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.     

Promotional effect of Ru on the activity and stability of Co/SBA-15 catalysts in dry reforming of methane

The catalysts in this study were prepared via the “two-solvents” impregnation method and labeled as: xCo and yRu-xCo/SBA-15 (x = 12 wt%, y = 0.75–1.125–1.5 wt%). These catalysts were characterized by N₂ sorption, X-Ray Diffraction (XRD) techniques, Transmission Electron Microscopy (TEM) analyses and Temperature Programmed Oxidation/Reduction (TPO/TPR). The catalytic activity of mono (Co) and bimetallic (Co–Ru) supported on SBA-15 was investigated in the dry reforming of methane (DRM) reaction.     

Catalytic performance of Samaria-promoted Ni and Co/SBA-15 catalysts for dry reforming of methane

Methane reforming with CO₂ over Samaria-promoted Ni and Co/SBA-15 was comparatively investigated. The Co, Ni (10%wt) and Sm (0.5, 1 and 1.5%wt) ions were introduced by two-solvent impregnation method. The Ni and Co catalysts with/without promoter, were examined by N2 adsorption-desorption, x-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), temperature programmed reduction (TPR) and thermogravimetric analysis (TGA) methods, and then evaluated in CO₂ reforming of methane. The XRD and TEM results indicated that Ni and Co/SBA-15 promoted by 1%wt of Samaria, had the smallest NiO and Co₃O₄ particles size and the highest dispersion; as a result, they would rather studying dry reforming of methane test. Catalytic results indicated that Samaria promoted Ni/SBA-15 had the highest conversion (CH₄ conversion～58% at 700 °C), while a remarkable decrease of catalytic activity was observed over Samaria-promoted Co/SBA-15 (CH₄ conversion～25% at 700 °C). The positive effect of Samaria on Ni/SBA-15 catalyst activity is probably due to smaller NiO particles, higher NiO dispersion and lower trend to carbon deposition. On the contrary, the negative effect of Samaria on Co/SBA-15 catalyst activity is maybe due to Co oxidation to inactive phase and sintering of Co particles in high temperatures.     

Physico-chemical properties and syngas production via dry reforming of methane over NiAl2O4 catalyst

Nano-particles of NiAl₂O₄ were prepared by co-precipitation and their bulk and surface were characterized by XRD, Raman spectroscopy, N₂-adsorption-desorption analysis, SEM-EDS and XPS. The reducibility was studied by TPR and HTXRD techniques under H₂ atmosphere. The synthetized catalyst was made of NiAl₂O₄ spinel oxide as main phase and of NiO (10%) free oxide. Interestingly, it was shown that the surface was richer in Al species. The catalytic performances in methane dry reforming were evaluated without H₂-pretreatment of catalyst. A very high activity was observed with conversion of methane and CO₂ at 750 °C of 84 and 90 mol%, respectively and high H₂/CO ratio. The amount of coke deposited during the reaction on this spinel was ～3.6%. The physico-chemical properties of the catalyst on their behavior in the dry reforming of methane are discussed.     

Ce promoting effect on the activity and coke formation of Ni catalysts supported on mesoporous nanocrystalline γ-Al2O3 in autothermal reforming of methane

In this study methane autothermal reforming (ATR) was investigated over Ni/Al₂O₃ and Ni/Al₂O₃–CeO₂ catalysts. The catalyst carriers were prepared through a facile one-step method, which produced mesoporous nanocrystalline carriers for Ni catalysts. The samples were characterized by XRD, TPR, BET, TPO and SEM characterization techniques and the catalytic activity and stability were also studied at different conditions (GHSV and feed ratio) in methane ATR. It was found that the nickel catalyst supported on 3 wt.% Ce–Al₂O₃ exhibited higher activity compared to the catalysts supported on the Al₂O₃ and promoted Al₂O₃ with 1 and 6 wt.% Ce. The results also showed that the nickel catalyst supported on 3 wt.% Ce–Al₂O₃ possessed the highest resistance against carbon deposition in ATR reaction.     

