Catalytic performance of Samarium-modified Ni catalysts over Al2O3–CaO support for dry reforming of methane

Mesoporous calcina-modified alumina (Al₂O₃–CaO) support was produced through the simple and economical co-precipitation method, then nickel (Ni, 10 wt%) and samarium (Sm, 3 wt%) ions loaded by two-solvent impregnation and one-pot strategies. The unpromoted/samarium-promoted catalysts were evaluated using X-ray Diffraction (XRD), High-Resolution Transmission Electron Microscopy (HR-TEM), nitrogen adsorption-desorption, Temperature Programmed Oxidation/Reduction (TPR/TPO), and Field Emission Electron Scanning Microscopy (FE-SEM) methods, then investigated in methane dry reforming. The results revealed that with adding samarium to Ni catalyst through impregnation method, the average Ni crystallite size and specific surface area decreased from 11.5 to 5.75 nm and from 76.08 to 30.9 m²/g, respectively; as a result, the catalytic activity increased from about 50% to 68% at 700 °C. Furthermore, the TPO and FE-SEM tests indicated the formation of carbon with nanotube nature on the catalyst surface.     

Ni–Re alloy catalysts on Al2O3 for methane dry reforming

Methane reforming with CO₂ is still of great interest due to growing demand creating a continuous need for new hydrogen sources. The main difficulty in this reaction is the deactivation of the catalyst due to the formation of carbon deposits on its surface. Herein, a series of commercial nickel catalysts supported on α-Al₂O₃ and modified with different amounts of rhenium (up to 4 wt%) was investigated. It was revealed that Re addition causes the formation of Ni–Re alloy during high temperature reduction, which was confirmed in deep XRD and STEM studies. The addition of Re positively influences not only the stability of the catalyst, but also increases its activity in the DRM reaction carried out in a Tapered Element Oscillating Microbalance (TEOM). The formation of Ni–Re alloy played a significant role in enhancing the properties of the catalyst.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over Ni/Al2O3–ZrO2 xerogel catalysts: Effect of calcination temperature of Al2O3–ZrO2 xerogel supports

Al₂O₃–ZrO₂ (AZ) xerogel supports prepared by a sol-gel method were calcined at various temperatures. Ni/Al₂O₃–ZrO₂ (Ni/AZ) catalysts were then prepared by an impregnation method for use in hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of calcination temperature of AZ supports on the catalytic performance of Ni/AZ catalysts in the steam reforming of LNG was investigated. Crystalline phase of AZ supports was transformed in the sequence of amorphous γ-Al₂O₃ and amorphous ZrO₂ → θ-Al₂O₃ and tetragonal ZrO₂ → (θ + α)-Al₂O₃ and (tetragonal + monoclinic) ZrO₂ → α-Al₂O₃ and (tetragonal + monoclinic) ZrO₂ with increasing calcination temperature from 700 to 1300 °C. Nickel oxide species were strongly bound to γ-Al₂O₃ and θ-Al₂O₃ in the Ni/AZ catalysts through the formation of solid solution. In the steam reforming of LNG, both LNG conversion and hydrogen composition in dry gas showed volcano-shaped curves with respect to calcination temperature of AZ supports. Nickel surface area of Ni/AZ catalysts was well correlated with catalytic performance of the catalysts. Among the catalysts tested, Ni/AZ1000 (nickel catalyst supported on AZ support that had been calcined at 1000 °C) with the highest nickel surface area showed the best catalytic performance. Well-developed and pure tetragonal phase of ZrO₂ in the AZ1000 support played an important role in the adsorption of steam and the subsequent spillover of steam from the support to the active nickel.     

Impact of ceria over WO3–ZrO2 supported Ni catalyst towards hydrogen production through dry reforming of methane

ZrO₂ supported Nickel catalyst, 9 wt%WO₃ -91 wt%ZrO₂ supported Nickel catalyst and ceria promoted 9 wt%WO₃-91 wt%ZrO₂ supported Nickel catalyst (5NixCe/WZr catalyst) is synthesized via wet impregnation and characterized by XRD, UV–vis, CO₂ -TPD, H₂ TPR-CO₂ TPD-H₂ TPR cycle, TPH, TPH followed by O₂ -TPO and CO₂ -TPD followed by O₂ -TPO. Due to limitation in surface re-oxidizing capability and shading of catalytic active sites by thermally stable carbonates; catalytic activity of unpromoted catalyst system is less. 5NixCe/WZr catalyst has extended CH₄ decomposition sites, additional basic sites (during the reaction) for CO₂ adsorption and excellent redox accompany (Ce ⁺⁴/Ce ⁺³, W+⁶/W ⁺⁴) for carbon oxidation and re-oxidizing capability of surface up to the pristine level. 2.5 wt% Ceria promotional addition is resulted into 78% H₂ yield constantly up to 420 min TOS. The carbon deposit over ceria promoted system (up to 2.5 wt%) is amorphous type, more easily/moderately reducible, oxidizable and removable.     

