Hydrogen production by catalytic partial oxidation of methane and propane on Ni and Pt catalysts

In recent years the catalytic partial oxidation has been taken into consideration as a suitable process for hydrogen production, because of its exothermic nature which makes the process less energy and capital cost intensive with respect to steam reforming. In this paper the behaviour of three different catalyst typologies, two based on Ni–_Al2O3${\mathrm{Al}}_2{\mathrm{O}}_3$ (different in active phase composition) and one constituted by Pt supported on _CeO2${\mathrm{CeO}}_2$, is studied for partial oxidation of propane (as representative of liquefied petroleum gas). For comparison the same catalysts have been tested also in methane partial oxidation.     

Catalytic partial oxidation of methane over nanosized Rh supported on Fecralloy foams

Structured catalysts for the partial oxidation of methane were prepared by supporting Rh nanoparticles onto Fecralloy foams at relatively low precious metal loadings. The investigation was focused mainly on an innovative and straightforward preparation procedure consisting in the direct cathodic electrodeposition of Rh onto foam samples. For the sake of comparison, other Rh-based catalysts were prepared with a more traditional approach, by using the same foams and an AlPO₄ washcoat layer. The catalysts were characterized by SEM-EDS, XRD and cyclic voltammetry, to assess the Rh surface area, and tested in the CPO of methane to syngas under self-sustained high temperature conditions at short-contact-time. During prolonged CPO tests the performance of electrochemically prepared catalysts underwent a progressive decline, as compared to stable operation of AlPO₄ washcoated catalysts, which was mainly ascribed to sintering of Rh nanoparticles, negatively affecting the activity for methane steam reforming.     

Hydrogen production by coupled catalytic partial oxidation and steam methane reforming at elevated pressure and temperature

Hydrogen production by coupled catalytic partial oxidation (CPO) and steam methane reforming of methane (OSMR) at industrial conditions (high temperatures and pressures) have been studied over supported 1 wt.% NiB catalysts. Mixture of air/CH₄/H₂O was applied as the feed. The effects of O₂:CH₄ ratio, H₂O:CH₄ ratio and the gas hourly space velocity (GHSV) on oxy-steam reforming (OSRM) were also studied. Results indicate that CH₄ conversion increases significantly with increasing O₂:CH₄ or H₂O:CH₄ ratio. However, the hydrogen mole fraction goes through a maximum, depending on reaction conditions, e.g., pressure, temperature and the feed gases ratios. Carbon deposition on the catalysts has been greatly decreased after steam addition. The supported 1 wt.% NiB catalysts exhibit high stability with 85% methane conversion at 15 bar and 800 °C during 70 h time-on-stream reaction (CH₄:O₂:H₂O:N₂ = 1:0.5:1:1.887). The thermal efficiency was increased from 35.8% by CPO (without steam) to 55.6%. The presented data would be useful references for further design of enlarged scale hydrogen production system.     

Hydrogen production by partial oxidation of ethanol over Pt/CNT catalysts

The platinum‐supported catalysts have been prepared by ethylene glycol reduction method, and the catalysts were applied to the partial oxidation of ethanol (POE) for hydrogen production. Four types of support, including CNTs, Al₂O₃, ZrO₂, and CeO₂, were used on POE catalytic performance test. Prior to catalyst preparation, the influence of acidic pretreatment on CNTs purity, surface morphology, and pore structure were investigated. The acid‐treated CNTs and prepared catalysts were characterized with N₂ physisorption, Raman, thermogravimetric, and transmission electron microscopy analysis. The experimental results show that the particle size and metal dispersion of platinum on CNTs, as well as POE activity, depend on pH value of reducing agent and reduction temperature in the stage of catalyst preparation. In the condition pH value of 10 and temperature at 120 °C for catalyst 5 wt% Pt/CNTs preparation, 2 nm platinum clusters were obtained. Using the as‐prepared catalyst to study the effects of POE reaction conditions on the ethanol conversion, hydrogen selectivity, and hydrogen production rate under constant gas hourly space velocity, the corresponding values at the optimum reaction temperature 400 °C and O₂/C₂H₅OH molar ratio of 0.5 were 98.2%, 97.5%, and 202.3 mmol s^?1 kg^?1, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Simulation of a fuel reforming system based on catalytic partial oxidation