Preparation of nanocrystalline Zr,La and Mg-promoted 10% Ni/Ce0.95Mn0.05O2 catalysts for syngas production via dry reforming reaction

The influence of the various promoters (Zr, La and Mg) on the physicochemical and catalytic characteristics of the 10% Ni/Ce_0.95Mn_0.05O₂ solid solution catalyst were investigated in methane dry reforming at atmospheric pressure. The co-precipitation method was employed for the synthesis of the catalyst carrier. The catalysts were characterized by BET, XRD, H₂-TPR and TPO analyses. The obtained results revealed that the addition of the promoters increased the BET surface area and the highest BET surface area was related to the catalyst promoted by La (58.99 m²/gr). The results of the TPR analysis showed that the broad peak related to the reduction of NiO species was shifted to the higher temperature, indicating the enhancement of the interaction between NiO particles and the support due to the addition of the promoter. The obtained results indicated that the addition of Mg improved the activity (CH₄ conversion (%) = 67 at 700 °C) and stability and reduced the amount of deposited carbon. Furthermore smaller Ni crystalline size was related to the catalyst promoted by Mg (10.0 nm). The highest and the lowest amount of carbon deposition was observed on the 10Ni/Ce_0.95Mn₀.₀₅O₂ and 10Ni/Ce_0.85Zr_0.10Mn_0.05O₂ catalysts, respectively.     

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.     

Mo-promoted Ni/Al2O3 catalyst for dry reforming of methane

Mo-promoted alumina supported Ni catalysts were prepared through a conventional impregnation method and tested in dry reforming of methane (DRM) at temperatures from 550 to 850 °C. The catalysts were characterized by means of H₂-temperature programmed reduction (H₂-TPR), CO₂-temperature programmed desorption (CO₂-TPD), X-ray diffraction (XRD), N₂ physisorption and Raman spectroscopy. Mo-promotion caused a reduction in the DRM catalytic activity. The weaker interaction between NiO species and the alumina support, the formation of a MoNi₄ phase, and the lower basicity of this Ni-Mo/Al₂O₃ catalyst were identified as the main causes for its lower activity. However, pre-reducing the Ni-Mo/Al₂O₃ catalyst at temperatures lower than 700 °C, instead of 900 °C, resulted in a considerable increase of its catalytic activity. This was mainly due to the formation of a separate Ni⁰ phase that did not interact with Mo and to an increase in medium strength basicity.     

Mesoporous nanostructured Ni/MgAl2O4 catalysts: Highly active and stable catalysts for syngas production in combined dry reforming and partial oxidation

In this paper, the combination of dry reforming and partial oxidation of methane on nickel catalysts supported on mesoporous MgAl₂O₄ was investigated. The support was prepared by a facile sol-gel route using propylene oxide as a gelation agent. The characterizations of the catalysts were performed by BET, XRD, TPR, TPO, TPH, UV–vis, CO-dispersion, SEM and TEM techniques. In addition, the effects of nickel content, reaction and reduction temperatures, feed ratio and the GHSV value on the physicochemical and catalytic properties were studied. The results revealed that the nickel content had an optimum value of 7.5 wt% and the catalyst with this content of nickel exhibited the highest activity. Furthermore, the results demonstrated that the increase in reaction temperature enhanced the rate of the dry reforming reaction and led to obtain a H₂/CO ratio around unity. The 7.5 wt% nickel catalyst showed a 5% decline in activity within 15 h in combined reforming. The TPO analysis showed that there was no deposited carbon on the catalyst surface in combined reforming and the SEM analysis confirmed the results of TPO analysis.     

Hydrogen and syngas production by methane dry reforming on SBA-15 supported nickel catalysts: On the effect of promotion by Ce0.75Zr0.25O2 mixed oxide

In this work, the effects of doping Ni-based SBA-15 catalysts with Ceria–Zirconia mixed oxide (CZ) on the activity and stability of these catalysts during syngas production by methane dry reforming (MDR) were investigated and compared with the activity and stability of unmodified Ni/SBA-15. The above catalysts were prepared by incipient wetness impregnation (IWI) with different impregnation strategy. The samples were characterized by nitrogen physisorption, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), temperature programmed reduction (TPR) and H₂ chemisorption. The results indicated that the unmodified Ni/SBA-15 showed clear deactivation especially in the first period of the stability test and between 600 °C and 630 °C during the activity test whereas the CZ modified samples had better stability.     