Dry reforming of methane over Ni/MgO–Al2O3 catalysts: Thermodynamic equilibrium analysis and experimental application

In this study, dry reforming of methane (DRM) employing a Ni/MgO–Al₂O₃ catalyst was undertaken to evaluate the effects of temperature (650, 700 and 750 °C), weight hourly space velocity (7.5, 15 and 30 L h⁻¹ g_cat⁻¹) and catalyst MgO content (3, 5 and 10 wt%) on catalytic activity and coke-resistance. The catalysts were prepared by the wet impregnation method and were characterized by wavelength dispersive X-ray fluorescence (XRF), N₂ physisorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR-H₂), temperature-programmed desorption (TPD-NH₃), H₂ chemisorption, thermogravimetric/derivative thermogravimetry analysis (TG/DTG) and scanning electron microscopy (SEM). The best conversions of methane (CH₄) and carbon dioxide (CO₂) and lower coke formation were obtained using higher temperatures, lower WHSV and 5 wt% MgO in the catalyst. The H₂/CO molar ratios obtained were within the expected range for the DRM reaction. The experimental yields of H₂ and CO differed from chemical equilibrium, mainly due to occurrence of the reverse water-gas shift reaction. Thermodynamic analysis of the reaction system, based on minimization of the Gibbs free energy, was performed in order to compare the experimental results with the optimal values for chemical equilibrium conditions, which has indicated that the DRM reaction was favored by higher temperature, lower pressure, and lower CH₄/CO₂ molar ratio.     

Co–Ni/WC-AC catalysts for dry reforming of methane: The role of Ni species

To improve the DRM reaction performance of the catalysts, a series of Co–Ni/WC-AC catalysts are prepared by impregnation using WC-AC as the support. The structural features of the fresh and spent catalysts are characterized by BET, XRD, H₂-TPR, XPS and TG. The results show that the introduction of Ni in the 20Co/WC-AC catalyst promotes the conversion of W species to WC. Further, WC enhances the interaction between the active metal and the support. Thus, the activity and sintering resistance of Co–Ni/WC-AC catalysts are improved. It is also found that the introduction of different ratios of Ni has a significant effect on the chemical environment (oxygen environment) on the catalyst surface.10Co–10Ni/WC-AC catalysts showed high surface O_α and O_β contents of 26% and 53%, respectively. The catalyst shows excellent catalytic performance. The conversion of CH₄ and CO₂ is stable at about 84% and 85% at 800 °C.     

Anti-sintering mesoporous Ni–Pd bimetallic catalysts for hydrogen production via dry reforming of methane

In this work, a series of mesoporous silica supported nickel or nickel-palladium catalysts were synthesized and performed in dry reforming of methane (DRM) reaction for producing syngas. Compared with the monometallic catalyst, the Ni–Pd bimetallic catalysts, especially synthesized by the OA-assisted route, exhibited promising yields of H₂ and CO in the catalytic DRM reaction, achieved at 63% and 69% over NiPd-SP-OA bimetallic catalyst at the reaction temperature of 700 °C, respectively. TEM image results confirmed that no obvious sintering phenomenon happened on spent NiPd-SP-OA bimetallic catalyst within 1550 min time-on-stream reaction. Based on the results of XRD, XPS and H₂-TPR, it could be known that the superior catalytic performance on NiPd-SP-OA catalyst were main ascribed to the smaller-sized Ni nanoparticles with a uniform metal dispersion and a larger fraction of exposed active sites (Ni⁰).     

