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.     

Effects of modifying Ni/Al2O3 catalyst with cobalt on the reforming of CH4 with CO2 and cracking of CH4 reactions

Alumina supported nickel (Ni/Al₂O₃), nickel–cobalt (Ni–Co/Al₂O₃) and cobalt (Co/Al₂O₃) catalysts containing 15% metal were synthesized, characterized and tested for the reforming of CH₄ with CO₂ and CH₄ cracking reactions. In the Ni–Co/Al₂O₃ catalysts Ni–Co alloys were detected and the surface metal sites decreased with decrease in Ni:Co ratio. Turnover frequencies of CH₄ were determined for both reactions. The initial turnover frequencies of reforming (TOF_DRM) for Ni–Co/Al₂O₃ were greater than that for Ni/Al₂O₃, which suggested a higher activity of alloy sites. The initial turnover frequencies for cracking (TOF_CRK) did not follow this trend. The highest average TOF_DRM, H₂:CO ratio and TOF_CRK were observed for a catalyst containing a Ni:Co ratio of 3:1. This catalyst also had the maximum carbon deposited during reforming and produced the maximum reactive carbon during cracking. It appeared that carbon was an intermediate product of reforming and the best catalyst was able to most effectively crack CH₄ and oxidize carbon to CO by CO₂.     

Ni/CeO2 catalysts with high CO2 methanation activity and high CH4 selectivity at low temperatures

CO₂ methanation was performed over 10 wt%Ni/CeO₂, 10 wt%Ni/α-Al₂O₃, 10 wt%Ni/TiO₂, and 10 wt%Ni/MgO, and the effect of support materials on CO₂ conversion and CH₄ selectivity was examined. Catalysts were prepared by a wet impregnation method, and characterized by BET, XRD, H₂-TPR and CO₂-TPD. Ni/CeO₂ showed high CO₂ conversion especially at low temperatures compared to Ni/α-Al₂O₃, and the selectivity to CH₄ was very close to 1. The surface coverage by CO₂-derived species on CeO₂ surface and the partial reduction of CeO₂ surface could result in the high CO₂ conversion over Ni/CeO₂. In addition, superior CO methanation activity over Ni/CeO₂ led to the high CH₄ selectivity.     

Catalytic conversion of CH4 and CO2 to synthesis gas on Ni/SiO2 catalysts containing Gd2O3 promoter

A series of Ni/SiO₂ catalysts containing different amounts of Gd₂O₃ promoter was prepared, characterized by H₂-adsorption and XRD, and used for carbon dioxide reforming of methane (CRM) and methane autothermal reforming with CO₂ + O₂ (MATR) in a fluidized-bed reactor. The results of pulse surface reactions showed that Ni/SiO₂ catalysts containing Gd₂O₃ promoter could increase the activity for CH₄ decomposition, and Raman analysis confirmed that reactive carbon species mainly formed on the Ni/SiO₂ catalysts containing Gd₂O₃ promoter. In this work, it was found that methane activation and reforming reactions proceeded according to different mechanisms after Gd₂O₃ addition due to the formation of carbonate species. In addition, Ni/SiO₂ catalysts containing Gd₂O₃ promoter demonstrated higher activity and stability in both CRM and MATR reactions in a fluidized bed reactor than Ni/SiO₂ catalysts without Gd₂O₃ even at a higher space velocity.     

Y2O3-promoted NiO/SBA-15 catalysts highly active for CO2/CH4 reforming

A series of Y₂O₃-promoted NiO/SBA-15 (9 wt% Ni) catalysts (Ni:Y weight ratio = 9:0, 3:1, 3:2, 1:1) were prepared using a sol–gel method. The fresh as well as the catalysts used in CO₂ reforming of methane were characterized using N₂-physisorption, XRD, FT-IR, XPS, UV, HRTEM, H₂-TPR, O₂-TPD and TG techniques. The results indicate that upon Y₂O₃ promotion, the Ni nanoparticles are highly dispersed on the mesoporous walls of SBA-15 via strong interaction between metal ions and the HO–Si-groups of SBA-15. The catalytic performance of the catalysts were evaluated at 700 °C during CH₄/CO₂ reforming at a gas hourly space velocity of 24 L g_cat⁻¹ h⁻¹(at 25 ^°C and 1 atm) and CH₄/CO₂molar ratio of 1. The presence of Y₂O₃ in NiO/SBA-15 results in enhancement of initial catalytic activity. It was observed that the 9 wt% Y–NiO/SBA-15 catalyst performs the best, exhibiting excellent catalytic activity, superior stability and low carbon deposition in a time on stream of 50 h.     