A comparative study of dry reforming of methane over nickel catalysts supported on perovskite-type LaAlO3 and commercial α-Al2O3

A systematic and comparative study was made to determine the influence of perovskite-type LaAlO₃ and commercial α-Al₂O₃ on the performance of nickel-based catalysts in dry reforming of methane (DRM). The perovskite-type LaAlO₃ was selected due to its characteristics of solid state semiconductor with oxygen vacancies and high structural stability. The catalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), N₂ adsorption-desorption, temperature programmed reduction (TPR-H₂), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The catalyst performance was evaluated based on activity tests (600–800 °C) and short- and long-term stability (10 and 20 h) at 700 °C at a GHSV (Gas Hourly Space Velocity) of 18 and 72 L g^?1 h^?1. The TPR-H₂ profiles indicate that the oxygen vacancies on the perovskite surface exerted a strong effect on the reduction temperature and reducibility of the NiO nanoparticles, resulting in weak Ni⁰/support interaction. The results of the tests after 10 h under GHSV of 18 L g^?1 h^?1 indicate that the Ni/LaAlO₃ catalyst is 7.8 and 11.5% more stable than Ni/α-Al₂O₃ in the conversions of CH₄ and CO₂, respectively. The higher stability and activity of Ni/LaAlO₃ is directly ascribed to the presence of NiO (3.38 wt%) after activation, which promoted the formation of carbon nanotubes (CNT) and increased the dispersion of the metallic phase. Even under severe conditions of activation and reaction (high GHSV), as in the long-term test, the Ni/LaAlO₃ catalyst showed a 37.2% higher H₂ yield than the Ni/α-Al₂O₃. Analyses by TEM indicate that the Ni/α-Al₂O₃ catalyst exhibited deactivation problems associated with sintering effects. Thus, the presence of structural defects and surfaces rich in oxygen vacancies makes LaAlO₃ perovskite a potential support for application in methane catalytic reforming processes.     

Hydrogen production from partial oxidation of methane over dielectric barrier discharge plasma and NiO/γ-Al2O3 catalyst

Hydrogen production from partial oxidation of methane under the combination of dielectric barrier discharge (DBD) plasma and NiO/γ-Al₂O₃ catalyst with cordierite honeycomb monoliths as substrate was investigated. The results showed that obvious synergistic effect was generated between DBD plasma and catalyst. Compared with the DBD plasma reactor without catalyst, the CH₄ conversion and H₂ yield increased from 60.1% and 21.3% to 83.6% and 28.4%, respectively. When the discharge power is above 70 W, the combination of DBD plasma and NiO/γ-Al₂O₃ catalyst promotes partial oxidation of methane. The catalyst was characterized by X-ray diffraction (XRD). NiO on the surface of catalyst was reduced to Ni because of the introduction of DBD plasma. The activity of catalyst at low temperature was improved, and the generation of oiliness by-products was significantly reduced.     

Bi-reforming of methane on Ni/SBA-15 catalyst for syngas production: Influence of feed composition

Bi-reforming of methane (BRM) was evaluated for Ni catalyst dispersed on SBA-15 support prepared by hydrothermal technique. BRM reactions were conducted under atmospheric condition with varying reactant partial pressure in the range of 10–45 kPa and 1073 K in fixed-bed reactor. The ordered hexagonal mesoporous SBA-15 support possessing large specific surface area of 669.5 m² g^?1 was well preserved with NiO addition during incipient wetness impregnation. Additionally, NiO species with mean crystallite dimension of 14.5 nm were randomly distributed over SBA-15 support surface and inside its mesoporous channels. Thus, these particles were reduced at various temperatures depending on different degrees of metal-support interaction. At stoichiometric condition and 1073 K, CH₄ and CO₂ conversions were about 61.6% and 58.9%, respectively whilst H₂/CO ratio of 2.14 slightly superior to theoretical value for BRM would suggest the predominance of methane steam reforming. H₂ and CO yields were significantly enhanced with increasing CO₂/(CH₄ + H₂O) ratio due to growing CO₂ gasification rate of partially dehydrogenated species from CH₄ decomposition. Additionally, a considerable decline of H₂ to CO ratio from 2.14 to 1.83 was detected with reducing H₂O/(CH₄ + CO₂) ratio due to dominant reverse water-gas shift side reaction at H₂O-deficient feedstock. Interestingly, 10%Ni/SBA-15 catalyst was resistant to graphitic carbon formation in the co-occurrence of H₂O and CO₂ oxidizing agents and the mesoporous catalyst structure was still maintained after BRM. A strong correlation between formation of carbonaceous species and catalytic activity was observed.     