Catalytic partial oxidation (CPO) has potential for producing hydrogen that can be fed to a fuel cell for portable power generation. In order to be used for this purpose, catalytic partial oxidation must be combined with other processes, such as water-gas shift and preferential oxidation, to produce hydrogen with minimal carbon monoxide. This paper evaluates the use of catalytic partial oxidation in an integrated system for conversion of a military logistic fuel, JP-8, to high-purity hydrogen. A fuel processing system using CPO as the first processing step is simulated to understand the trade-offs involved in using CPO. The effects of water flow rate, CPO reactor temperature, carbon to oxygen ratio in the CPO reactor, temperature of preferential oxidation, oxygen to carbon ratio in the preferential oxidation reactor, and temperature for the water-gas shift reaction are evaluated. The possibility of recycling water from the fuel cell for use in fuel processing is evaluated. Finally, heat integration options are explored. A process efficiency, defined as the ratio of the lower heating value of hydrogen to that of JP-8, of around 53% is possible with a carbon to oxygen ratio of 0.7. Higher efficiencies are possible (up to 71%) when higher C/O ratios are used, provided that olefin production can be minimized in the CPO reactor.     

Effect of support on catalytic properties of Rh catalysts for steam reforming of 2-propanol

Catalytic performance of Rh catalyst supported on CeO₂, Al₂O₃, SiO₂, ZrO₂, MgO or TiO₂ for steam reforming of 2-propanol has been studied. The performance was greatly influenced by the type of the supports through interactions between Rh and supports. CeO₂-supported Rh catalyst resulted in the highest selectivity among the catalysts studied here. It probably has a longer catalytic life than Al₂O₃-supported catalysts actually known to be stable, because the amount of coke deposited on it was much smaller than that on the Al₂O₃-supported one. This mitigation of coke deposition has been explained by a reduction and oxidation cycle of CeO₂.     

Production of synthesis gas by partial oxidation and steam reforming of biomass pyrolysis oils

As the lowest cost biomass-derived liquids, pyrolysis oils (also called bio-oils) represent a promising vector for biomass to fuels conversion. However, bio-oils require upgrading to interface with existing infrastructure. A potential pathway for producing fuels from pyrolysis oils proceeds through gasification, the conversion to synthesis gas. In this work, the conversion of bio-oils to syngas via catalytic partial oxidation over Rh–Ce is evaluated using two reactor configurations. In one instance, pyrolysis oils are oxidized in excess steam in a freeboard and passed over the catalyst in a second zone. In the second instance, bio-oils are introduced directly to the catalyst. Coke formation is avoided in both configurations due to rapid oxidation. H₂ and CO can be produced autothermally over Rh–Ce catalysts with millisecond contact times. Co-processing of bio-oil with methane or methanol improved the reactor operation stability.     

Entropy generation from hydrogen production of catalytic partial oxidation of methane with excess enthalpy recovery

Catalytic partial oxidation of methane (CPOM) is an important route for producing hydrogen and it is featured by autothermal reaction. To recognize the reaction characteristics of CPOM, H₂ production and entropy generation from CPOM in Swiss-roll reactors are studied numerically. The considered parameters affecting the performance of CPOM include the excess enthalpy recovery, gas hourly space velocity (GHSV), number of turns and atomic O/C ratio. The impact of chemical reactions, heat transfer and friction on entropy generation is also analyzed. The results indicate that preheating reactants through waste heat recovery as well as increasing GHSV or number of turns is conducive to enhancing H₂ yield, whereas the maximum H₂ yield develops at O/C = 1.2. A higher H₂ yield is always accompanied by a higher value of entropy generation, and chemical reactions are the main source of entropy generation, especially from steam methane reforming. In contrast, viscous dissipation almost plays no part on entropy generation, compared to heat transfer and chemical reactions. From the analysis of entropy generation, detailed mechanisms of H₂ production from CPOM can be figured out.     

Enhancement effect of heat recovery on hydrogen production from catalytic partial oxidation of methane

The effect of heat recovery on hydrogen production from catalytic partial oxidation of methane (CPOM) and its reaction characteristics in a reactor are investigated using numerical simulations. The reactor is featured by a Swiss-roll structure in which a rhodium (Rh) catalyst bed is embedded at the center of the reactor. By recovering the waste heat from the product gas to preheat the reactants, it is found that the combustion, steam reforming and dry reforming of methane in the catalyst bed are enhanced to a great extent. As a result, the methane conversion and hydrogen yield are improved more than 10%. Considering the operation conditions, a high performance of hydrogen production from CPOM can be achieved if the number of turns in the reactor is increased or the gas hourly space velocity (GHSV) of the reactants in the catalyst bed is lower. However, with the condition of heat recovery, the flow direction of the reactants in the reactor almost plays no part in affecting the performance of CPOM. In summary, the predictions reveal that the reactor with a Swiss-roll structure can be applied for implementing CPOM with high yield of hydrogen.     

