Influence of the operating parameters over dry reforming of methane to syngas

The influence of operating parameters over dry reforming of methane reaction was evaluated using a Ni-based catalyst obtained after calcination of a hydrotalcite-like precursor. The studied variables were mass to flow ratio (W/F), reaction temperature and CO₂/CH₄ ratio. Maximum methane and carbon dioxide conversions were achieved at W/F ratios above 0.21 g h L⁻¹. The higher the W/F ratio was, the lower amount of water was formed, which led to a higher H₂/CO ratio. The increase in reaction temperature produced an increase in conversions. Water concentration in the outlet stream showed a maximum at 600 °C. At this temperature, reverse water–gas-shift reaction (RWGS) was favoured because it is endothermic. However, steam reforming and carbon gasification were also favoured and they consumed great part of the water produced. CO₂/CH₄ ratios above 1 led to a higher CH₄ conversion but selectivity to hydrogen decreased because RWGS reaction was favoured. When CO₂/CH₄ was below unity, CH₄ conversion decreased but less amount of water was produced so a higher H₂ selectivity was achieved. The catalyst exhibited good stability over dry reforming of methane under all the tested conditions, which may be ascribed to its high basicity. This property improved CO₂ adsorption and then RWGS reaction and carbon gasification.     

Fe/HZSM-5 synergizes with biomass pyrolysis carbon to reform CH4–CO2 to syngas in microwave field

CO₂ reforming of CH₄ to syngas, an important chemical raw material, has received widespread attention. However, the use of noble metal catalysts and high energy consumption limit their application. In this study, microwave-assisted dry reforming over mixtures of Fe/HZSM-5 and biomass pyrolysis carbon (BPC) was studied. Additionally, the influence of different reaction conditions and catalysts on the reforming efficiency was examined. Our results demonstrated that microwave heating improved the dry reforming process while reducing the cost of catalysts used. At a microwave power of 700 W, and the space velocity of 2.4 L/(h?g), CO₂ and CH₄ conversion reached 91.27% and 63.03%, respectively. In addition, Fe/HZSM-5 showed synergistic effects with BPC, and the migration of active metals was responsible for the synergistic effects. The microwave reforming effect was better than that of conventional heating reforming, and the unique effects of microwave fields facilitated the conversion process. This study makes a useful contribution to the improvement of new dry reforming methods.     

Efficient recovery of syngas from dry methane reforming product by a dual pressure swing adsorption process

In recent years, there has been growing interest in the dry reforming of methane (using CO₂ instead of H₂O) to obtain syngas, due to its economic and environmental advantages. In this reaction, to achieve conversions close to 100%, it is necessary to work at temperatures higher than 1000 °C. However, to attenuate the catalyst deactivation by sintering is convenient to work at lower temperatures, so that normally the syngas (mixture CO + H₂) is obtained mixed with unreacted CO₂ and CH₄. In this work a process has been simulated to recover the syngas from the product of a dry reforming reaction of methane at 700 °C by means of a Dual PSA (Dual Pressure Swing Adsorption) process with heavy reflux using BPL activated carbon as an adsorbent, operating at 25 °C. The process can recover syngas with purity and recovery higher than 99%. Unreacted CO₂ and CH₄ can be recycled to the reactor, leading to effective CO₂ and CH₄ conversions close to 100%. The process specific energy input (SEI) is 4.7 thermal kJ per L (STP) of syngas. The process can also be used to recover the syngas contained in the tail gas of a H₂ purification PSA from SMR-off gas.     

