Syngas Selectivity Research Articles

Chemical looping partial oxidation of methane with CO2 utilization on the ceria-enhanced mesoporous Fe2O3 oxygen carrier

The high-purity syngas production with a molar ratio of H2 to CO equal to 2 was achieved through a chemical looping process with a CH4-CO2 feed mixture on a ceria-enhanced mesoporous Fe2O3/Al2O3 oxygen carrier. The presence of CO2 in the mixture feed enables the H2/CO ratio to be maintained as 2 desirable for the syngas-to-liquid hydrocarbon process by suppressing the methane decomposition even when the amount of reducible oxygen carrier was sufficiently small. By incorporating a small amount of CeO2 (molar Ce/Fe ratio = 0.15) to the iron oxide mesoporous oxygen carrier by the sol-gel method, the syngas selectivity also increased although the amount of reducible oxygen was large enough to cause the total combustion. Due to the co-feeding of CO2 with CH4 and the textural property of the ceria-enhanced Fe2O3/Al2O3 mesoporous oxygen carrier, the enhanced redox activity for the chemical looping process was demonstrated under the CO2/CH4 feed ratio of 0.28 with the redox performance of CH4 conversion = 93.11%, CO selectivity = 93.23%, average carbon deposit = 0.048 molC/molsyngas, and average H2/CO ratio = 2.04. The fluctuation of the H2/CO ratio with the reaction time was minimized by adjusting the real-time CO2/CH4 feed ratio and then, the consistent syngas production was realized even in the fixed bed chemical looping process.

Simulation and optimization of reforming reactors for carbon dioxide utilization using both rigorous and reduced models

CO2 is a major greenhouse gas emitted at the global scale from burning fossil fuels. Converting CO2 to chemicals such as syngas is a promising way to reduce CO2 emissions from stationary sources. In this work, we explore technologies for the thermochemical conversion of CO2 to syngas using both rigorous and reduced order reactor models. Specifically, we study the CO2 utilization potentials of primary reforming such as dry reforming (DR), steam methane reforming (SMR) and partial oxidation (POX), and combined reforming such as combined dry and steam methane reforming (CDSMR), auto-thermal reforming (ATR), combined partial oxidation and dry reforming (PODR) and tri-reforming (TR). Through detailed simulation and analysis, we show the importance of considering rigorous models for accurate prediction. We also develop algebraic surrogate models for reactor outlets as functions of reactor design and operating conditions. The replacement of the high-fidelity models with their simpler algebraic surrogates provides an efficient way for superstructure-based reactor synthesis. Using a mixed-integer nonlinear optimization (MINLP)-based reactor synthesis model, the reactors are further optimized for maximizing CO2 utilization and syngas selectivity. PODR has been found to have the highest potential for converting CO2 for the range of syngas ratios (H2/CO) between 1 and 1.7, achieving almost 100% CO2 conversion with a syngas selectivity ranging 80–93%. We further improve the conversion and syngas selectivity by distributing the feeds to multiple reformers. A combination of DR, CDSMR and TR achieves the best CO2 conversion for syngas ratios up to 2.4. For higher syngas ratios, a combination of SMR, TR and RWGS are found to be optimal. These are non-intuitive results that need further attention.

Enhanced Lattice Oxygen Reactivity over Ni-Modified WO3-Based Redox Catalysts for Chemical Looping Partial Oxidation of Methane

Partially oxidizing methane into syngas via a two-step chemical looping scheme is a promising option for methane transformation. Providing the optimum lattice oxygen to selectively produce syngas represents the major challenge for the development of oxygen carrier materials in chemical looping processes. This paper describes the design of WO3-based oxygen carriers as the primary source of lattice oxygen with high melting points and attractive syngas selectivity. To further enhance the lattice oxygen availability and methane conversion capacity, NiO nanoclusters are introduced, considering the doping effect on chemical bonding disruption in both bulk and surface regions. For Ni0.5WOx/Al2O3, the nickel cations incorporated into the bulk of WO3 can strongly weaken the tungsten–oxygen bond strength and increase the availability of lattice oxygen. The surface-grafted nickel species can effectively activate methane molecules and catalyze the partial oxidation reaction. Total methane conversion and syngas yield ...