Effect of substitution by Ni in MgAl2O4 spinel for biogas dry reforming

Mesoporous nanocrystalline Mg_1-xNi_xAl₂O₄ (x = 0.10, 0.13, 0.17 and 0.20) with large surface area were synthesized via a simple one-step sol-gel method using nonprecious metals. The prepared Mg_1-xNi_xAl₂O₄ catalysts exhibit good catalytic performance towards methane and carbon dioxide dry reforming reaction. The catalysts were evaluated by various techniques, including XRD, BET, TPR, TPO, EPR, Chemisorption, SEM and TEM. All the Ni incorporated MgAl₂O₄ samples possessed high BET area (296–305 m² g^?1) and pore volume (0.47–0.56 cm³ g^?1) with small pore size (6.4–7.4 nm) in meso region after calcination at 700 °C. The TPR results suggested strong interaction effect in NiMg and the reducibility property of the catalysts improved with the increase of nickel doping. Mg_0.8Ni_0.2Al₂O₄ exhibited the highest activity for biogas dry reforming with 72.6% CH₄ and 80.7% CO₂ conversion at 700 °C. Electron paramagnetic resonance (EPR) results indicated that the incorporation of Ni in MgAl₂O₄ spinel lattice led to the lattice distortion and formed oxygen vacancies which are a benefit for the dry reforming reaction.     

Hydrogen production by steam reforming of model bio-oil using structured Ni/Al2O3 catalysts

This study focuses on hydrogen production from the steam reforming of model bio-oil over Ni/Al₂O₃ catalysts prepared in two different geometries (monolith and pellet) using the dip-coating and wet impregnation methods and characterized using Powder X-Ray diffraction, Temperature Programmed Reduction, Scanning Electron Microscopy (SEM) and BET Surface area analysis. The effects of the catalyst geometry and reforming temperatures were studied by carrying out experiments at the optimal conditions of T = (823, 923, 1023) K and S/C ratio = 13 determined from the thermodynamic analysis of the process prior to the experiments using the process simulator PRO-II. The experimental results showed high steady state H₂ yield corresponding to 2.58 and 1.73 mol (out of 5.13 mol) using monolithic and the pelletized catalysts respectively. The product distribution achieved with the monolithic catalyst was closer to the thermodynamic results suggesting a higher selectivity to hydrogen production.     

Non-oxidative decomposition of methane/methanol mixture over mesoporous Ni-Cu/Al2O3 Co-doped catalysts

Thermocatalytic decomposition of methane (TCD) is reported to be a promising and green route of hydrogen generation, however, the relatively fast catalyst deactivation is the main drawback of this technology. This article reports an attempt to increase the catalyst deactivation time by using Cu promoted Ni-based catalyst, and methanol premixed methane gas as a feedstock. The catalysts were prepared by wet impregnation method and characterized by TGA, BET, XRD, TPR, FESEM, Raman and TEM. An inevitable decline in surface area from 5.15 to 4.52 m²g^-1 due to the addition of 15%Cu on 50%Ni/Al₂O₃ was due to the agglomeration of particles and pore blockage of γ -Al₂O₃ support. Moreover, the reduction of NiO was shifted towards lower temperature by successful impregnation of Cu promoter. The overlapping peaks of NiO and CuO confirmed the formation of mixed oxides Ni_x Cu _(1-x) O via XRD analysis. The catalytic activity of both catalysts showed that 50%Ni-15%Cu/Al₂O₃ resulted in better methane conversion 75% at 1023 K TOS for 6 h. The post reaction analysis of the catalysts revealed that carbon in the form of CNF got deposited on the surface of the catalyst having amorphous and crystalline morphology. Finally, TEM also revealed that GF, CNF, and MWCNF were encapsulated over the surface of 50%Ni-15%Cu/Al₂O_3.     

Promotional effects of Ce on NiCe/γAl2O3 for enhancement of H2 in hydrothermal gasification of biomass

This communication presents promotional effects of Ce on a NiCe/γ-Al₂O₃ catalyst for biomass gasification in hydrothermal reaction conditions. The catalyst samples were prepared by an incipient wetness technique using a successive metal loading approach. The TPR/TPO results showed that the presence of Ce minimized metal support interaction and improved the reducibility and thermal stability of the catalyst. The XRD analysis of fresh and reduced (after 10 repeated TPR/TPO cycles) catalyst samples showed unchanged crystal structures of the nickel particles indicating stable properties of the NiCe/γAl₂O₃ catalyst. The hydrothermal biomass gasification experiments were conducted using glucose as a biomass surrogate at various reaction temperature (425–525 °C) and time (5–35 min), while the pressure was maintained at 25.5 MPa. It was observed that the addition of Ce influenced the catalyst surface creating more active nickel sites for steam reforming methane reaction. Ce also increased the activity of Ni/γAl₂O₃ catalysts in terms of hydrogen production by promoting the water gas shift reaction and suppressing the methanation reaction of carbon dioxide.     