Hydrogen production from biogas reforming and the effect of H2S on CH4 conversion

Biogas produced during anaerobic decomposition of plant and animal wastes consists of high concentrations of methane (CH₄), carbon dioxide (CO₂) and traces of hydrogen sulfide (H₂S). The primary focus of this research was on investigating the effect of a major impurity (i.e., H₂S) on a commercial methane reforming catalyst during hydrogen production. The effect of temperature on CH₄ and CO₂ conversions was studied at three temperatures (650, 750 and 850 °C) during catalytic biogas reforming. The experimental CH₄ and CO₂ conversions thus obtained were found to follow a trend similar to the simulated conversions predicted using ASPEN plus. The gas compositions at thermodynamic equilibrium were estimated as a function of temperature to understand the intermediate reactions taking place during biogas dry reforming. The exit gas concentrations as a function of temperature during catalytic reforming also followed a trend similar to that predicted by the model. Finally, catalytic reforming experiments were carried out using three different H₂S concentrations (0.5, 1.0 and 1.5 mol%). The study found that even with the introduction of small amount of H₂S (0.5 mol%), the CH₄ and CO₂ conversions dropped to about 20% each as compared to 65% and 85%, respectively in the absence of H₂S.     

Effect of H2S on carbon-catalyzed methane decomposition and CO2 reforming reactions

The effect of H₂S on catalytic processing of methane is of a great practical importance. In this work, the effect of small quantities (0.5–1.0 vol.%) of H₂S present in the feedstock on the methane decomposition and CO₂ reforming reactions over carbon and metal based catalysts was investigated. Activated carbon (FY5), an in-house prepared alumina-supported Ni catalyst (NiA) and the mixture of both (FY5 + NiA) were used as catalysts in this study. It was found that CH₄ and CO₂ conversions were noticeably increased when H₂S was added to the reacting mixture, which points to (i) the tolerance of carbon catalyst to H₂S and (ii) the catalytic effect of H₂S on carbon-catalyzed decomposition and dry reforming of methane. In contrast, NiA catalyst and the mixture FY5 + NiA were deactivated in the presence of H₂S in both reactions. The effect of the heating system (i.e., conventional electric resistance vs microwave heating) on the products yield of the dry reforming reaction in the presence of H₂S is also discussed in this paper.     

Study on hydrogen-rich syngas production by dry autothermal reforming from biomass derived gas

In this study, the H₂-rich syngas (H₂ + CO) production from biomass derived gas (BDG) by dry autothermal reforming (DATR) is investigated. Methane and carbon dioxide is the major composition of biomass derived gas. DATR reaction combined benefits of partial oxidation (POX) and dry reforming (DR) reaction was carried out in this study. The reforming parameters on the conversion of methane and syngas selectivity were explored. The reforming parameters included the fuel feeding rate, CO₂/CH₄ and O₂/CH₄ molar ratios. The experimental results demonstrated that it not only supplied the energy required for self-sustained reaction, but also avoided the coke formation by dry autothermal reforming. It has a wide operation region to maintain the moderate production of the syngas. During the reforming process, the reformate gas temperature was between 650 and 900 °C, and energy loss percentage in reforming process was between 15 and 30%. Further, high CO₂ concentration in the reactant had a considerable influence on the heat release of oxidation, and thereby decreased the reformate gas temperature. It caused the reduction of synthesis gas concentration and assisting/impeding combustion composition (A/I) ratio. However, it was favorable to CO selectivity because of the reverse water-gas shifting reaction. The H₂/CO molar ratio between 1 and 2 was achieved by varying CO₂/CH₄ molar ratio. However, the syngas concentrations were affected by CO₂/CH₄ and O₂/CH₄ molar ratio.     

Factors influencing CH4CO2 reforming reaction over Fe catalyst supported on foam ceramics under microwave irradiation

In this work, a CH₄CO₂ reforming reaction was carried out under microwave irradiation using Fe/(SiC·SiO₂) and Fe/(Al₂O₃·SiC) catalysts. The temperature-change behavior of the catalysts and the effects of microwave power, catalyst carriers, active component content, and space velocity on the dry reforming reaction were investigated. The Fe/(SiC·SiO₂) catalyst reached the steady temperature quickly, while the heating process of Fe/(Al₂O₃·SiC) involves three stages with a small heating rate and it took longer to reach the steady temperature. The performance of Fe/(SiC·SiO₂) was obviously better than that of Fe/(Al₂O₃·SiC). And it was observed that about 95% conversions of reactants were achieved with Fe content of 12 wt%, space velocity of 200 h^?1, and microwave power of 90 W/g. Thus, Fe-based catalysts supported on foam ceramics exhibit good performance in the microwave CH₄CO₂ reforming reaction.     

