Improvements in hydrogen production from methane dry reforming on filament-shaped mesoporous alumina-supported cobalt nanocatalyst

The mesoporous gamma-alumina (γ-Al₂O₃) synthesized via evaporation-induced self-assembly method (EISA) using inorganic salt, Al(NO₃)₃·9H₂O precursor and water-ethanol solvent mixture was implemented as a support for Co catalyst in methane dry reforming at 973–1073 K under 1 atm. The γ-Al₂O₃ support possessed filament-shaped morphology with surface area of 173.4 m² g^?1 and cobalt nanoparticles were successfully dispersed on support with small crystallite size of 7.8 nm. The stability of 10%Co/Al₂O₃ was evident for CH₄ and CO₂ conversions at 1023 and 1073 K. CH₄ conversion could reach to 76.2% while 81.6% was observed for CO₂ conversion at 1073 K. Although graphitic and amorphous carbons were unavoidably formed on used catalyst, 10%Co/Al₂O₃ exhibited an outstanding performance comparable to noble metals with the desired ratio of H₂/CO for downstream Fischer-Tropsch process.     

Carbon dioxide reforming of methane to syngas over ordered mesoporous Ni/KIT-6 catalysts

The ordered mesoporous Ni/KIT-6 (KIT-6, an ordered mesoporous SiO₂) catalysts were prepared by impregnation method for carbon dioxide reforming of methane. The physicochemical properties of the prepared catalysts were characterized by H₂-TPR, XRD, BET, and TEM. The research results show that the specific surface area, pore diameter, crystal size of Ni species, and catalytic performance of the Ni/KIT-6 catalysts are obviously affected by the Ni content. Increasing Ni content results in the increment of the crystal size of Ni species, while the dispersion of Ni species shows the opposite trend. The specific surface area and pore size of the Ni/KIT-6 catalyst with the Ni loading of 3 wt% were 493.3 m² g^?1 and 6.22 nm, respectively. Besides, the Ni species are highly dispersed on the surface of KIT-6 support. Thereby, it exhibits the superior catalytic performance of carbon dioxide reforming of methane to syngas (CO and H₂). At atmospheric pressure, the CO₂ and CH₄ conversions for each catalyst following the order: NK3 ≈ NK4 > NK5 > NK2 > NK1 > bulk Ni. When the reaction temperature is 600 °C, the conversions of CH₄ and CO₂ of the NK3 catalyst are 65.1% and 37.0%, respectively. Meanwhile, it also shows excellent stability.     

Kinetic and autocatalytic effects during the hydrogen production by methane decomposition over carbonaceous catalysts

The reaction kinetics of methane decomposition to yield hydrogen and carbon has been investigated comparing different types of carbonaceous catalysts: two ordered mesoporous carbons (CMK-3 and CMK-5) and two commercial carbon blacks (CB-bp and CB-v). The evolution of the reaction rate along the time has been analyzed concluding that it is governed by different and opposite events: reduction of active sites by carbon deposition, autocatalytic effects of the carbon deposits and pore blockage and diffusional constraints. A relatively simple kinetic model has been developed that fits quite well the experimental reaction rate curves in spite of the complexity of the involved phenomena.     

Ordered mesoporous alumina supported nickel based catalysts for carbon dioxide reforming of methane

Ordered mesoporous alumina facilely synthesized via improved evaporation-induced self-assembly (EISA) strategy was provided with large specific surface area, big pore volume, uniform pore size and excellent thermal stability. The obtained mesoporous material was used as the carrier of the Ni based catalysts for carbon dioxide reforming of methane. These mesoporous catalysts performed high catalytic activity and long stability. Typically, the catalytic conversions of the CH₄ and CO₂ were greatly close to the equilibrium conversion and no deactivation was observed during the 100 h long lifetime test. The advantageous structural properties of ordered mesoporous alumina contributed to high dispersion of the Ni particles among the mesoporous framework, which further accounted for the good catalytic activity due to more “accessible” Ni active sites for the reactants. The “confinement effect” of the mesopores could effectively prevent the thermal sintering of the Ni nanoparticles to some extent, committed to its long-term catalytic stability. Besides, the mesoporous catalysts possessed enhanced ability to withstand coke, although not any modifiers had been added. Properties of the coke over the mesoporous catalyst were also carefully investigated. Therefore, the ordered mesoporous alumina was a promising catalyst support for the carbon dioxide reforming with methane.     