Preparation and application of nickel based carbon fibers for the steam reforming of methane

The steam and KOH activation methods were used to activate lignin based carbon fibers. The original and activated carbon fibers were applied to prepare three kinds of nickel based catalysts. The characterization results illustrated that the KOH activated carbon fibers (KACF) possessed the best surface structural parameters. The tests for catalytic performance showed that the catalyst supported on the KACF was the greatest in the steam reforming of methane. Based on that, the catalysts with different metal content were prepared to obtain an optimal content, which possessed the greatest catalytic activity. The catalyst of 5% metal content supported on the KACF was proved to have the highest methane conversion rate and syngas selectivity. And the optimal catalyst was applied for the steam reforming of methane. The CH4 conversion ratio could reach more than 90%. The influence of catalyst dosage, reaction temperature and the molar ratio of H2O/CH4 was investigated. The results indicated that the ratio of hydrogen to carbon monoxide could be adjusted by the temperature and the ratio of H2O/CH4. Higher temperatures could increase the ratio of H2/CO, while the excess steam decreased it. Besides, the carbon deposition experiment of methane decomposition with the catalysts of 5% Ni/SKACF and 5% Ni/γ-Al2O3 proved that the catalyst prepared by carbon fiber support has great properties for carbon deposition resistance.

Synthesis gas production via the solar partial oxidation of methane-ceria redox cycle: Conversion, selectivity, and efficiency

The importance of methane conversion, syngas selectivity, and oxidizer conversion for efficient syngas production by the partial oxidation of methane using a metal oxide redox cycle is quantified. The operating conditions which enable high conversion of methane to syngas over cerium oxide and conversion of carbon dioxide to carbon monoxide in the subsequent oxidation reaction are identified experimentally. The parametric study considers operating temperatures of 900 and 1000 °C and methane flow rates from 1 to 15 mL min−1 g−1 in a fixed bed of porous ceria particles. The reduced ceria is reoxidized in a flow of 10 mL min−1 g−1 CO2 to produce CO. A trade-off of achieving high methane conversion is observed. For example, at 1000 °C, the cycle-averaged methane conversion increases from 13% for reduction in 15 mL min−1 g−1 to 60% in 1 mL min−1 g−1. For the same change in methane flow rate, the cycle-averaged selectivities decrease from 78% to 39% (CO) and 77% to 40% (H2) and the oxidizer conversion decreases from 93% to 48%. The maximum projected solar-to-fuel thermal efficiency is 27% for cycling at 1000 °C with reduction in 5 mL min−1 g−1 methane.

Theoretical and experimental study of methane partial oxidation to syngas in catalytic membrane reactor with asymmetric oxygen-permeable membrane

This paper presents results of theoretical and experimental research concerning synthesis of multilayer asymmetric oxygen-permeable membrane and its application for partial oxidation of methane. The membrane is based on macroporous Ni-Al foam substrate with three layers of perovskite-fluorite nanocomposites with graded (meso-micro) porosity, thin dense MnFe2O4–Ce0.9Gd0.1O2 layer and porous layer of LaNi0.9Pt0.1O3/Pr0.3Ce0.35Zr0.35O2-x catalyst. Testing of membrane in methane partial oxidation process demonstrates a good and stable performance.The mathematical modeling of the methane partial oxidation process in the catalytic membrane reactor has been provided. The developed model was applied to find the process (temperature, gas flow rates, etc.) and membrane (pore diameter of porous layer, thickness of porous layer) parameters corresponding to highest methane conversion and syngas selectivity.

Impact of sulfur on catalytic partial oxidation of jet fuel surrogates over Rh/Al2O3

Jet-fuel surrogates with varying composition and sulfur content were partially oxidized over a Rh/Al2O3 honeycomb catalyst. The surrogates consisted of a blend of n-dodecane, 1,2,4-trimethylbenzene, and benzothiophene to represent model mixtures of the main chemical properties of jet fuels. The experiments were performed under quasi-autothermal conditions for three different C/O-ratios in a set-up, specifically designed for fuels with high boiling points. The product distribution significantly changes with sulfur addition showing increased water formation, undesired by-products and a decline in fuel conversion. A steady increase of by-product formation over time on stream leads to coke deposition for fuels with ≥50 mg S per kg fuel. The interplay between sulfur and coke, caused deactivation and its impact on syngas selectivity, fuel conversion, and by-product formation is discussed.