Carbon dioxide reforming of methane to synthesis gas over Ni/Si3N4 catalysts

Silicon nitride supported nickel catalyst prepared by impregnation using nickel nitrate solution was employed for the carbon dioxide reforming of methane. The catalyst was tested at 800 °C under atmospheric pressure. The influences of Ni loading and calcination temperature on the catalytic performance were investigated. It was found that the nickel loading and calcination temperature strongly influenced the catalytic performance. Over the 7 wt. % Ni/Si₃N₄ catalyst calcined at 400 °C, the conversions of CH₄ and CO₂ can achieve 95% and 91%, respectively. Appropriate interaction between the metal and the basic support makes the catalyst more resistant to sintering and coking, and thus an excellent stability.     

Combined catalytic partial oxidation and CO2 reforming of methane over ZrO2-modified Ni/SiO2 catalysts using fluidized-bed reactor

Nickel on zirconium-modified silica was prepared and tested as a catalyst for reforming methane with CO₂ and O₂ in a fluidized-bed reactor. A conversion of CH₄ near thermodynamic equilibrium and low H₂/CO ratio (1<H₂/CO<2) were obtained without catalyst deactivation during 10 h, in a most energy efficient and safe manner. A weight loading of 5 wt% zirconium was found to be the optimum. The catalysts were characterized using X-ray diffraction (XRD), H₂-temperature reaction (H₂-TPR), CO₂-temperature desorption (CO₂-TPD) and transmission election microscope (TEM) techniques. Ni sintering was a major reason for the deactivation of pure Ni/SiO₂ catalysts, while Ni dispersed highly on a zirconium-promoted Ni/SiO₂ catalyst. The different kinds of surface Ni species formed on ZrO₂-promoted catalysts might be responsible for its high activity and good resistance to Ni sintering.     

Au-doped Ni/GDC as a new anode for SOFCs operating under rich CH4 internal steam reforming

In the present work we describe a Solid Oxide Fuel Cell (SOFC) that comprises a Ni/GDC cermet anode, doped with a potentially commercially viable concentration of gold nano-particles. Specifically, gold was applied prior to anode sintering via the deposition–precipitation method. This procedure resulted in a SOFC that allowed carbon tolerant operation at T = 850 °C under fuel rich internal steam reforming of methane, with a stable power density of 0.41 W cm⁻² at 810 mV for over 200 h.     

Carbon deposition behavior of a Co–Ni aerogel catalyst in CH4 oxy-CO2 reforming using various types of reactors

Carbon deposition behavior of a Co–Ni aerogel catalyst in CH₄ oxy-CO₂ reforming is investigated using a deactivation method in three types of reactors including a magnetic field assisted fluidized bed (MAFB) reactor, a conventional fluidized bed reactor and a fixed bed reactor. The spent catalysts are analyzed by TG/DSC and FESEM. It is found that the reactor influences the amount as well as type of carbon species on the spent catalysts. The amount of carbon on the spent catalyst in the MAFB reactor is 11.7 wt.%, which is 10.8 wt.% and 2.6 wt.% less than those in the fixed bed and conventional fluidized bed reactors. Fluidization behavior analysis reveals that agglomerate and bubble size of the catalyst are obviously decreased with the application of the MAFB, which should be accounted for the enhanced carbon resistance of the reactor.     