La-doped cobalt supported on mesoporous alumina catalysts for improved methane dry reforming and coke mitigation

The promotional La₂O₃ effect on the physicochemical features of mesoporous alumina (MA) supported cobalt catalyst and its catalytic performance for methane dry reforming (MDR) was examined at varied temperature and stoichiometry feedstock. The Co₃O₄ nanoparticles were evidently scattered on fibrous mesoporous alumina with small crystal size of 8–10 nm. The promotion behavior of La₂O₃ facilitated H₂-reduction by providing higher electron density and enhanced oxygen vacancy in 10%Co/MA. The addition of La₂O₃ could reduce the apparent activation energy of CH₄ consumption; hence, increasing CH₄ conversion up to 93.7% at 1073 K. The enhancement of catalytic activity with La₂O₃ addition was also due to smaller crystallite size, alleviated H₂-reduction and the basic character of La₂O₃. Lanthanum dioxycarbonate transitional phase formed in situ during MDR was accountable for mitigating deposited carbon via redox cycle for 17–30% relying on reaction temperature. Additionally, the oxygen vacancy degree increased to 73.3% with La₂O₃ promotion. The variation of H₂/CO ratios within 0.63–0.99 was preferred for downstream generation of long-chain olefinic hydrocarbons.     

Effect of ruthenium addition on molybdenum catalysts for syngas production via catalytic partial oxidation of methane in a monolithic reactor

Hydrogen is mainly produced from hydrocarbon resources. Natural gas, mostly composed of methane, is widely used for hydrogen production. As a valuable feedstock for ‘Fischer–Tropsch’ (FT) process and ‘Gas to Liquids’ (GTL) technology, syngas production from catalytic partial oxidation of methane (CPOM) is gaining prominence especially owing to its more desirable H₂/CO ratio; relatively less energy consumption, and lower investment, compared to steam reforming processes (SMR), the leading technology.In the present study, effect of ruthenium (Ru) addition on molybdenum (Mo) catalysts for syngas production from methane (CH₄) via partial oxidation in a monolithic reactor was investigated. Mo based catalysts supported on Nickel (Ni) and Cobalt (Co) metal oxides and Ni-Co bimetallic oxides and their Ru added versions were developed, characterized, and tested for performance in a monolithic type reactor system. Catalyst activity was investigated in terms of H₂ and CO selectivity, CH₄ conversion; and CO₂ emission and it is concluded that addition of Ru over the structure led to increase in catalytic activity and reduction in carbon deposition over the catalyst surface.     

Yttrium-stabilized zirconia-promoted metallic nickel catalysts for the partial oxidation of methane to hydrogen

A metallic Ni catalyst has been prepared with nickel sponge and further promoted with YSZ (yttrium-stabilized zirconia) by an impregnation method. The catalysts are characterized by ICP, BET, SEM, XRD and H₂-TPR, and then studied for the partial oxidation of methane to hydrogen. The influences of reaction temperature, CH₄/O₂ ratios and gas hourly space velocity on the reaction rate are investigated. The catalyst characterization results show that the YSZ-promoted metallic Ni catalysts have high specific surface area; there is more NiO phase in the YSZ-promoted catalysts than in the metallic Ni catalyst; a mutual diffusion of Ni²⁺ and Zr⁴⁺ ions might happen between the NiO and YSZ phases. The reaction results show that the YSZ promotion increases the CH₄ conversion and the selectivities to H₂ and CO.     

Partial oxidation of methane over CeO2 loaded hydrotalcite (MgNiAl) catalyst for the production of hydrogen rich syngas (H2, CO)

In this work, partial oxidation of methane (POM) was investigated using Mg-Ni-Al (MNA) hydrotalcite promoted CeO₂ catalyst in a fixed bed reactor. MNA hydrotalcite was synthesized using the co-precipitation process, while CeO₂ was incorporated via the wetness impregnation technique. The CeO₂@MNA samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) technique. The catalytic activity of CeO₂ promoted MNA (CeO₂@MNA) for POM reaction was evaluated for various CeO₂ loading kept the feed ratio CH₄/O₂ = 2 at 850 °C. The catalyst containing 10 wt% cerium loading (10%CeO₂@MNA) showed 94% CH₄ conversion with H₂/CO ratio above 2.0, that is more suitable for FT synthesis. The performance of catalyst is attributed to highly crystalline stable CeO₂@MNA with better Ce-MNA interactions withstand for 35 h time on stream. Furthermore, the spent catalyst was examined by TGA, SEM-EDS, and XRD to evaluate the carbon formation and structural changes during the span of reaction time.     