A novel LaGa0.65Mg0.15Ni0.20O3–δ perovskite catalyst with high performance for the partial oxidation of methane to syngas

A novel perovskite catalyst with the composition of LaGa0.65Mg0.15Ni0.20O3–δ (LGMN) is synthesized by the sol–gel combustion technique. The nanostructure catalyst has been examined for the partial oxidation of methane (POM) into syngas. A variety of characterizations including XRD, BET, SEM and TG–DTA were applied to determine the crystalline structure of the formed nanosized particles. The syngas selectivity over the catalyst may reach up to 100% with the methane conversions larger than 81% at 900°C and 55mLmin−1g−1 feed velocity. XRD and thermal analysis reveals that the LGMN powder has maintained the perovskite structure very well after 210h POM reaction signaling its high chemical stability.

Partial oxidation of methane on Rh/ZrO2 and Rh/Ce–ZrO2 on monoliths: Catalyst restructuring at reaction conditions

0.5% Rh catalysts on ZrO2 or CeO2–ZrO2, coated on monoliths were tested for partial oxidation of methane, (GHSV=100000h−1). We ran temperature cycles up to 850°C, varying the O2/CH4 ratio from 0.5 to 0.7. The catalysts were characterized by XRD, TPR/TPO, BET and chemisorption. ZrO2 required a long conditioning step, to reach stable performance, while the CeO2–ZrO2 catalyst quickly gained steady activity. The conditioning step is explained with a restructuring of the surface, with the metallic particles becoming smaller. Ceria lowers the ignition temperature by 60°C. At low temperature, ceria allows an increase in CH4 conversion and selectivity to syngas. At high temperature, the CeO2–ZrO2 catalyst significantly increases the CH4 conversion, compared to ZrO2, approaching 100%. However, the selectivity to syngas decreases below 80%. The syngas selectivity is higher at lower O2/CH4 ratio, at any temperature, but the absolute amount of syngas can be larger with more O2.

Fe-based Fischer Tropsch synthesis of biomass-derived syngas: Effect of synthesis method

Two 100Fe/4Cu/4K/6Zn catalysts were prepared using two different methods: coprecipitation or impregnation methods. The effect of the preparation methods on the catalyst structure, catalytic properties, and the conversion of biomass-derived syngas via Fischer–Tropsch synthesis was investigated. Syngas was derived from gasifying Southern pine woodchips and had the composition of 3.1% CH4, 11% CO2, 17% H2, 22% CO, and 47% N2. The results show that the coprecipitated Zn-promoted catalyst had higher extent of reduction and carburization, which led to higher carbon conversion and C5+ selectivity of this CO2-rich syngas than the impregnated catalyst.

Combined molten salt–Ni/Al2O3 as synergistic medium for high-quality syngas production

Proposed synergistic use of a combined medium of molten salt and Ni/Al2O3 (MS-Ni) was investigated for its enhancement of cellulose pyrolysis for high-quality syngas production. Clean renewable solar energy is to be stored at a high temperature in molten salt (MS) and provides the heat of pyrolysis. The MS-Ni medium could increase H2 yield by 3-folds while CO yield slightly increased by 15%, compared to the case of only MS medium. The peak rate of H2 production nearly quadrupled while the peak rate of CO production increased 2.5times at about 150 and 80K lower temperatures, respectively. The ratio of selectivity of syngas to undesired CH4 was nearly doubled. Arrhenius rate expressions for pseudo-first-order pyrolytic reaction are derived from the experimental data to give activation energies of 206 and 128kJmol−1 for the MS and the MS-Ni mediums, respectively. The experimental results clearly validated the role of MS-Ni as a synergistic medium for high-quality syngas production from cellulosic biomass pyrolysis.

Tunable ceria–zirconia support for nickel–cobalt catalyst in the enhancement of methane dry reforming with carbon dioxide

Ceria–zirconia mixed oxides (CeZr) were glycol-thermally synthesised as nano-crystalline supports with tunable ratios for the anchoring of nickel–cobalt (Ni–Co) catalyst to enhance methane dry reforming (MDR) reaction with carbon dioxide. High conversion of methane (90%) and carbon dioxide (92%), good output (H2=32%; CO=44%), and selectivity and stability of syngas prove the effectiveness of the catalyst deposited on this support. 80:20 for Ce:Zr was identified as the optimal ratio to attain active and stable catalytic performance in MDR, with a low coking content of 0.47wt.%.