Hydrogen production from carbon dioxide reforming of methane over highly active and stable MgO promoted Co–Ni/γ-Al2O3 catalyst

CoNi/Al₂O₃ and MgCoNi/Al₂O₃ catalysts are investigated for hydrogen production from CO₂ reforming of CH₄ reaction at the gas hourly space velocity of 40,000 mL g⁻¹ h⁻¹. The MgO promoted CoNi/Al₂O₃ catalyst shows much higher conversions (97% for CO₂ and 95% for CH₄ at 850 °C) than the CoNi/Al₂O₃ catalyst. In addition, the stability is maintained for 200 h in CO₂ reforming of CH₄. The outstanding catalytic activity and stability of the MgO promoted CoNi/Al₂O₃ catalyst is mainly due to the basic nature of MgO, an intimate interaction between Ni and the support, and rapid decomposition/dissociation of CH₄ and CO₂, resulting in preventing coke formation in CO₂ reforming of CH₄.     

Catalytic CO2 reforming of CH4 over Cr-promoted Ni/char for H2 production

The objective of the study is to investigate the catalytic performance of Cr-promoted Ni/char in CO₂ reforming of CH₄ at 850 °C. The char obtained from the pyrolysis of a long-flame coal at 1000 °C was used as the support. The catalysts were prepared by incipient wetness impregnation methods with different metal precursor doping sequence. The characterization of the composite catalysts was evaluated by XRD, XPS, SEM-EDS, TEM, H₂-TPR, CO₂-TPD, CH₄-TPSR, and CO₂-TPO. The results indicate that the catalyst prepared by co-impregnation of Ni and Cr possess higher activity than those by sequential impregnation. The optimal loading of Cr on 5 wt% Ni/char is 7.8 wt‰. Moreover, the molar feed ratio of CH₄/CO₂ has a considerable effect on both the stability and the activity of Cr–Ni/char. The main effect of Cr is the great enhance of the adsorption to CO₂. It is interesting that the conversions of CH₄ and CO₂ over Cr-promoted Ni/char and Ni/char decrease initially, following by a steady rise as the reaction proceeds with time-on-stream (TOS). In addition, cyclic tests were conducted and no distinct deterioration in the catalytic performance of the catalysts was observed. On the basis of the obtained results, nickel carbide was speculated to be the active species which was formed during the CO₂ reforming of CH₄ reaction.     

Conversion of carbon dioxide and methane in biomass synthesis gas for liquid fuels production

The premise of this research is to find whether methane (CH₄) and carbon dioxide (CO₂) produced during biomass gasification can be converted to carbon monoxide (CO) and hydrogen (H₂). Simultaneous steam and dry reforming was conducted by selecting three process parameters (temperature, CO₂:CH₄, and CH₄:steam ratios). Experiments were carried out at three levels of temperature (800 °C, 825 °C and 850 °C), CO₂:CH₄ ratio (2:1, 1:1 and 1:2), and CH₄:steam ratio (1:1, 1:2 and 1:3) at a residence time of 3.5 × 10³ g_cat min/cc using a custom mixed gas that resembles biomass synthesis gas, over a commercial catalyst. Experiments were conducted using a Box-Behnken approach to evaluate the effect of the process variables. The average CO and CO₂ selectivities were 68% and 18%, respectively, while the CH₄ and CO₂ conversions were about 65% and 48%, respectively. The results showed optimum conditions for maximum CH₄ conversion was at 800 °C, CO₂:CH₄ ratio and CH₄:steam ratios of 1:1.     