Experimental and numerical study of detailed reaction mechanism optimization for syngas (H2 + CO) production by non-catalytic partial oxidation of methane in a flow reactor

The National Institute of Standards and Technology (NIST) detailed reaction mechanism of methane combustion was optimized based on a flow reactor experiment to obtain syngas (H₂ + CO). The experimental methane partial oxidation was conducted with pre-mixed gas in a flow reactor. Specifically, 0.2% methane and 0.1% oxygen were diluted with 99.7% argon, restraining the exothermic effect. The experiment was conducted from 1223 K to 1523 K under pressure. Through a comparison of the experimental results with calculated values, the NIST mechanism was selected as a starting point. Rate coefficients of O + OH = O₂ + H, CH₃ + O₂ = CH₃O + O, and C₂H₂ + O₂ = HCCO + OH were replaced with results from other studies. The replaced rate coefficient for CH₃ + O₂ = CH₃O + O was again optimized, within its reported uncertainty of 3.16, based on the experimental results of this study. The revised value of the rate coefficient for CH₃ + O₂ = CH₃O + O was k₃₇ = 7.92 × 10¹³ × e^{(−31400/RT)}. The optimized mechanism showed better performance in predicting the results of other studies, as well as this study. The optimization reduced the RMS error for the results of this study from 6.7 to 1.18.     

Partial oxidation of methane on neodymium and lanthanium chromate based perovskites for hydrogen production

Perovskite-type mixed oxides LaCrO₃ and Nd_0.95CrO₃ were synthesized by the polymerization complex method. The perovskites were characterized by different techniques aiming to evaluate the influence of the non-stoichiometry and the nature of site A on the catalytic properties for the POM reaction. The non-stoichiometry and A sites did not affect the methane conversion, but the selectivity. The methane conversion with the neodymium catalyst Nd_0.95CrO₃ (N95) was 34%, and of the mixed La_0.95CrO₃ (L95) catalyst 38%, under these conditions. The rate of the Nd_0.95CrO₃ (N95) perovskite was equal to 3.50 mol.g⁻¹.h⁻¹ at 700 °C, which suggests higher activity compared to cobaltate perovskites. Although the hydrogen selectivity was similar the selectivity to CO and CO₂ were different. Catalysts did not suffer structure changes during the POM reaction and negligible deactivation.     

Zirconia-supported tungsten oxides for cyclic production of syngas and hydrogen by methane reforming and water splitting

ZrO₂-supported tungsten oxides were used for cyclic production of syngas and hydrogen by methane reforming (reduction) and water splitting (re-oxidation). The reduction characteristics of WO₃ to WO₂ and WO₂ to W were examined at various temperatures (1073–1273 K) and reaction times. Significant portions of the tungsten oxides were also reduced by the produced H₂ and CO. The extent of reduction by H₂ varied greatly depending on temperature and WO₃ content and also on the reduction of either WO₃ or WO₂, while that by CO was consistently low. When the overall degree of reduction became sufficiently high, methane decomposition started to proceed rapidly, resulting in considerable carbon deposition and H₂ production. Consequently, the H₂/(CO + CO₂) ratio varied from around 1 to higher than 2. During the repeated cyclic operations with a proper reduction time at a given temperature, the syngas and hydrogen yields decreased gradually while the H₂/(CO + CO₂) ratio remained nearly constant and the carbon deposition was negligible.     

High temperature iron-based catalysts for hydrogen and nanostructured carbon production by methane decomposition

The production of hydrogen and filamentous carbon by means of methane decomposition was investigated in a fixed-bed reactor using iron-based catalysts. The effect of the textural promoter and the addition of Mo as a dopant affects the catalysts performance substantially: iron catalyst prepared with Al₂O₃ showed slightly higher catalytic performance as compared to those prepared with MgO; Mo addition was found to improve the catalytic performance of the catalyst prepared with MgO, whereas in the catalyst prepared with Al₂O₃ displayed similar or slightly poorer results. Additionally, the influence of the catalyst reduction temperature, the reaction temperature and the space velocity on the hydrogen yield was thoroughly investigated. The study reveals that iron catalysts allow achieving high methane conversions at operating temperatures higher than 800 °C, yielding simultaneously carbon nanofilaments with interesting properties. Thus, at 900 °C reaction temperature and 1 l g⁻¹_cat h⁻¹ space velocity, ca. 93 vol% hydrogen concentration was obtained, which corresponds to a methane conversion of 87%. Additionally, it was found that at temperatures higher than 700 °C, carbon co-product is deposited mainly as multi walled carbon nanotubes. The textural and structural properties of the carbonaceous structures obtained are also presented.     