Catalytic steam reforming of glycerol over Ni–La2O3–CeO2/SBA-15 catalyst for stable hydrogen-rich gas production

Ni-based catalysts (Ni, Ni–La₂O₃, and Ni–La₂O₃–CeO₂) on mesoporous silica supports (SBA-15 and KIT-6) were prepared by an incipient wetness impregnation and tested in glycerol steam reforming (GSR) for hydrogen-rich gas production. The catalysts were characterized by the N₂-physisorption, TPD, X-ray diffraction (XRD), SEM-EDS, and TEM techniques. N₂-physisorption results of calcined catalysts highlight that adding of La₂O₃ increased surface area of the catalyst by preventing pore mouth plugging in SBA-15, which was frequently observed due to the growth of NiO crystals. A set of GSR experiments over the catalysts were performed in an up-flow continuous packed-bed reactor at 650 °C and atmospheric pressure. The highest hydrogen concentration of 62 mol% was observed with a 10%Ni–5%La₂O₃ –5%CeO₂/SBA-15 catalyst at a LHSV of 5.8 h⁻¹. Adding of CeO₂ to the catalyst appeared to increase catalytic stability by facilitating the oxidative gasification of carbon formed on/near nickel active sites of Ni–La₂O₃–CeO₂/SBA-15 and Ni–La₂O₃–CeO₂/KIT-6 catalyst during the glycerol steam reforming reaction.     

Preparation of nickel catalysts supported on CaO.2Al2O3 for methane reforming with carbon dioxide

Nanocrystalline calcium aluminate (CaO.2Al₂O₃) was prepared by a simple co-precipitation method using Poly (ethylene glycol)-block-poly(propylene glycol)-block poly(ethylene glycol) (PEG-PPG-PEG, MW:5800) as surfactant and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by X-ray diffraction (XRD), N₂ adsorption (BET), Temperature programmed reduction and oxidation (TPR-TPO) and Scanning electron microscopy (SEM) techniques. The results showed that the prepared support has a high potential as support for nickel catalysts in methane reforming with carbon dioxide. The results showed high catalytic activity and stability for the prepared catalysts. Among the prepared catalysts 15% Ni/CaO.2Al₂O₃ was the most active catalyst and showed the highest affinity for carbon formation. In addition, 7% Ni/CaO.2Al₂O₃ possessed high catalytic stability during 50 h time on stream. The TPO analysis revealed that increasing in nickel content increased the amount of deposited carbon over the spent catalysts. SEM results detected only whisker type of carbon for all spent catalysts.     

CO2 reforming of methane over Ni/SBA-15 prepared with β-cyclodextrin – Role of β-cyclodextrin in Ni dispersion and performance

Ni/SBA-15-CD(1/X) catalysts were prepared by the impregnation of a certain amount of Ni(NO₃)₂ and various contents of β-cyclodextrin (CD), in which 1/X indicates the molar ratio of CD to Ni. The physicochemical properties of the catalysts were characterized by BET, XRD, TEM, TPR and TGA, and their catalytic performance in the CO₂ reforming of methane to syngas was evaluated using a fixed-bed quartz reactor. The characterization results revealed that Ni/SBA-15-CD(1/X) prepared with n(CD)/n(Ni) ratios in the range of 1/66–1/33 possessed smaller NiO particles and exhibited stronger interactions between NiO and SBA-15, whereas NiO particles were not well-dispersed on Ni/SBA-15-CD(1/X) catalysts prepared with further CD addition (1/X = 1/8 and 1/1). The reaction results indicated that the better-dispersed Ni/SBA-15-CD(1/X) catalysts, such as Ni/SBA-15-CD(1/66), Ni/SBA-15-CD(1/50) and Ni/SBA-15-CD(1/33), exhibited higher conversions and stronger abilities to resist carbon deposition. Regarding the role of CD in dispersing Ni particles, it could be speculated that complexes were formed between CD and Ni²⁺, as well as NO₃⁻, which would change the state of Ni species during the impregnation and heat treatment processes.