Syngas production via plasma photocatalytic reforming of methane with carbon dioxide

Anthropogenic emission of CH₄ and CO₂ contributes for most of global warming. Hence, simultaneous conversion of CH₄ and CO₂ into syngas (dry reforming of methane) can be a promising way to alleviate climate change. In this work, we developed a series of perovskite-type photocatalysts, based on LaFeO₃ with various calcination temperatures to combine with a spark discharge reactor to form a hybrid plasma photocatalysis reactor. The hybrid reactor is applied for dry reforming of methane to investigate the syngas generation rate and to reveal possible interactions between plasma and photocatalyst. Results show that LFO600-packed bed has the best CH₄ and CO₂ conversions and syngas generation efficiency of 53.6%, 40.0% and 18.4 mol/kWh, respectively. The enhancement of syngas generation rate can be attributed to synergies between LFO and plasma. Furthermore, changing calcination temperature of photocatalyst also leads to variable characteristics of photocatalyst and hence plasma photocatalysis performance for syngas production.     

Hydrogen production from CH4 dry reforming over Sc promoted Ni / MCM-41

The activity of Ni supported on MCM-41 catalyst with/without scandium promoter was investigated for hydrogen production. The performance of the catalysts with different Sc loadings (0.00, 0.10, 0.25, 0.50, 0.75, 1.00 and 3.00 wt%) was examined. N₂ adsorption-desorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for the characterization of the catalytic materials. The prepared catalysts were tested in dry reforming of methane. The effect of Sc addition on activity, hydrogen yield, H₂/CO ratio and stability are discussed. CH₄ and CO₂ conversions were measured under atmospheric pressure at 800 °C. Low Sc loading (<0.75 wt%) showed a positive effect on H₂ yield, CH₄ and CO₂ conversions. Addition of Sc strengthened the interaction of Ni with support and also increased the basicity which in turn affected the amount of CO₂ adsorbed on the surface of the catalyst. Notably, promoting with Sc almost suppressed the carbon formation leading to outstanding catalytic stability; thus 17% carbon deposition reduction was attained. The effect of different reaction temperatures, GHSV and CH₄:CO₂ ratio was also investigated.     

Ultracompact methane steam reforming reactor based on microwaves susceptible structured catalysts for distributed hydrogen production

Hydrogen is a potential green energy vector. Since the heating of the reforming processes commonly used for its production is obtained by burning hydrocarbons, it has a substantial CO₂ footprint. One of the most critical aspects in the methane steam reforming (MSR) reaction is the heat transfer to the catalytic volume, due to the high heat fluxes required to obtain high methane conversions. Consequently, the reactor has complex geometries, along with the heating medium being characterized by temperatures higher than 1000 °C; expensive construction materials and high reaction volumes are therefore needed, resulting in slow thermal transients. These aspects increase the costs (both operative and fixed) as well as cause a decrease in the whole process efficiency. The heat transfer limitations due to the endothermicity of methane steam reforming reaction could be effectively overcome by microwave (MW) heating. This heating technique, that depends only on the dielectric properties of the materials, can result in an efficient and faster method for transferring heat directly to the catalyst, thus generating the heat directly inside the catalytic volume. In this work, Ni-based catalysts, differing from each other by the Ni loading (7 and 15 wt% with respect to the washcoat) were prepared. The catalysts were characterized by means of several techniques and tested in the MW-assisted methane steam reforming reaction. Furthermore, the energy balance of the entire process was performed to calculate the energy efficiency, making a preliminary evaluation of its feasibility in distributed hydrogen production also possible. The results of the preliminary tests showed that the prepared structured catalysts are very susceptible to the MW radiation, and that in the presence of the MSR reaction, it is possible to make the system reach a temperature of 900 °C. In the same tests, the CH₄ conversion showed a good approach to the thermodynamic equilibrium values starting at temperatures of about 800 °C at a value of gas hourly space velocity (GHSV) of about 5000 h^?1. The energy efficiency of the lab-scale system, calculated as the ratio among the energy absorbed by the system and the energy supplied by the microwaves, was about 50%. Future studies will deal with the microwave reactor optimization, aiming at the increase of the energy efficiency of the system, as well as to obtain a higher CH₄ conversion at lower temperatures and increase the H₂ yield and selectivity.     

