrogenation in a membrane reactor. II. Dehydrogenation of ethane. Verification of the mathematical model

Thermodynamically coupled dehydrogenation of ethane in a membrane reactor is studied by mathematical modeling. The dehydrogenation of ethane in a membrane reactor with additional combustion of hydrogen is shown to have an advantage over dehydrogenation in a tubular reactor. Verification of the mathematical model of the process is performed.

High pressure kinetics of CH4, CO and H2 combustion over LaMnO3 catalyst

A high pressure kinetic study was carried out in a wide range of operating conditions to study the effects of pressure, temperature, fuel concentration and equivalence ratio on the catalytic combustion of methane, hydrogen and carbon monoxide over a perovskite-based catalyst. A plate type reactor configuration was chosen. This geometry allowed working in a kinetic control avoiding mass transfer limitations if appropriate experimental conditions are chosen. Since especially for GT application it is important to study the ignition phenomenon, which results to be ruled by kinetics, the study of the kinetics of CH4, H2 and CO catalytic combustion was carried out in a range of temperature consistent with the ignition temperatures and global reaction rate equations were derived.

Nanostructured Pd modified Ni/CeO2 catalyst for water gas shift and catalytic hydrogen combustion reaction

Nanostructured Pd-modified Ni/CeO2 catalyst was synthesized in a single step by solution combustion method and characterized by XRD, TEM, XPS, TPR and BET surface analyzer techniques. The catalytic performance of this compound was investigated by performing the water gas shift (WGS) and catalytic hydrogen combustion (CHC) reaction. The present compound is highly active and selective (100%) toward H2 production for the WGS reaction. A lack of CO methanation activity is an important finding of present study and this is attributed to the ionic substitution of Pd and Ni species in CeO2. The creation of oxide vacancies due to ionic substitution of aliovalent ions induces dissociation of H2O that is responsible for the improved catalytic activity for WGS reaction. The combined H2-TPR and XPS results show a synergism exists among Pd, Ni and ceria support. The redox reaction mechanism was used to correlate experimental data for the WGS reaction and a mechanism involving the interaction of adsorbed H2 and O2 through the hydroxyl species was proposed for CHC reaction. The parity plot shows a good correspondence between the experimental and predicted reaction rates.

Three-dimensional direct numerical simulation of turbulent channel flow catalytic combustion of hydrogen over platinum

The turbulent catalytic combustion of a fuel-lean hydrogen/air mixture (equivalence ratio ϕ=0.24) was investigated by means of three-dimensional direct numerical simulation (DNS) in a platinum-coated plane channel with a prescribed wall temperature of 960K and an incoming Reynolds number, based on the channel height, of 5700. Heat transfer from the hot catalytic walls laminarized the flow, as manifested by the progressive suppression of the high vorticity components of the flow aligned parallel to the channel walls at increasing streamwise distances. The impact of turbulence suppression on the mass transfer towards or away from the catalytic wall was subsequently assessed. Far upstream where high turbulence fluctuations persisted, the instantaneous local transverse gradient of the limiting hydrogen reactant (a quantity proportional to the catalytic reaction rate) as well as the instantaneous hydrogen concentration at the wall exhibited strong fluctuations by up to 300%, a result of finite-rate chemistry induced by the high inrush events towards the catalytic walls. Fourier analysis of the reaction rate fluctuations yielded peak frequencies of less than 1kHz, values comparable to the thermal response frequencies of typical materials in commercial catalytic geometries. This has direct implications on the thermal stress of the reactor walls as well as on the decoupling between flow and solid thermal modeling currently used in practical catalytic reactors. Far downstream, the dampening of turbulence resulted in weaker hydrogen concentration fluctuations with nearly symmetric distributions. Finally, computed transverse turbulent species fluxes indicated inherent weaknesses of near-wall turbulence models in describing turbulent transport of species with disparate molecular diffusivities.