Syngas production by the CO2 reforming of CH4 over Ni–Co–Mg–Al catalysts obtained from hydrotalcite precursors

The catalytic performance of the Ni, Co, Mg, and Al mixed-oxide solids, synthesized via hydrotalcite route, was investigated towards the dry reforming of methane for hydrogen production. The hydrotalcite structure was successfully obtained upon the synthesis. After calcination at 800 °C under an air flow, this structure was completely decomposed and the resulting oxides (Co_xNi_yMg_zAl₂800, x and y = 0; 1; 2; 3; 4, z = 2; 4, x + y + z = 6, x, y, and z are the molar ratios) were used as catalysts and were characterized using X-ray diffraction and Temperature-Programmed Reduction. The dry reforming of methane was carried out using a mixture of CH₄:CO₂ (1:1) after 2 h of reduction under an H₂ flow at 800 °C. Co₂Ni₂Mg₂Al₂800 showed the highest catalytic activity in the studied series, ascribable to an interaction between Ni and Co, which is optimal for such Co/Ni ratio. The post-reaction characterization of the catalytic samples by X-ray diffraction and Differential Scanning Calorimetry evidenced a better resistance towards carbon deposition for the catalysts where Co molar ratio is higher than Ni.     

Phosphate-modified Al2O3–ZrO2 supported Ni catalysts for efficient selective methanation of CO in H2-rich reformate gas

CO selective methanation can remove the CO in H₂-rich reformate gas to prevent the poisoning of Pt anode electrode in proton exchange membrane fuel cell. However, the methanation of CO₂ in H₂-rich gas consumes a lot of hydrogen, which greatly reduces the energy efficiency. In order to inhibit CO₂ methanation, mesostructured Al₂O₃–ZrO₂ was modified by different amounts of phosphate, and then was as Ni support. The structures and surface properties of Ni/Al₂O₃–ZrO₂ catalyst modified by phosphate were studied to reveal the effect of phosphate-modification on CO conversion and selectivity for CO methanation. It was found that the phosphate-modification inhibited the adsorption of CO₂, which increased the selective for CO methanation. But the modification with excess phosphate lessened active sites of Ni and weakened the adsorption of H₂ and CO, which decreased the activity of CO methanation.     

Natural gas reforming of carbon dioxide for syngas over Ni–Ce–Al catalysts

A series of Ni–Ce–Al composite oxides with various Ni molar contents were synthesized via the refluxed co-precipitation method and used for natural gas reforming of CO₂ (NGRC) for syngas production. The effect of Ni molar content, reaction temperature, feed gas ratio and gas hourly space velocity (GHSV) on the Ni–Ce–Al catalytic performance was investigated. The Ni₁₀CeAl catalyst was selected to undergo 30 h stability test and the conversion of CH₄ and CO₂ decreased by 2.8% and 2.6%, respectively. The characterization of the reduced and used Ni₁₀CeAl catalyst was performed using BET, H₂-TPR, in-situ XRD, TEM, and TGA-DTG techniques. The in-situ XRD results revealed that Ce₂O₃, CeO₂ and CeAlO₃ coexisted in the Ni₁₀CeAl catalyst after reduction at 850 °C for 2 h. The results of the TEM analysis revealed that the Ni particle size increased after the NGRC reaction, which mainly caused the catalyst deactivation.     

Mixed reforming of methane over Ni–K/CeO2–Al2O3: Study of catalyst performance and reaction kinetics

Syngas can be effectively produced by mixed reforming of methane (MRM). In this work, the performance of Ni–K/CeO₂–Al₂O₃ catalyst in this process was investigated in a fixed-bed reactor in the 923–1073 K range. Both potassium and ceria are renowned for improving the performance of Ni catalyst in the reforming process. The influence of reaction conditions (viz. temperature, space time, feed composition and time-on-stream) on the conversion of two reactants CH₄ and CO₂, yield of the products H₂ and CO and the H₂/CO ratio in syngas were studied. At T = 1073 K and W/Q₀ = 0.17 g-h/L (here, W and Q₀ denote catalyst mass and volumetric flow rate of feed), conversions of CH₄ and CO₂ were 91.2 and 80.1%. When S/C ratio (or steam-to-carbon ratio) in feed increased from 0.2 to 0.5 mol/mol, H₂/CO ratio at T = 1073 K changed from 1.32 to 2.14 mol/mol. The catalyst performed stably for 50 h of time-on-stream. Reaction kinetics was studied between 973 and 1073 K and power law kinetic model was suggested. The apparent activation energy values for consumption of CH₄ and CO₂ were found to be 33.3 and 45.5 kJ/mol, respectively. This work is expected to aid catalyst development and reactor design for the MRM process.     