Rh promoted and ZrO2/Al2O3 supported Ni/Co based catalysts: High activity for CO2 reforming,steam–CO2 reforming and oxy–CO2 reforming of CH4

Ni (2.5 wt%) and Co (2.5 wt%) supported over ZrO₂/Al₂O₃ were prepared by following a hydrolytic co-precipitation method. The synthesized catalysts were further promoted by Rh incorporation (0.01–1.00 wt%) and tested for their catalytic performance for dry CO₂ reforming, combined steam–CO₂ reforming and oxy–CO₂ reforming of methane for production of syngas. The catalysts were characterized by using N₂ physical adsorption, XRD, H₂–TPR, SEM, CO₂–TPD, NH₃–TPD, TEM and TGA. The results revealed that ZrO₂ phase was in crystalline form in the catalysts along with amorphous Al oxides. Ni and Co were confirmed to be in their respective spinel phases that were reducible to metallic form at 800 °C under H₂. Ni and Co were well dispersed with their nano-crystalline nature. The catalyst with 0.2% loading of Rh showed superior performance in the studied reactions for reforming of methane. This catalyst also showed good coke resistance ability for dry CO₂ reforming reaction with 3.8 wt% of carbon formation during the reaction as compared to 11.6 wt% carbon formation over the catalyst without Rh. The catalyst performance was stable throughout the reaction time for CH₄ conversions, irrespective of carbon formation with slight decline (～1%) in CO₂ conversion. For dry CO₂ reforming reaction, this catalyst showed good conversion for both CH₄ and CO₂ (67.6% and 71.8% respectively) with a H₂/CO ratio of 0.84, while for the Oxy-CO₂ reforming reaction, the activity was superior with CH₄ and CO₂ conversions (73.7% and 83.8% respectively) and H₂/CO ratio of 1.05.     

Biogas upgrade to syn-gas (H2-CO) via dry and oxidative reforming

Fuel reforming processes are primarily used to generate hydrogen for fuel cells and in automotive internal combustion engines to improve combustion characteristics and emissions. In this study, biogas is used as the fuel source for the reforming process as it has desirable properties of being both renewable and clean. Two reforming processes (dry reforming and combined dry/oxidative reforming) are studied. Both processes are affected by the gas stream temperature and reactor space velocity with the second process being affected by O₂/CH₄ ratio as well. Our results imply that oxidative reforming is the dominant process at low exhaust temperatures. This provides heat for the dry reforming of biogas and the overall reforming is exothermic. Increase in O₂/CH₄ ratio at low temperature promotes hydrogen production. At high exhaust temperatures (>600 °C), dry reforming of biogas is dominant and the overall reaction is net endothermic.     

Ni/MgAl2O4 catalyst for low-temperature oxidative dry methane reforming with CO2

Oxidative dry reforming of methane has been performed for 100 h on stream using Ni supported on MgAl₂O₄ spinel at different loadings at 500–700 °C, CO₂/CH₄ molar ratio of 0.76, and variable O₂/CH₄ molar ratio (0.12–0.47). Syngas with an H₂/CO ratio of 1.5–2.1 has been produced by manipulating reforming feed composition and temperature. The developed oxidative dry reforming process allowed high CH₄ conversion at all conditions, while CO₂ conversion decreased significantly with the lowering of the reforming temperature and increasing O₂ concentration. When considering both greenhouse gas conversions and H₂/CO ratio enhancement, the optimal reforming condition should be assigned to 550 °C and O₂/CH₄ molar ratio of 0.47, which delivered syngas with H₂/CO ratio of 1.5. Coke-free operation was also achieved, due to the combustion of surface carbon species by oxygen. The 3.4 wt% Ni/MgAl₂O₄ catalyst with a mean Ni nanoparticle diameter of 9.8 nm showed stable performance during oxidative dry reforming for 100 h on stream without deactivation by sintering or coke deposition. The superior activity and stability of MgAl₂O₄ supported Ni catalyst shown during reaction trials is consistent with characterization results from XRD, TPR, STEM, HR-STEM, XPS, and CHNS analysis.     