Low metal content Co and Ni alumina supported catalysts for the CO2 reforming of methane

Low metal content Co and Ni alumina supported catalysts (4.0, 2.5 and 1.0 wt% nominal metal content) have been prepared, characterized (by ICP-OES, TEM, TPR-H₂ and TPO) and tested for the CO₂ reforming of methane. The objective is to optimize the metal loading in order to have a more efficient system. The selected reaction temperature is 973 K, although some tests at higher reaction temperature have been also performed. The results show that the amount of deposited carbon is noticeably lower than that obtained with the Co and Ni reference catalysts (9 wt%), but the CH₄ and CO₂ conversions are also lower. Among the catalysts tested, the Co(1) catalyst (the value in brackets corresponds to the nominal wt% loading) is deactivated during the first minutes of reaction because CoAl₂O₄ is formed, while Ni(1) and Co(2.5) catalysts show a high specific activity for methane conversion, a high stability and a very low carbon deposition.     

Ni-based catalysts for reforming of methane with CO2

Ni catalysts supported on different carriers like δ,θ-Al₂O₃, MgAl₂O₄, SiO₂–Al₂O₃ and ZrO₂–Al₂O₃ were prepared. The solids were characterized by chemical analysis, N₂ adsorption–desorption isotherms, X-ray powder diffraction, UV–vis diffuse reflectance spectroscopy, temperature-programmed reduction, high-resolution transmission electron microscopy and temperature-programmed oxidation. The catalytic properties of the samples were evaluated in the reaction of reforming of methane with CO₂ at 923 K. It was shown that this kind of support greatly affects the structure and catalytic performance of the catalysts. Ni catalyst supported on MgAl₂O₄ showed the highest activity and stability due to the presence of small well dispersed Ni particles with size of 5.1 nm. It was shown that the lowest activity of Ni catalyst supported on SiO₂–Al₂O₃ oxide was caused by the agglomeration of nickel particles and formation of filamentous carbon under reaction conditions detected by the high resolution transmission electron microscopy.     

CNT/PDMS composite membranes for H2 and CH4 gas separation

Polydimethylsiloxane (PDMS) composites with different weight amounts of multi-walled carbon nanotubes (MWCNT) were synthesised as membranes to evaluate their gas separation properties. The selectivity of the membranes was investigated for the separation of H₂ from CH₄ gas species. Membranes with MWCNT concentrations of 1% increased the selectivity to H₂ gas by 94.8%. Furthermore, CH₄ permeation was almost totally blocked through membranes with MWCNT concentrations greater than 5%. Vibrational spectroscopy and X-ray photoelectron spectroscopy techniques revealed that upon the incorporation of MWCNT a decrease in the number of available Si–CH₃ and Si–O bonds as well as an increase in the formation of Si–C bonds occurred that initiated the reduction in CH₄ permeation. As a result, the developed membranes can be an efficient and low cost solution for separating H₂ from larger gas molecules such as CH₄.     

Role of CO2 in the CH4 oxidation and H2 formation during fuel-rich combustion in O2/CO2 environments

The effect of CO₂ reactivity on CH₄ oxidation and H₂ formation in fuel-rich O₂/CO₂ combustion where the concentrations of reactants were high was studied by a CH₄ flat flame experiment, detailed chemical analysis, and a pulverized coal combustion experiment. In the CH₄ flat flame experiment, the residual CH₄ and formed H₂ in fuel-rich O₂/CO₂ combustion were significantly lower than those formed in air combustion, whereas the amount of CO formed in fuel-rich O₂/CO₂ combustion was noticeably higher than that in air. In addition to this experiment, calculations were performed using CHEMKIN-PRO. They generally agreed with the experimental results and showed that CO₂ reactivity, mainly expressed by the reaction CO₂ + H → CO + OH (R1), caused the differences between air and O₂/CO₂ combustion under fuel-rich condition. R1 was able to advance without oxygen. And, OH radicals were more active than H radicals in the hydrocarbon oxidation in the specific temperature range. It was shown that the role of CO₂ was to advance CH₄ oxidation during fuel-rich O₂/CO₂ combustion. Under fuel-rich combustion, H₂ was mainly produced when the hydrocarbon reacted with H radicals. However, the hydrocarbon also reacted with the OH radicals, leading to H₂O production. In fact, these hydrocarbon reactions were competitive. With increasing H/OH ratio, H₂ formed more easily; however, CO₂ reactivity reduced the H/OH ratio by converting H to OH. Moreover, the OH radicals reacted with H₂, whereas the H radicals did not reduce H₂. It was shown that OH radicals formed by CO₂ reactivity were not suitable for H₂ formation. As for pulverized coal combustion, the tendencies of CH₄, CO, and H₂ formation in pulverized coal combustion were almost the same as those in the CH₄ flat flame.     