Chemical-Looping Steam Methane Reforming over a CeO2–Fe2O3 Oxygen Carrier: Evolution of Its Structure and Reducibility

Chemical-looping steam methane reforming (CL-SMR) is a promising method for the co-generation of pure hydrogen and syngas on the basis of redox cycles via a gas–solid reaction using an oxygen carrier. The performance and life of the oxygen carrier play pivotal roles in determining the feasibility and economy of the CL-SMR process. The present research was focused on the evolution of the structure and reducibility of a CeO2–Fe2O3 oxygen carrier during the CL-SMR redox process to further understand the sustainability of the oxygen carrier. The investigated CeO2–Fe2O3 complex oxide exhibited satisfactory performance in the CL-SMR process because of the chemical interaction between Ce and Fe species. A Ce–Fe–O phase equilibrium based on a stable composition of CeO2, Fe3O4, and CeFeO3 formed in the recycled samples. Surface oxygen was removed, which was accompanied by an increase in the concentration of oxygen vacancies and a decrease in the surface area of the recycled samples; these effects resulted in an increase in the high-temperature reducibility and syngas selectivity of the samples. Oxygen mobility was intensified by the Ce–Fe chemical interaction via the formation of CeFeO3 and a micromorphological transformation. These properties counteracted the sintering of the materials and guaranteed the stability of the oxygen carrier in the CL-SMR process.

Barium Substituted Lanthanum Manganite Perovskite for CO2 Reforming of Methane

Barium substituted lanthanum manganite La1–xBaxMnO3 (x = 0.10–0.50) of a single phase perovskite structure was used as catalysts for CO2 reforming of CH4 for the first time. The optimal level of Ba substitution (Ba/Mn = 0.10, 0.15) produced La1–xBaxMnO3 of high surface area, uniform particle dispersion, and highly ordered pores. The optimally substituted perovskite catalysts showed much improved reducibility of Mn3+/Mn4+ to Mn2+ to provide oxygen vacancies and rapid migration of lattice oxygen from the bulk toward the surface. The ability of donating lattice oxygen to the catalytic cycle seems responsible for the facilitated decomposition and dissociation of CH4 and CO2, which led to high conversions, excellent syngas selectivity, and stability with little coke formation. The addition of oxygen to the dry reforming reaction showed improved conversion and selectivity to syngas by making catalysts less prone to coke formation. To the best of our knowledge, the results represent the first example of Mn-based...

CO2 reduction to syngas and carbon nanofibres by plasma-assisted in situ decomposition of water

Simultaneous activation of CO2 and H2O was carried out in a non thermal plasma dielectric barrier discharge reactor operated under ambient conditions. The plasma reactor packed with partially reduced NiO/Al2O3 catalyst showed better CO2 conversion than both the unreduced NiO/Al2O3 and with plasma (no catalyst), whereas, highest syngas selectivity was observed with unreduced NiO/Al2O3. An interesting observation is the formation of carbon nanofibres (CNFs) along with syngas with a reduced NiO catalyst integrated to the plasma, whereas, pure NiO only led to the formation of methane. The reduction of CO2 by in situ formation of hydrogen from water splitting may produce CH4 and plasma-assisted chemical vapour decomposition of CH4 may lead to the formation of CNFs.

Catalytic Nonthermal Plasma Reactor for Dry Reforming of Methane

Co-processing of two greenhouse gases, methane and carbon dioxide, was carried out in a dielectric barrier plasma reactor. The influence of feed gas proportion on the performance of the plasma reactor was investigated, especially with an objective to increase the conversion of the reactants and selectivity to syngas. To understand the influence of the catalyst on dry reforming, 10–30% NiO/Al2O3 catalysts were prepared by a single-step combustion synthesis and various physicochemical techniques confirmed the formation of nanosized Ni particles. A total of 10% of the discharge volume was packed with Ni/Al2O3 catalysts in a packed-bed configuration. An interesting observation is the increased syngas selectivity on the addition of catalyst to plasma, and among the catalysts tested, 20% Ni showed a H2/CO ratio of 2.25 against 1.2 with a plasma reactor alone.

Operation of a solid oxide fuel cell on a reformed FAME mixture

The operation of a solid oxide fuel cell (SOFC) using a reformed fatty acid methyl ester (FAME) mixture a biodiesel-like fuel, has been successfully demonstrated. This project had two main aspects: 1) determining the fuel reforming activity of a pyrochlore catalyst deposited onto a monolith; and 2) operating a SOFC on reformed fuel gas. Prior to integrated testing, parametric reforming studies of the FAME mixture were conducted using both Rh/γ-Al2O3 and Rh-substituted pyrochlore catalyst powders to determine the operating conditions to maximize syngas selectivity. Using the same pyrochlore catalyst as in the parametric studies, a monolith reformer converted 0.5 cm3 min−1 of the FAME mixture into mostly hydrogen and carbon monoxide (syngas). The syngas generated in the reformer was sent to an anode supported SOFC (H.C. Starck Ceramics GmbH & Co.) The SOFC operated on 98% H2/2% H2O for baseline testing before and after switching to the reformed FAME mixture for 100 h of operation. The results presented here demonstrate that FAME mixture can be successfully reformed to power a SOFC, making them a viable fuel for a SOFC-based auxiliary power unit that is both greenhouse gas neutral and renewable.