Optimization of CO2 reforming of methane process for the syngas production over Ni–Ce/TiO2–ZrO2 catalyst using the Taguchi method

In the present study, Taguchi method-based design of experiment with L9 orthogonal array was implemented to optimize the process conditions for CO₂ reforming of methane over the Ni–Ce/TiO₂–ZrO₂ catalyst. The catalyst composition, catalyst reduction temperature, reaction operating temperature, and the CO₂/CH₄ ratio of the reactant gas were the control parameters. The performance index was considered as the response of the Taguchi experiment. The performance index was calculated by considering the product gas H₂/CO ratio, deactivation factor, carbon deposition, and maximum CH₄ conversion. The catalysts were prepared in two steps using the evaporation-induced self-assembly and urea deposition-precipitation methods. The catalysts were characterized in their fresh and spent stages using various techniques like X-ray diffraction, N₂-physisorption, H₂ temperature-programmed reduction, inductively coupled plasma-mass spectroscopy, Scanning electron spectroscopy, Transmission electron spectroscopy, and Thermogravimetric analysis. The results showed that the operating temperature had the principal effect on the performance index. The optimal conditions from signal/noise ratio analysis were Cat3 catalyst with Ti/Zr ratio of 1:3, catalyst reduction temperature of 600 °C, the operating temperature of 800 °C, and feed gas ratio as CO₂/CH₄ = 2. Higher Zr content in the catalyst support and the lower reduction temperature favor enhancing the performance index.     

Highly coke resistant Ni–Co/KCC-1 catalysts for dry reforming of methane

Nanofibrous KCC-1 supported Ni–Co bimetallic catalysts were investigated for dry reforming of methane for syngas generation. Monometallic catalysts such as Ni/KCC-1 and Co/KCC-1, and a series of bimetallic Ni–Co/KCC-1 catalysts were prepared by impregnation and co-impregnation method, respectively. All the catalysts were characterized by XRD, FT-IR, HR-SEM, FE-SEM, XPS, FT-Raman, BET, UV–Visible DRS and AAS techniques. Monometallic nickel supported catalyst contains NiO as an active phase, whereas bimetallic nickel catalysts contain Ni₂O₃, and NiCo₂O₄ on the surface. In the case of cobalt loaded catalysts, spinel Co₃O₄ is the dominant active species, apart from NiCo₂O₄. The addition of cobalt in Ni/KCC-1 has a pronounced effect on the crystallite size, surface area and active species. The hydrogen pretreatment of the catalyst produces bimetallic Ni–Co alloy on the surface. The catalytic activities of the bimetallic catalysts towards dry reforming of methane are better than monometallic catalysts. Mesoporous silica-based KCC-1 offers easy accessibility to the entire surface moieties due to its fibrous nature and the presence of channels, instead of pores. The 2.5%Ni-7.5%Co/KCC-1 showed the maximum CH₄ and CO₂ conversion along with a remarkably low H₂/CO ratio. The life-time test confirms the high thermal stability of the catalysts at 700 °C for 8 h, with less deactivation due to coke formation. The spent catalysts were characterized by XRD, TGA, FT-Raman, and FE-SEM to understand the structural and chemical changes during the reaction. The insignificant D band and G band of graphitic carbon in FT-Raman spectra for the highly active 2.5%Ni-7.5%Co/KCC-1 and 5%Ni–5%Co/KCC-1 catalysts along with TGA results containing 12% weight loss confirms the minimum coke deposition, formation of amorphous carbon and highest coke resistance. The fibrous support restricts the sintering and aggregation of nickel particles as well the deposition of coke. The addition of amphoteric cobalt increases the activity and stability of the catalysts. Ni–Co/KCC-1 with high coke resistance seems to be a promising catalyst for dry reforming of methane.     

Hydrogen production by steam reforming of ethanol over mesoporous Ni–Al2O3–ZrO2 xerogel catalysts: Effect of Zr/Al molar ratio

A series of mesoporous Ni–Al₂O₃–ZrO₂ xerogel catalysts (denoted as Ni-AZ-X) with different Zr/Al molar ratio (X) were prepared by a single-step epoxide-driven sol–gel method, and they were applied to the hydrogen production by steam reforming of ethanol. The effect of Zr/Al molar ratio of Ni-AZ-X catalysts on their physicochemical properties and catalytic activities was investigated. Textural and chemical properties of Ni-AZ-X catalysts were strongly influenced by Zr/Al molar ratio. Surface area of Ni-AZ-X catalysts decreased with increasing Zr/Al molar ratio due to the lattice contraction of ZrO₂ caused by the incorporation of Al³⁺ into ZrO₂. Interaction between nickel oxide species and support (Al₂O₃–ZrO₂) decreased with increasing Zr/Al molar ratio through the formation of NiO–Al₂O₃–ZrO₂ composite structure. Acidity of reduced Ni-AZ-X catalysts decreased with increasing Zr/Al molar ratio due to the loss of acid sites of Al₂O₃ by the addition of ZrO₂. Acidity of Ni-AZ-X catalysts served as a crucial factor determining the catalytic performance in the steam reforming of ethanol; an optimal acidity was required for maximum production of hydrogen. Among the catalysts tested, Ni-AZ-0.2 (Zr/Al = 0.2) catalyst with an intermediate acidity exhibited the best catalytic performance in the steam reforming of ethanol.     