CO2 reforming of methane over Pt-Ni/Al2O3 catalysts: Effects of catalyst composition, and water and oxygen addition to the feed

A series of Pt-Ni bimetallic catalysts supported on δ-Al₂O₃ to be used in carbon dioxide reforming of methane was prepared and tested with the objective of optimizing the Ni/Pt metal composition to obtain high activity and stability. Selected catalyst samples, before and after reaction, were characterized by XRD, XPS, TGA/DTA and SEM-EDS. The activity results showed that the catalytic performance of bimetallic Pt-Ni samples strongly depended on the metal loadings and Ni/Pt loading ratio. Among all the catalysts, 0.3%Pt-10%Ni/Al₂O₃, which has the lowest Ni/Pt ratio, exhibited the highest catalytic activity and stability. The combined characterization and catalyst performance tests results reveal that low Ni/Pt molar loading ratio of 0.3%Pt-10%Ni/Al₂O₃ sample led to a relatively easy reduction of nickel oxide species and smaller nano-sized nickel particles having better dispersion caused by the intimate interaction between Pt and Ni sites in the closed vicinity. The changes in the catalysts’ activity and stability under the presence of an additional oxygen source were determined through addition of small amounts of either oxygen or water vapor to the feed stream. The results of the combined dry reforming and partial oxidation tests strongly indicated a change in surface reaction mechanism depending on the Pt load and Ni/Pt ratio of the catalysts. 0.3Pt-10Ni was capable of operating under a variety of feed conditions without significant deactivation suggesting that the catalyst is very promising for synthesis gas production for gas-to-liquid technology.     

Reduction characteristics of CuFe2O4 and Fe3O4 by methane; CuFe2O4 as an oxidant for two-step thermochemical methane reforming

The reduction characteristics of CuFe₂O₄ and Fe₃O₄ by methane at 600–900 °C were determined in a thermogravimetric analyzer for the purpose of using CuFe₂O₄ as an oxidant of two-step thermochemical methane reforming. It was found that the addition of Cu to Fe₃O₄ largely affected the reduction kinetics and carbon formation in methane reduction. In the case of CuFe₂O₄, the reduction kinetics was found to be faster than that of Fe₃O₄. Furthermore, carbon deposition and carbide formation from methane decomposition were effectively inhibited. In case of Fe₃O₄, Fe metal formed from Fe₃O₄ decomposed methane catalytically, that lead to the formation of graphite and Fe₃C phases. It is deduced that Cu in CuFe₂O₄ enhanced reduction kinetics, decreased reduction temperature and prevented carbide and graphite formation. Additionally, methane conversion and CO selectivity in the syngas production step with CuFe₂O₄ were in the range of 33.5–55.6% and 54.9–59.6%, respectively.     

Photocatalytic reforming of ethanol to H2 and CH4 over ZnSn(OH)6 nanocubes

ZnSn(OH)₆ nanocubes (ZHS) were synthesized by solvothermal method and then characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), N₂ sorption (BET surface area), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Photocatalytic reforming of ethanol for H₂ production over ZHS samples were investigated and compared under different reaction conditions. The results indicated that the cubes were formed by the adsorption of small irregular ZHS particles via the Ostwald ripening process. ZHS showed high photoactivity for reforming ethanol to H₂ and CH₄. The H₂ evolution rate of ZHS was found more susceptible to the crystallinity of the samples than the surface area, and could be significantly enhanced by loading with Pt.     