The assessment of reformation in a porous medium-catalyst hybrid reformer under excess enthalpy condition

A porous medium-catalyst hybrid reformer for hydrogen-rich syngas production by dry autothermal reforming (DATR) was investigated in this study. In the reforming process, the reaction under excess enthalpy was explored by visualization in packed-bed catalyst reactor. The hybrid design was arranged with a porous medium (PM) in the upstream of the catalyst packed-bed. In the arrangement, the reactants were preheated by internal heat recirculation and the selectivity of H2-rich syngas was enhanced by the catalyst surface reaction. Controlled parameters included CO2/CH4 and O2/CH4 ratios, gas hourly space velocity (GHSV) with or without porous medium. The experimental results demonstrated that the reforming reaction with the hybrid reformer could achieve excess enthalpy under the tested parameters. The excess enthalpy ratio was between 0.15 and 0.55. The temperature measurement along the axial position and image observation of the catalyst packed-bed indicated that the flame was stably held at the interface of the PM and the catalyst bed, and this enhanced fuel conversion and reforming efficiencies, especially in the low methane conversion condition. In the dry autothermal reforming process, part of the chemical energy released from the reaction supplies the energy required for a self-sustaining reaction. Therefore, the selection of the parameters was determined to achieve high reforming efficiency and low energy loss percentage. The results showed that the energy loss percentage was between 12.7 and 24.6% and reforming efficiency was between 64.4 and 79.5% with the best reforming parameter settings (O2/CH4 = 0.7–0.9 and CO2/CH4 = 0.0–2.0).

Dry autothermal reforming from biomass derived gas under excess enthalpy with porous medium

Dry autothermal reforming (DATR) from biomass derived gas (BDG) under excess enthalpy with porous medium (PM) is investigated in this study. Preheating reactant by internal heat recirculation of a PM may enhance the reaction of input mixture and improve production of H2-rich syngas. Temperature distribution of catalyst and fuel conversion efficiency are studied with various feeding rates of reactant and PM under high-temperature and carbon-rich conditions. Fuel conversion and H2-rich syngas selectivity are improved by reactant preheating with increased enthalpy of reactant by the heat transfer stored in PM. Control parameters include methane feeding rate, CO2/CH4 and O2/CH4 molar ratios, and PM material. Experimental results indicate that reformate gas temperature with PM-assisted dry autothermal reforming is higher than the equilibrium adiabatic temperature. The results are helpful to understand the internal heat recirculation under excess enthalpy reaction. In the reforming, it not only provides the required energy for a self-sustaining reaction, but also enhances fuel conversion efficiency. The improvements in methane conversion efficiency is 18%, energy loss percentage 20.7%, and reforming efficiency 33.9%, respectively with the best parameter settings by an OBSiC PM. Additionally, the theoretical production is calculated by the HSC Chemistry software (ChemSW Software, Inc.).

Improving selectivity by the addition of N2O in the feed during partial oxidation of methane over supported rhodium catalysts

New results studying the effects brought about by the introduction of small amounts of N2O in the gas feed (promoter) during the partial oxidation of methane (POM) over Rh/γ-Al2O3 and Rh/MgO catalysts are presented. Standard tests were performed with 5vol.% CH4, 2.5vol.% O2, and balanced with N2. When small amounts of N2O (300ppm, 1000ppm) were added to the feed, yield and selectivity to H2 and CO increased. Under these conditions rhodium works in a reduced state, resulting in the enhancement of syngas selectivity and the inhibition of the total oxidation of methane. This effect tends to disappear after a certain period of time when N2O supply is cut. The effect is reversible. It is suggested that N2O is adsorbed on the vacancies where O2 does, inhibiting the formation of oxidant (electrophilic) oxygen species produced by dissociation of O2 on the same vacancies. In the presence of N2O, rhodium remains in a reduced oxidation state. Reduced rhodium modifies the kinetics of all reactions involved under POM reaction conditions and promotes synthesis gas.