Combined steam and CO2 reforming of methane (CSCRM) over Ni–Pd/Al2O3 catalyst for syngas formation

In order to syngas formation, combined steam and carbon dioxide reforming of methane (CSCRM) used in the presence of Ni–Pd/Al₂O₃ catalysts, which were synthesized by the sol-gel method. Al₂O₃ supported Ni–Pd catalyst exhibited the appropriate surface area of 176.2 m²/g and high dispersion of NiO phase with an average crystallite size of 11 nm, which was detected on catalyst surface utilizing transmission electron microscopy (TEM). The influence of three independent operating parameters including reaction temperature in the range of 500–1000 °C; (CO₂ + H₂O)/CH₄ ratio, in the range of 1–3 and CO₂/H₂O ratio; in the range of 1–3, were investigated on the responses (i.e., CH₄ conversion, H₂ yield, CO yield, amount of coke formation on the catalyst surface and H₂/CO ratio) in CSCRM by using response surface methodology–central composite design (RSM-CCD) method. The obtained results from ANOVA and the proposed quadratic models could fine forecast the responses. It was seen that the total methane conversion and CO yield was almost accessible at temperatures higher than 850 °C. Moreover, the CO₂/H₂O ratio exhibited no significant effect on the CH₄ conversion, H₂ yield and CO yield of Ni–Pd/Al₂O₃ catalysts in CSCRM reaction. However, the high CO₂/H₂O ratio in inlet feed led to the syngas formation with a low H₂/CO ratio. The results revealed that lower CO₂/H₂O ratio and higher temperature as well as higher (CO₂ + H₂O)/CH₄ ratio help to decrease the coke formation.     

Autothermal syngas production from model gasoline over Ni,Rh and Ni–Rh/Al2O3 monolithic catalysts

On-board reforming of liquid fuels is attractive for fuel cell-powered auxiliary power units in vehicles. In this work, monometallic Ni/Al₂O₃/cordierite, Rh/Al₂O₃/cordierite and bimetallic Ni–Rh/Al₂O₃/cordierite monolithic catalysts were prepared, characterized and tested in ATR of isooctane for syngas production. Compared to monometallic formulations, the bimetallic Ni–Rh/Al₂O₃ catalyst was active for ATR at lower temperature and H₂ production already reached the equilibrium composition in 400–550 °C temperature range. The Ni–Rh/Al₂O₃ catalyst exhibited stable performances for 140 h in ATR of isooctane at 700 °C, and was unaffected by oxidizing conditions at 700 °C. Thermoneutral reactions conditions at H₂O/C = 2 were obtained with O/C = 0.66. Carbon deposition was marginal during ATR of isooctane and no carbons whiskers were detected. Post-reaction characterizations showed that the Ni particles were small enough to prevent filamentous carbon formation, while Rh also prevented carbon film deposition by improving the gasification of adsorbed C with steam.     

Hydrogen production from methane dry reforming over nickel-based nanocatalysts using surfactant-assisted or polyol method

In this study, two series of Ni-based nanocatalysts were synthesized successfully by the polyol and surfactant-assisted methods and subsequently tested for hydrogen production from CO₂–CH₄ reforming. Surfactant-assisted catalysts were prepared by using cetyl trimethyl ammonium bromide (CTAB) as a surfactant, whereas polyol catalysts were prepared in ethylene glycol (EG) medium with polyvinylpyrrolidone (PVP) as a nucleation-protective agent. The catalytic performance of each catalyst, in terms of H₂ yield and selectivity, was evaluated at different temperatures (500–800 °C). In order to clarify and explain the differences in catalytic activities of catalysts, the prepared samples were characterized by various techniques, such as BET, H₂-TPR, CO₂-TPD, XRD, TGA, SEM, HRTEM and CO pulse chemisorption. The results demonstrated that the method of preparation had a significant effect on the catalytic performance of tested catalysts. Overall, polyol catalysts showed high activity and selectivity for hydrogen production, while surfactant-assisted catalysts exhibited a fairly high resistance towards carbon deposition under similar reaction conditions of dry reforming of methane. Moreover, due to the reverse water gas shift reaction (RWGS), surfactant-assisted catalysts always produced smaller values of H₂/CO product ratio than their corresponding polyol catalysts.     

Effect of calcination conditions on time on-stream performance of Ni/La2O3–ZrO2 in low-temperature dry reforming of methane

A series of catalysts based on Ni supported on mesoporous La₂O₃–ZrO₂ was prepared and tested in low-temperature (400 °C) dry reforming of methane for 100 h on stream. The catalysts were obtained from the same precursor by calcining in either flowing air or Ar at different temperatures. Both the temperature and the atmosphere had an effect on the catalytic activity and on-stream stability. With increasing calcination temperature, the dispersion of Ni decreased. Surprisingly, this resulted not in the lower, but in the higher intrinsic activity of Ni species. This increase can be rationalized by assuming that the rate-determining step is not CH₄ decomposition, but the removal of carbon deposits from Ni particle by reaction with CO₂. The catalysts calcined at 800 °C in Ar and air showed the strongest and the second strongest deactivation, respectively, caused by the formation of crystalline carbon coatings due to a lower number of CO₂ adsorption sites. The size of Ni particles favoring the formation of layered carbon species was found to be the main origin of the catalysts deactivation in the low-temperature dry reforming of methane.     