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

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

Thermocatalytic decomposition of methane over mesoporous nanocrystalline promoted Ni/MgO·Al2O3 catalysts

Thermocatalytic decomposition of CH₄ is an interesting method for the production of hydrogen. In this article, the catalytic and structural properties of the La, Ce, Co, Fe, and Cu-promoted Ni/MgO·Al₂O₃ catalysts were investigated in the thermal decomposition of CH₄. Mesoporous MgO·Al₂O₃ powder with the high BET area (>250 m²/g) was synthesized by a novel and simple sol–gel method. The different instrumental methods (XRD, BET, SEM, H₂-TPR and TPO) were used for evaluating the physicochemical characteristics of the samples. The addition of Cu to Ni/MgO·Al₂O₃ dramatically improved the catalytic performance and the Cu-promoted catalysts exhibited the highest CH₄ conversion and H₂ yields among the promoted and unpromoted catalysts. The Cu-promoted catalyst possessed the highest stability in CH₄ conversion during 10 h of reaction. The results also indicated that the Ni–Cu/MgO·Al₂O₃ catalyst with 15 wt.% Cu showed the highest catalytic activity and stability at higher temperatures (>80% CH₄ conversion).     

A comparative study of Ni catalysts supported on Al2O3, MgO–CaO–Al2O3 and La2O3–Al2O3 for the dry reforming of ethane

CO₂ utilization through the activation of ethane, the second largest component of natural and shale gas, to produce syngas, has garnered significant attention in recent years. This work provides a comparative study of Ni catalysts supported on alumina, alumina modified with CaO and MgO, as well as alumina modified with La₂O₃ for the reaction of dry ethane reforming. The calcined, reduced and spent catalysts were characterized employing XRD, N₂ physisorption, H₂-TPR, CO₂-TPD, TEM, XPS and TPO. The modification of the alumina support with alkaline earth oxides (MgO and CaO) and lanthanide oxides (La₂O₃), as promoters, is found to improve the dispersion of Ni, enhance the catalyst's basicity and metal-support interaction, as well as influence the nature of carbon deposition. The Ni catalyst supported on modified alumina with La₂O₃ exhibits a relatively stable syngas yield during 8 h of operation, while H₂ and CO yields decrease substantially for Ni/Al₂O₃.     

Effect of MgO/Al2O3 ratio in the support of mesoporous Ni/MgO–Al2O3 catalysts for CO2 utilization via reverse water gas shift reaction

2 and 5 wt.% nickel was supported on different MgO to Al₂O₃ (M/A) ratios (0.5, 1 and 1.5) and evaluated in reverse water gas shift (RWGS) reaction. The catalysts were prepared by impregnation method and the nanocrystalline supports were synthesized by simple surfactant (CTAB) assisted precipitation technique. The following catalytic activity was observed for 2% & 5% Ni supported on different M/A ratios; M/A = 1 > M/A = 1.5 > M/A = 0.5. The perceived order was related to difference in the structural properties of supports and catalysts. The BET results revealed decrease of specific surface area with increase in M/A ratio, mesoporous structure for M/A = 0.5 and 1 and meso-macroporous structure for M/A = 1.5. The effect of nickel loading on the support with M/A = 1 was also investigated. 1.5% Ni showed high CO₂ conversion of 39.2% at 700 °C and CO selectivity higher than 90% at all temperatures. Increase of nickel loading higher than 1.5% was in favor of CH₄ formation. The TEM images of 1.5% Ni on M/A = 1 revealed uniform distribution of Ni particles with average size of 4.9 nm. The H₂-TPR analysis displayed shifting of maximum temperature of the main peak (γ) to higher temperatures with increase of M/A ratio in the support, indicating harder reducibility of catalysts with higher MgO content. The 1.5% Ni supported on M/A = 1 (MgAl₂O₄) showed great catalytic stability and CO selectivity (>98%) after 15 h on stream.