Hydrogen catalytic combustion over a Pt/Ce0.6Zr0.4O2/MgAl2O4 mesoporous coating monolithic catalyst

In case of fuel cell vehicle application, hydrogen exhaust is inevitable. The catalytic combustion of hydrogen is considered as one of the most efficient counter-methods. The difficulty is to improve low temperature catalytic behavior of the catalyst and decrease air resistance of the reaction bed. This paper reported a kind of mesoporous ceramic coating monolithic Pt-based catalyst (Pt/Ce0.6Zr0.4O2/MgAl2O4/cordierite) prepared from only inorganic salt and alkali according to the generalized acid–base theory. The coating and catalysts were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), and N2-adsorption. The results showed the coating had typical spinel crystallization structure and high surface area (more than 200 m2 g−1). The Ce–Zr oxide modification increased the surface area and improved the oxygen storage capacity. And the results of hydrogen catalytic combustion indicated that this monolithic catalyst had high activity for hydrogen combustion reaction, which could quickly start up even at 263 K. For low temperature catalytic combustion of hydrogen, the initial reaction temperature, H2 concentration, and space velocity were very important parameters.

Modelling and simulation of a wind-hydrogen CHP system with metal hydride storage

Abstract This paper describes the modelling and simulation of a wind-hydrogen system aimed at supplying electrical and thermal residential loads, where the thermal load is in part supplied by a catalytic hydrogen combustion device with hydrogen stored in a metal hydride system composed of a cluster of five metal hydride tanks equipped with a metal foam heat exchanger. The complete mathematical model has been developed from models available in literature and describing the different sub-systems that constitute the overall wind-hydrogen system. It has been later implemented in a multi-domain software environment to simulate system operations. Results over a year-long simulation show complete stand-alone capabilities, with an electrical efficiency and a combined heat and power efficiency of 8.2% and 12.5% respectively. At the end of the simulation period, a hydrogen annual surplus of 110.5 kg is left over which can, for instance, be used to feed a hydrogen powered car for about 9500 km.

Kinetic studies of ionic substituted copper catalysts for catalytic hydrogen combustion

Ionic substituted Cu catalysts in the reducible supports (SnO2, CeO2) and non-reducible supports (Al2O3, ZrO2) were synthesized by a single step solution combustion method and characterized by BET, XRD, TEM and XPS techniques. The catalytic activity of these compounds was investigated by performing the hydrogen combustion reaction. Due to the ionic substitution of aliovalent Cu ions, lattice oxygen was activated in these supports and all catalysts showed high rates and low activation energy. Cu substituted SnO2 catalyst showed the highest activity with 98% conversion at 320°C whereas Cu substituted ZrO2 was the least active among the studied catalysts with 98% conversion at 480°C. At 300°C, the rates of the reaction over Cu substituted SnO2 and Cu substituted ZrO2 were 8.7 and 1.94μmol/g/s. The reaction mechanisms were proposed based on an analysis of the surface mechanism and spectroscopic insights. The mechanism utilizing the oxide ion vacancies for O2 and H2 dissociation was proposed to describe the kinetics of the reaction over the reducible oxides SnO2 and CeO2. A mechanism based on the interaction of adsorbed H2 and O2 through the hydroxyl group was proposed for the reaction over non-reducible supports ZrO2 and Al2O3. These models were able to predict the rate of formation of H2O reasonably well.

Numerical Simulation on Catalytic Combustion of Hydrogen inside Micro Tube

Catalytic combustion of hydrogen/air mixture inside micro-tube was numerically investigated with detailed gas phase and surface catalytic chemical reaction mechanisms. Combustion characteristics for different reaction models, the influence of wall thermal conductivity, inlet velocity, and tube diameter on surface catalytic combustion reaction were discussed. The Computational results indicate that the surface catalytic combustion restrains the gas phase combustion. The higher wall temperature gradient for low wall thermal conductivity will promote the gas phase combustion shift upstream and will result in a higher temperature distribution. The micro-tube can be divided into two regions. The upstream region is dominated by the surface catalytic reaction and the downstream region is dominated by the gas phase combustion. With increasing inlet velocity, the region dominated by surface catalytic reactions expanded downstream and finally occupied the whole tube. The temperature of the flame core decreases with the decrease of tube diameter. Decreasing the tube diameter will enhance the surface catalytic reactions. Some theoretical evidences are provided for the application of catalytic combustion to Micro-electromechanical System (MEMS) and the extension of the combustion limits.