Effect of hydrogen on H2/CH4 flame structure of MILD combustion using the LES method

Large eddy simulation (LES) method is employed to investigate the effect of the hydrogen content of fuel on the H₂/CH₄ flame structure under the moderate or intense low-oxygen dilution (MILD) condition. The turbulence–chemistry interaction of the numerically unresolved scales is modelled using the PaSR method, where the full mechanism of GRI-2.11 represents the chemical reactions. The influence of hydrogen concentration on the flame structure is studied using the profiles of temperature, CH₂O and OH mass fractions and the diffusion profiles of un-burnt fuel through the flame front. Furthermore, more details are investigated by contours of OH, HCO and CH₂O radicals in an area near the nozzle exit zone. Results show that increasing the hydrogen content of fuel reinforces the MILD combustion zone and increases the peak value of the flame temperature and OH mass fraction. This increment also increases the flame thickness and reduces the OH oscillations and diffusion of the un-burnt fuel through the flame front.     

The effect of impregnation strategy on methane dry reforming activity of Ce promoted Pt/ZrO2

Dry reforming of methane has been studied over Pt/ZrO₂ catalysts promoted with Ce for different temperatures and feed compositions. The influence of the impregnation strategy and the cerium amount on the activity and stability of the catalysts were investigated. The results have shown that introduction of 1 wt.% Ce to the Pt/ZrO₂ catalyst via coimpregnation method led to the highest catalytic activity and stability. 1 wt.%Ce–1 wt.%Pt/ZrO₂ catalyst prepared by sequential impregnation displayed inferior CH₄ and CO₂ conversion performances with lowest H₂/CO production ratios. 1 wt.%Ce–1 wt.%Pt/ZrO₂ catalyst prepared by coimpregnation showed the highest activity even for the feed with high CH₄/CO₂ ratio. The reason for high activity was explained by the intensive interaction between Pt and Ce phases for coimpregnated sample, which had been verified by X-ray photoelectron spectroscopy and Energy Dispersive X-Ray analyses. Strong and extensive Pt–Ce surface interaction results in an increase in the number of Ce³⁺ sites and enhances the dispersion of Pt.     

Autothermal reforming of methane over nickel catalysts supported on nanocrystalline MgAl2O4 with high surface area

In this paper autothermal reforming of methane (ATR) was carried out over MgAl₂O₄ supported Ni catalysts with various Ni loadings. MgAl₂O₄ spinel with high specific surface area, as nanocrystalline carrier for nickel catalysts was synthesized by co-precipitation method with the addition of pluronic P123 triblock copolymer as surfactant. The prepared samples were characterized by XRD, BET, TEM, SEM, TPR and TPH techniques. The results demonstrated that methane conversion is significantly increased with increasing the Ni content and methane conversion of 15% Ni/MgAl₂O₄ was higher than that of other catalysts in all operation temperatures. Furthermore the influences of H₂O/CH₄, and O₂/CH₄ molar ratio in feed and GHSV on activity of 5% Ni/MgAl₂O₄ catalyst were investigated.     

Hydrogen production by oxidative steam reforming of methanol over Ni/CeO2–ZrO2 catalysts

Single ZrO₂ and mixed CeO₂-ZrO₂ oxides with different CeO₂/ZrO₂ ratios were prepared by the sol-gel method and the CeO₂ by precipitation. The prepared support were impregnated with an aqueous solution of NiCl₂·6H₂O at an appropriate concentration to yield 3 wt.% of nickel respectively in the catalysts. Catalytic materials were characterized by BET (N₂ adsorption-desorption), SEM-EDS, XRD and TPR. The oxidative steam reforming of methanol (OSRM) reaction was investigated on these catalysts for H₂ production as a function of temperature. Depending of the CeO₂/ZrO₂ ratio; the catalysts composition has a significant influence on the surface area (BET), reduction properties and methanol conversion. XRD patterns of the Ni-base catalysts showed well defined diffraction peaks of the metallic Ni except on the Ni/CeO₂ catalyst, suggesting that on this sample all of the active phase was highly dispersed. Ni/Ceria-rich catalysts were vastly active for OSRM, giving a total CH₃OH conversion at 325 °C with GHSV = 0.3 × 10⁵ h⁻¹. They also showed close selectivity toward H₂, with high selectivity to CO₂ in all range of temperatures, this suggests that the reverse WGS reaction does not occur on these samples. It seems that the nickel is the phase mainly responsible of hydrogen production although the CeO₂/ZrO₂ support reduces the CO formation.