Transient reaction and exergy analysis of catalytic partial oxidation of methane in a Swiss-roll reactor for hydrogen production

Catalytic partial oxidation of methane (CPOM) is a promising method for hydrogen production with autothermal reaction. To figure out the unsteady reaction characteristics of CPOM in a Swiss-roll reactor along with heat recirculation, a numerical method is employed to simulate the transient reaction dynamics, with emphasis on energy recovery using exergy analysis. Three different gas hourly space velocities (GHSVs) of 5000, 10,000 and 50,000 h⁻¹ with the condition of atomic O/C ratio of 1 are considered. The predictions indicate that increasing GHSV substantially shortens the transient period of chemical reactions; however, it also reduces the methane conversion, as results of more reactants sent into the reactor and shorter residence time of the reactants in the catalyst bed. Within the investigated range of GHSV, the methane conversion with energy recovery at the steady state is larger than 80%, much higher than the reaction without heat recovery. The selectivities of H₂ and CO in the product gas are always larger than 90%. The exergy recovery is in the range of 66–80%, implying that over two-third useful work contained in the product gas can be reused to preheat the reactants in the reactor, thereby enhancing the performance of CPOM.     

Production of hydrogen for fuel cells by catalytic partial oxidation of ethanol over structured Ni catalysts

Cordierite monoliths, ceramic foams made from mullite and zirconia–alumina as well as γ-Al₂O₃ pellets were employed as supports for Ni/La₂O₃ structured catalysts for the production of hydrogen by catalytic partial oxidation of ethanol. Although all catalysts were very active for ethanol conversion and very selective towards the desired products, the one supported on the zirconia–alumina ceramic foam produced slightly better results. Tested under a wide variety of process conditions, the catalyst supported on the monolith exhibited excellent catalytic performance and long-term stability. In addition to this catalyst, which was prepared by washcoating the active phase on the support, catalysts were prepared on monoliths by adsorption and sol–gel techniques. Adsorption from solutions produced the catalyst with the weakest performance while the sol–gel method resulted in a catalyst with intriguing behavior. Overall, catalysts produced by washcoating on cordierite monoliths are the most promising candidates for the production of hydrogen by partial oxidation of ethanol. Other supports and preparation methods have the potential to produce better catalytic materials but require further optimization.     

Hydrogen production from catalytic steam reforming of glycerol over various supported nickel catalysts

Supported Ni catalysts have been investigated for hydrogen production from steam reforming of glycerol. Ni loaded on Al₂O₃, La₂O₃, ZrO₂, SiO₂ and MgO were prepared by the wet-impregnation method. The catalysts were characterized by nitrogen adsorption–desorption, X-ray diffraction and scanning electron microscopy. The characterization results revealed that large surface area, high dispersion of active phase on support, and small crystalline sizes are attributes of active catalyst in steam reforming of glycerol to hydrogen. Also, higher basicity of catalyst can limit the carbon deposition and enhance the catalyst stability. Consequently, Ni/Al₂O₃ exhibited the highest H₂ selectivity (71.8%) due to small Al₂O₃ crystallites and large surface area. Response Surface Methodology (RSM) could accurately predict the experimental results with R-square = 0.868 with only 4.5% error. The highest H₂ selectivity of 86.0% was achieved at optimum conditions: temperature = 692 °C, feed flow rate = 1 ml/min, and water glycerol molar ratio (WGMR) 9.5:1. Also, the optimization results revealed WGMR imparted the greatest effect on H₂ selectivity among the reaction parameters.     