Hydrogen and/or syngas production by combined steam and dry reforming of methane on nickel catalysts

Two alumina supported Ni catalysts with pore sizes of 5.4 nm and 9 nm were synthetized, characterized and tested in the Combined Steam and Dry Reforming of Methane (CSDRM) for the production of hydrogen rich gases or syngas. The reaction mixture was designed to simulate the composition of real clean biogas, the addition of water being made in order to have molar ratios of H₂O:CO₂ corresponding to 2.5:1, 7.5:1 and 12.5:1. Structural and functional characterization of catalysts revealed that Ni/Al₂O₃ with larger pore size shows better characteristics: higher surface area, lower Ni crystallite sizes, higher proportion of stronger catalytic sites for hydrogen adsorption, and higher capacity to adsorb CO₂. At all studied temperatures, for a CH₄:CO₂:H₂O molar ratio of 1:0.48:1.2, a (H₂+CO) mixture with H₂:CO ratio around 2.5 is obtained. For the production of hydrogen rich gases, the optimum conditions are: CH₄:CO₂:H₂O = 1:0.48:6.1 and 600 °C. No catalyst deactivation was observed after 24 h time on stream for both studied catalysts, and no carbon deposition was revealed on the used catalysts surface regardless the reaction conditions.     

Syngas production by integrating CO2 partial gasification of pine sawdust and methane pyrolysis over the gasification residue

The aim of this work was to study syngas production by integrating CO₂ partial gasification (for CO production) of pine sawdust (PS) and methane pyrolysis (for H₂ production) over the gasification residue. Effect of the gasification conditions (including CO₂ flow rate, reaction temperature, mass ratio of PS:Ni and reaction time) was investigated on properties of the gasification residue. Besides CO-rich gas released from the gasification process with CO₂ conversion up to about 92%, the gasification residue could serve as robust catalyst for H₂ production by methane pyrolysis. Thanks to the nickel crystallites formed with high reduction degree and high dispersion on the surface after the gasification process, the gasification residue was competent for high and stable methane conversion (about 91%) at 850 °C. In addition to the flexible syngas output (in theory, with an arbitrary ratio of H₂/CO), valuable filamentous carbons can be achieved by regulating the process parameters.     

Life cycle assessment of hydrogen production by methane decomposition using carbonaceous catalysts

Methane decomposition to yield hydrogen and carbon (CH₄ ? 2H₂ + C) is one of the cleanest alternatives, free of CO₂ emissions, for producing hydrogen from fossil fuels. This reaction can be catalyzed by metals, although they suffer a fast deactivation process, or by carbonaceous materials, which present the advantage of producing the catalyst from the carbon obtained in the reaction. In this work, the environmental performance of methane decomposition catalyzed by carbonaceous catalysts has been evaluated through Life Cycle Assessment tools, comparing it to other decomposition processes and steam methane reforming coupled to carbon capture systems. The results obtained showed that the decomposition using the autogenerated carbonaceous as catalyst is the best option when reaction conversions higher than 65% are attained. These were confirmed by 2015 and 2030 forecastings. Moreover, its environmental performance is highly increased when the produced carbon is used in other commercial applications. Thus, for a methane conversion of 70%, the application of 50% of the produced carbon would lead to a virtually zero-emissions process.     

Stepwise production of syngas and hydrogen through methane reforming and water splitting by using a cerium oxide redox system

Stepwise production of syngas and hydrogen from ZrO₂-supported CeO₂ through methane reforming and water splitting was investigated in order to find proper operating conditions under which carbon deposition could be minimized. Recommendable operating temperature and time were 1073 K and 30 min for both the methane reforming and the water splitting. Even though the H₂/CO ratio during the methane reforming was maintained close to the desired ratio of 2, undesirable methane cracking occurred to a small extent and further reduction of Ce₂O₃ to metallic Ce by CH₄ and H₂ occurred to some extent. When the methane reforming-water splitting cyclic operations were repeated, the yields of syngas and hydrogen decreased considerably from the first cycle to the second cycle, but from the second cycle to the fifth cycle the gas yields were maintained nearly constant. As the CeO₂ content in the sample increased, the gas yields per mole of CeO₂ decreased but the gas productions per gram of sample increased.     