H2 production by methane decomposition: Catalytic and technological aspects

Ni and Co supported on SiO₂ and Al₂O₃ silica cloth thin layer catalysts have been investigated in the catalytic decomposition of natural gas (CDNG) reaction. The influence of carrier nature and reaction temperature was evaluated with the aim to individuate the key factors affecting coke formation. Both Ni and Co silica supported catalysts, due to the low metal support interaction (MSI), promotes the formation of carbon filament with particles at tip. On the contrary, in case alumina was used as support, metals strongly interact with surface thus depressing both the metal sintering and the detachment of particles from catalyst surface. In such cases, carbon grows on metal particle with a “base mechanism” while particles remain well anchored on the catalyst surface. This allowed to realize a cyclic dual-step process based on methane decomposition and catalyst oxygen regeneration without deactivation of catalyst. Technological considerations have led to conclude that the implement of a process based on decomposition and regeneration of catalyst by oxidation requires the development of a robust catalytic system characterized by both a strong MSI and a well defined particle size distribution. In particular, the catalyst should be able to operate at high temperature, necessary to reach high methane conversion values (> 90%), avoiding at the same time the formation of both the carbon filaments with metal at tip or the encapsulating carbon which drastically deactivate the catalyst.     

Steam and auto-thermal reforming of bio-ethanol over MgO and Ni supported catalysts

Ethanol reforming over MgO and CeO₂ Ni supported catalysts in molten carbonate fuel cell (MCFC) simulated operative conditions has been investigated. Results revealed that an optimum O₂/C ratio (ATR condition) exists to enhance the performance of both catalysts which otherwise significantly deactivate mainly due to the coke formation. Oxygen contributes to depress coke formation but in some cases promotes acetaldehyde formation specially on Ni/CeO₂ catalysts. Very high H₂ selectivity (>98%) in steam reforming (SR) were obtained on both Ni/MgO and Ni/CeO₂ catalysts by operating at while in ATR conditions a decrease in hydrogen selectivity was observed at high GHSV only since reactions involved in the reaction mechanism are not at equilibrium.     

CO2 reforming of methane over Ni/ZnAl2O4 catalysts: Influence of Ce addition on activity and stability

The catalytic performance of Ni supported on Ce-promoted ZnAl₂O₄ was evaluated in methane dry reforming. The effect of different nominal loadings of cerium (3, 5 and 7 wt%) in the activity, product yield and stability was studied. Ce presented a promote effect in catalytic activity, product yield and especially in stability. However the catalytic performance was considerably influenced by the amount of cerium. SEM images presented smaller particles and TPR profiles revealed stronger active phase/support interaction by Ce addition which led to increasing methane conversion and decreasing coke deposition. Although high amount of Ce was not in favor of its promoting effect due to aggregation of CeO₂ on the catalyst surface. Among the catalysts investigated, the optimal catalytic activity and stability was achieved over the sample with 5 wt% of cerium.     

High-temperature electrolysis for large-scale hydrogen and syngas production from nuclear energy – summary of system simulation and economic analyses

A research and development program is under way at the Idaho National Laboratory (INL) to assess the technological and scale-up issues associated with the implementation of solid-oxide electrolysis cell technology for efficient high-temperature hydrogen production from steam. This work is supported by the US Department of Energy, Office of Nuclear Energy, under the Nuclear Hydrogen Initiative. This paper will provide an overview of large-scale system modeling results and economic analyses that have been completed to date. System analysis results have been obtained using the commercial code UniSim, augmented with a custom high-temperature electrolyzer module. Economic analysis results were based on the DOE H2A analysis methodology. The process flow diagrams for the system simulations include an advanced nuclear reactor as a source of high-temperature process heat, a power cycle and a coupled steam electrolysis loop. Several reactor types and power cycles have been considered, over a range of reactor outlet temperatures. Pure steam electrolysis for hydrogen production as well as coelectrolysis for syngas production from steam/carbon dioxide mixtures have both been considered. In addition, the feasibility of coupling the high-temperature electrolysis process to biomass and coal-based synthetic fuels production has been considered. These simulations demonstrate that the addition of supplementary nuclear hydrogen to synthetic fuels production from any carbon source minimizes emissions of carbon dioxide during the production process.     