Hysteresis and reaction characterization of methane catalytic partial oxidation on rhodium catalyst

Hysteresis effects and reaction characteristics of methane catalytic partial oxidation (CPO) in a fixed-bed reactor are numerically simulated. The reactions are modeled based on the experimental measurements of methane CPO with a rhodium (Rh) catalyst. Three C/O ratios of 0.6, 1.0 and 1.4 are considered in the study. When the Reynolds number is 200, the predictions indicate that the methane CPO is always triggered at around the inlet temperature of 550 K, regardless of what the C/O ratio is. It is of interest that if the inlet temperature is decreased after the methane CPO develops at higher inlet temperatures, the reversed path of methane conversion is different from the original path at lower inlet temperatures. The hysteresis effect of the methane CPO is thus observed. The hysteresis behavior implies that a higher yield of syngas or hydrogen can be achieved by controlling the reaction process. Decreasing the C/O ratio intensifies the methane CPO so that the hysteresis effect is more pronounced, and vice versa. An increase in Reynolds number delays the excitation temperature of methane CPO and lessens the hysteresis effect of methane conversion due to the growth of fluid inertial force. However, the hysteresis effect of the maximum temperature in the catalyst bed increases as a result of more methane consumption.     

On-line estimation of inlet and outlet composition in catalytic partial oxidation

An estimation strategy is presented for determining inlet and outlet composition of catalytic partial oxidation (CPOX) of methane over rhodium catalyst using simple, fast measurements: temperature, and thermal conductivity. A 1-D high fidelity simulation model for CPOX studied in Ref. [1] for a portable fuel cell application is developed and enhanced for transient experiments. Process dynamics are analysed to demonstrate how solid temperatures along the axes of the reactor reflect the endothermic/exothermic interplay of reactions during a process upset. Model reduction is then used to obtain a low complexity model suitable for use in a moving horizon estimator with update rates faster than 0.02 s. System theoretic observability analysis is then conducted to predict the suitability of different measurement designs and the best locations for temperature measurements for estimating both inlet and outlet gas mole fractions for all species. Finally, a Moving Horizon estimator is implemented and simulation experiments are conducted to verify the accuracy of the estimator.     

Kinetics of catalytic oxidation of methane,ethane and propane over palladium oxide

Catalytic oxidation of methane, ethane and propane over a palladium oxide (PdO) surface was investigated experimentally by wire microcalorimetry. The oxidation rate was determined for each reactant at atmospheric pressure in the temperature range of 600–800 K. The apparent kinetic parameters were extracted from the experimental measurements. It is shown that the oxidation of these hydrocarbons over the PdO surface proceeds with a similar mechanism: they undergo dissociative adsorption followed by the conversion of surface fragments to final products. A detailed surface reaction model is proposed, and the kinetic parameters of the crucial reactions are deduced from the present experimental observations. The catalytic oxidation rates are found to increase in the order of methane, ethane and propane. This observation is consistent with density functional theory calculations and may be correlated with the C–H bond energies of the corresponding surface intermediates.     

Enhancement of heat recirculation on the hysteresis effect of catalytic partial oxidation of methane

The hysteresis characteristics of catalytic partial oxidation of methane (CPOM) in a Swiss-roll reactor are predicted numerically by varying Damköhler number. Particular attention is paid to the influences of heat recirculation, gas hourly space velocity (GHSV), and atomic O/C ratio on the hysteresis loop and performance of CPOM. The reactions of methane combustion, steam reforming, and CO₂ or dry reforming are simultaneously considered. The results reveal that preheating reactants through excess enthalpy recovery is conducive to the ignition of CPOM and extending its extinction limit, so the ignition and extinction Damköhler numbers are lowered. The analysis also suggests that steam reforming is more sensitive to the heat recovery than methane combustion and dry reforming. An increase in GHSV reduces the residence time of reactants in the catalyst bed, thereby enlarging the ignition and extinction Damköhler numbers of CPOM. A higher O/C ratio facilitates the ignition of CPOM, stemming from more oxygen supplied, but the ratio should be controlled below 1.2. From the hysteresis phenomena, hydrogen can be produced from methane at a lower Damköhler number to save more energy for performing CPOM.     