Support effects on the properties of Co and Ni catalysts for the hydrogen production from bio-ethanol partial oxidation

Partial oxidation of bio-ethanol over Co- and Ni-based catalysts supported on Al₂O₃, ZnO and AlZn binary mixed oxide was studied in a temperature range between 300 and 600 °C. Substantial difference in catalytic behavior of the materials was related to variation in metal dispersion and to metal-support interaction realized on different supports. Hence, the state of active metallic phase and reducibility of the catalysts were investigated. Among the presented systems, Ni supported on AlZn mixed oxide prepared by sol–gel method afforded the most active catalyst producing a H₂ and CO rich fuel gas. It is proposed that ZnAl₂O₄ spinel phase determines the reaction pathway and Ni promote the hydrogen generation. High hydrogen selectivity of around 90% at complete ethanol conversion was achieved at 600 °C, whereas CO, CO₂ and insignificant amounts of CH₄ were the only carbon-containing products. This high catalytic performance combined with the low cost metals and the supports used in this study makes the materials prepared herein attractive as candidates for hydrogen generation by catalytic partial oxidation of bio-ethanol.     

Modeling study on the production of hydrogen/syngas via partial oxidation using a homogeneous charge compression ignition engine fueled with natural gas

The production of hydrogen and syngas from natural gas using a homogeneous charge compression ignition reforming engine is investigated numerically. The simulation tool used was CHEMKIN 3.7, using the GRI-3 natural gas combustion mechanism. This simulation was conducted on the changes in hydrogen and syngas concentration according to the variations of equivalence ratio, intake temperature, oxygen enrichment, engine speed, initial pressure, and fuel additives with partial oxidation combustion. The simulation results indicate that the hydrogen/syngas yields are strongly dependent on the equivalence ratio with maxima occurring at an optimal equivalence ratio varying with engine speed. The hydrogen/syngas yields increase with increasing intake temperature and oxygen contents in air. The hydrogen/syngas yields also increase with increasing initial pressure, especially at lower temperatures, yet high temperature can suppress the pressure effect. Furthermore, it was found that the hydrogen/syngas yields increase when using fuel additives, especially hydrogen peroxide. Through the parametric screening studies, optimum operating conditions for natural gas partial oxidation reforming are recommended at 3.0 equivalence ratio, 530 K intake temperature, 0.3 oxygen enrichment, 500 rpm engine speed, 1 atm initial pressure, and 7.5% hydrogen peroxide.     

Catalytic performance and characterization of Neodymium-containing mesoporous silica supported nickel catalysts for methane reforming to syngas

Ordered mesoporous silica materials based on nickel and other elements have been extensively studied because controlling the size of metal nanoparticles is an effective method to tune the superficial physicochemical process. Neodymium (Nd)-promoted mesoporous silica xNdMS (x: molar ratio of Nd/Si = 0.01, 0.02, 0.04, 0.06) were prepared through a sol–gel strategy. Nickel-based catalysts with high dispersion by using xNdMS as supports were investigated for methane reforming with carbon dioxide and/or oxygen to produce syngas. xNdMS supports and nickel catalysts were examined by combining textural, structural, local and surface information. The characterization results showed that Nd was successfully incorporated into the mesoporous framework of MS and Nd was beneficial to improve the metal dispersion. All Nd-promoted Ni/MS catalysts were effective for the methane reforming reaction. Ni/0.04NdMS catalyst exhibited the highest initial catalytic activity during 12 h time on stream, which was attributed to its high metal dispersion, more basic sites and the strengthened nickel-support interaction. The readily deactivation and poorest catalytic activity of Ni/MS catalyst were due to the serious oxidation of metallic nickel under reaction medium.     

Combined dry reforming and partial oxidation of methane to synthesis gas on noble metal catalysts

In this paper CO₂ reforming of methane combined with partial oxidation of methane to syngas over noble metal catalysts (Rh, Ru, Pt, Pd, Ir) supported on alumina-stabilized magnesia has been studied. The catalysts were characterized by using BET, XRD, SEM, TEM, TPR, TPH and H₂S chemisorption techniques. The H₂S chemisorption analysis showed an active metal crystallite size in the range of 1.8-4.24 nm for the prepared catalysts. The obtained results revealed that the Rh and Ru catalysts showed the highest activity in combined reforming and both the dry reforming and partial oxidation of methane. The obtained results also showed a high catalytic stability without any decrease in methane conversion up to 50 h of reaction. In addition, the H₂/CO ratio was around 2 and 0.7 over different catalysts for catalytic partial oxidation and dry reforming, respectively.