Catalytic reforming of gasoline to hydrogen: Kinetic investigation of deactivation processes

Catalytic reforming of gasoline to a hydrogen-rich gas is a possible route to feed a fuel cell for electricity production on-board a vehicle. To properly design a fuel processor system, knowledge about the kinetics of the different reactions involved in the reforming is needed. Kinetic studies are hampered by the fact that sulfur compounds present in commercial gasoline may lead to a progressive deactivation of the catalyst. We have undertaken such a study with an optically accessible catalytic channel flow reactor enabling concentration profiles and catalyst surface temperatures to be measured. The concentration profiles measured at different times on stream revealed a progressive deactivation of the catalyst. Isothermal reaction rate constants, depending on the time on stream, were derived by fitting a Langmuir–Hinshelwood kinetic model to the experimental species concentration profiles. The modeling results indicated that the steam reforming of higher hydrocarbons was more strongly affected by the presence of sulfur in the feed than the water gas shift reaction and the steam reforming of methane. Carbon formation was inferred from changes in surface emissivity during the experiments. It is suggested that the primary reason for the observed deactivation is due to the presence of sulfur compounds in the feed. The deactivated catalyst would then promote the formation of coke at the surface, i.e. coke formation is probably a consequence of the deactivation and not a cause for it. Although the variability in preparing the coated catalytic plates affected the measured kinetic rate parameters, the observed trends were in general consistent for all runs.     

Design of a novel hydrogen–syngas catalytic mesh combustor

A small-scale wire-mesh catalytic combustor is developed and evaluated for hydrogen–syngas combustion in domestic power/heating generator. The single- and double-layer wire-mesh catalysts are tested to verify their performance on CO conversions. Experimental results indicate that the double-layer wire-mesh catalytic combustor yields a higher CO conversion ratio (>90%) than that (<40%) of the single-layer wire-mesh catalyst in the range of fuel concentrations, fuel compositions, and flow velocities studied. In order to maintain a stable heterogeneous/homogeneous reaction at the second stage of wire-mesh catalyst, a minimum of 4% hydrogen in syngas and at least 200 °C of preheating temperature on the second wire-mesh catalyst are suggested. The advantages of the wire-mesh combustor are its compactness and ease of assembly and cleaning.     

Hydrogen and syngas yield from residual branches of oil palm tree using steam gasification

Wastes produced during oil palm production from agro-industries have great potential as a source of renewable energy in agriculturally rich countries, such as Thailand and Malaysia. Clean chemical energy recovery from oil palm residual branches via steam gasification is investigated here. A semi-batch reactor was used to investigate the gasification of palm trunk wastes at different reactor temperatures in the range of 600 to 1000 °C. The steam flow rate was fixed at 3.10 g/min. Characteristics and overall yield of syngas properties are presented and discussed. Results show that gasification temperature slightly affects the overall syngas yield. However, the chemical composition of the syngas varied tremendously with the reactor temperature. Consequently, the syngas heating value and ratio of energy yield to energy consumed were found to be strongly dependent on the reactor temperature. Both the heating value and energy yield ratio increased with increase in reactor temperature. Gasification duration and the steam to solid fuel ratio indicate that reaction rate becomes progressively slower at reactor temperatures of less than 700 °C. The results reveal that steam gasification of oil palm residues should not be carried out at reactor temperatures lower than 700 °C, since a large amount of steam is consumed per unit mass of the sample in order to gasify the residual char.     

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.     

Effects of hydrogen addition on structure and NO formation of highly CO-Rich syngas counterflow nonpremixed flames under MILD combustion regime

The present study has numerically investigated the Moderate or Intense Low oxygen Dilution (MILD) combustion regime, combustion processes and NO formation characteristics of the highly CO-rich syngas counterflow nonpremixed flames. To realistically predict the flame properties of the highly CO-rich syngas, the chemistry is represented by the modified GRI 3.0 mechanism. Computations are performed to precisely analyze the flame structure, NO formation rate, and EINO of each NO sub-mechanism. Numerical results reveal that the hydrogen enrichment and oxygen augmentation substantially influence the NO emission characteristics and the dominant NO production route in the CO-rich syngas nonpremixed flames under MILD and high temperature combustion regimes. It is found that the most dominant NO production routes are the NNH path for the lowest oxygen level (3%) and the thermal mechanism for the highest O₂ condition (21%). For the intermediate oxygen level (9%), the most dominant NO production routes are the NNH route for the hydrogen fraction up to 5%, the CO₂ path for the hydrogen fraction range from 5% to 10% and the thermal mechanism for the hydrogen fraction higher than 10%, respectively. To evaluate the contribution of the specific reaction on EINO the sensitivity coefficients are precisely analyzed for NO formation processes with the dominance of NNH/CO₂/Thermal mechanism under the highly CO-rich syngas flames.     

Hydrogen and aromatic production by means of a novel membrane integrated cross flow CCR naphtha reforming process

In this study a new configuration i.e. membrane reactor with Pd/Ag membrane was proposed for catalytic naphtha reforming, and examined through mathematical modeling considering catalyst deactivation. According to complex kinetic of reforming process a new kinetic model including 32 pseudo components with 84 reactions is proposed. Mathematical modeling of this process in continuous catalyst regeneration mode of operation is accomplished in two dimensions (radial and axial) by considering cross flow pattern. To validate the competence of the conventional configuration model, its results are compared with the industrial data. Aromatics and hydrogen production were boosted as a result of hydrogen removal in AMR while light end production was diminished as a consequence of hydrogen separation and higher temperature drop in AMR.