Lanthanide modified Pt/CeO2-based catalysts for methane partial oxidation: Relationship between catalytic activity and structure

In most cases, reasonable design and construction of Pt/CeO₂-based catalysts and detailed exploration of relationship between its structural characteristics and the catalytic activity are crucial to improve the catalytic performance and reduce the cost. In this work, a series of CeO₂ doped with lanthanide metal ions (La, Nd, Er and Yb) has been successfully synthesized, and then Pt is introduced through impregnation. The morphology, structure and component analysis are characterized by SEM, TEM (HRTEM), EDS, XRD, ICP-AES, XPS, UV Raman, O₂-TPD, H₂-TPR and CO or O₂-pulse chemisorption, and the corresponding catalytic performances are developed by partial oxidation of methane. On the basis of the analysis of the structural properties of various catalysts, it is found that the Pt/CeLa catalyst shows the best catalytic performance due to its low valence state of Pt, excellent oxygen migration capacity and oxygen storage capacity, T₅₀ is 510 °C and the selectivity is superiority. What's more, the modification of CeO₂ by lanthanide metal ions especially La³⁺ can effectively change the oxygen activity of supports, so that this catalyst can be used in various redox catalytic reactions.     

Hysteresis loops of methane catalytic partial oxidation for hydrogen production under the effects of varied Reynolds number and Damköhler number

Hysteresis loops of catalytic partial oxidation of methane (CPOM) for hydrogen production under the effects of varied Reynolds number and Damköhler number are investigated numerically in this study. The physical phenomena are predicted using the indirect mechanism, which consists of the total oxidation (or combustion), steam reforming and CO₂ reforming of methane in a catalyst bed. Numerical results reveal that, when the Damköhler number is relatively low, a hysteresis loop of CPOM from varying Reynolds number develops. Increasing the Damköhler number leads to the loop shifting toward the regime of high Reynolds number. However, once the Damköhler number is large to a certain extent, the chemical reactions are always exhibited for the Reynolds number less than 2000. A closed loop is thus not observed. Alternatively, for a given Reynolds number, an ignited Damköhler number and an extinguished Damköhler number can be obtained. Accordingly, three different regions in the plot of Damköhler number versus Reynolds number are identified. Physically, when the role played by Damköhler number on CPOM is much more important than by the Reynolds number (Region I), the thermal effect governs the chemical reactions. In contrast, if the Reynolds number plays a key role in determining the CPOM (Region III), the chemically frozen flow prevails over the catalyst bed. When the residence times of the total oxidation and convection in the catalyst bed are in an equivalent state (Region II), CPOM is characterized by a dual-solution, rendering the hysteresis loops. From the distributions of ignited and extinguished Damköhler numbers, the catalytic reactor and operation of partial oxidation of methane and other fuels can be designed accordingly.     

Hydrogen production from methane under the interaction of catalytic partial oxidation,water gas shift reaction and heat recovery

Hydrogen production from the combination of catalytic partial oxidation of methane (CPOM) and water gas shift reaction (WGSR), viz. the two-stage reaction, in a Swiss-roll reactor is investigated numerically. Particular emphasis is placed on the interaction among the reaction of CPOM, the cooling effect due to steam injection and the excess enthalpy recovery with heat recirculation. A rhodium (Rh) catalyst bed sitting at the center of the reactor is used to trigger CPOM, and two different WGSRs, with the aids of a high-temperature (Fe–Cr-based) shift catalyst and a low-temperature (Cu–Zn-based) shift catalyst, are excited. Two important parameters, including the oxygen/methane (O/C) ratio and the steam/methane (S/C) ratio, affecting the efficiencies of methane conversion and hydrogen production are taken into account. The predictions indicate that the O/C ratio of 1.2 provides the best production of H₂ from the two-stage reaction. For a fixed O/C ratio, the H₂ yield is relatively low at a lower S/C ratio, stemming from the lower performance of WGSR, even though the cooling effect of steam is lower. On the contrary, the cooling effect becomes pronounced as the S/C ratio is high to a certain extent and the lessened CPOM leads to a lower H₂ yield. As a result, with the condition of gas hourly space velocity (GHSV) of 10,000 h⁻¹, the optimal operation for hydrogen production in the Swiss-roll reactor is suggested at O/C = 1.2 and S/C = 4–6.     

Conical-shaped foam reactors for catalytic partial oxidation applications

The role of the reactor geometry for catalytic partial oxidation of methane is numerically investigated to improve catalyst thermal stability and at the same time to achieve high fuel conversion and reforming efficiency. The performance of cylindrical-shaped foam monolith reactors is compared with that of conical-shaped foam monolith reactors. A quasi-1D heterogeneous mathematical model was developed to account for a variable reactor cross-sectional area and for a variety of chemical and transport steps. Radiative heat transfer within the cellular structure was properly accounted for with the zone method. The results suggest that converging conical-shaped reactors allow a significant decrease of the maximum surface temperatures and high reforming performance.