Potential of Ni supported on KH zeolite catalysts for carbon dioxide reforming of methane

The catalytic activity of Ni on a series of catalysts supported on the synthesized KH zeolite for the CO₂ reforming of methane has been investigated. The KH zeolite supports were previously synthesized via silatrane and alumatrane precursors using the sol–gel process and hydrothermal microwave treatment. Eight percent Ni was impregnated onto the synthesized KH zeolites, which have different morphologies: called dog-bone, flower, and disordered shapes. The prepared Ni/KH zeolites were tested for their catalytic activity at 700 °C, at atmospheric pressure, and at a CH₄/CO₂ ratio of 1. The results showed that Ni supported on dog-bone and flower-shaped KH zeolites provided better activity than that of disordered KH zeolite due to higher CH₄ and CO₂ conversions, a higher H₂ production, and a smaller amount of coke formation on the catalyst surface. Furthermore, the stability of the Ni/KH zeolite was greatly superior to that of Ni supported on alumina and clinoptiolite catalysts after 65 h on stream.     

Sorption enhanced reaction process for direct production of fuel-cell grade hydrogen by low temperature catalytic steam-methane reforming

New experimental data are reported to demonstrate that a sorption enhanced reaction (SER) concept can be used to directly produce fuel-cell grade H₂ (<20 ppm CO) by carrying out the catalytic, endothermic, steam-methane reforming (SMR) reaction (CH₄ + 2H₂O ↔ CO₂ + 4H₂) in presence of a CO₂ selective chemisorbent such as K₂CO₃ promoted hydrotalcite at reaction temperatures of 520 and 550 °C, which are substantially lower than the conventional SMR reaction temperatures of 700-800 °C. The H₂ productivity of the sorption enhanced reactor can be large, and the conversion of CH₄ to H₂ can be very high circumventing the thermodynamic limitations of the SMR reaction due to the application of the Le Chetalier's principle in the SER concept. Mathematical simulations of a cyclic two-step SER concept showed that the H₂ productivity of the process (moles of essentially pure H₂ produced per kg of catalyst-chemisorbent admixture in the reactor per cycle) is much higher at a reaction temperature of 590 °C than that at 550 or 520 °C. On the other hand, the conversion of feed CH₄ to high purity H₂ product is relatively high (>99+%) at all three temperatures. The conversion is much higher than that in a conventional catalyst-alone reactor at these temperatures, and it increases only moderately (<1%) as the reaction temperature is increased from 520 to 590 °C. These results are caused by complex interactions of four phenomena. They are (a) favorable thermodynamic equilibrium of the highly endothermic SMR reaction at the higher reaction temperature, (b) faster kinetics of SMR reaction at higher temperatures, (c) favorable removal of CO₂ from the reaction zone at lower temperatures, and (d) higher cyclic working capacity for CO₂ chemisorption at higher temperature.     

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.     

Kinetics and mechanistic studies of methane dry reforming over Ca promoted 1Co–1Ce/AC-N catalyst

The mechanism and kinetic features of dry reforming with methane (DRM) over Ca promoted 1Co–1Ce/AC-N catalyst was investigated. The mechanistic pathway studies have conducted by FTIR and XPS analysis, structure-activity correlations demonstrated the CH₄ and CO₂ could adsorb on catalyst active sites and generate intermediate CH_x, OH and CH_xO, continue to generate CO and H₂ and then desorbed from active sites. Moreover, CH₄ could also oxidized by Ce⁴⁺ and CO₂ reduced by Ce³⁺, the same content of Ce⁴⁺ and Ce³⁺ on promoted catalyst greatly improved the reaction rate. The kinetic of dry reforming with methane was examined for temperature between 650 and 850 at 800 °C. The research was carried out by changing the CH₄/CO₂ ratios between 0.3 and 3.0. The obtained experiment data were fitted by three typical kinetic models (Power Law, Eley-Rideal and Langmuir-Hinshelwood), the fitting results demonstrated that the best prediction of reforming rates can provided by Langmuir-Hinshelwood model for the reaction temperatures between 650 and 800 °C. Moreover, activation energies of methane and carbon dioxide consumption were ?117 and ?47 kJ/mol, indicating that much higher energy barrier is needed for methane activation compared to carbon dioxide.