Preparation and evaluation of Ni/γ-Al2O3 catalysts promoted by alkaline earth metals in glycerol reforming with carbon dioxide

Glycerol is the main by-product in the biodiesel process and can be considered as a promising and renewable source for hydrogen generation through the reforming process. In this work, catalysts with 15 wt% Ni supported on 3 wt% M ? Al₂O₃ (M = MgO, CaO, SrO, and BaO) were prepared and employed in the glycerol dry reforming (GDR) reaction to produce hydrogen and carbon monoxide. The textural characteristics of the fresh and spent catalysts were determined using the ICP, BET, TPR, TPO, and SEM analyses. Based on the obtained results, the catalyst promoted by SrO had the highest catalytic activity. The results indicated that adding various alkaline-earth oxides into the catalyst support decreased the Ni crystalline size from 17.2 nm to 7.4–10.9 nm. Moreover, all promoted catalysts showed better catalytic performance and the promoted sample with 3 wt% SrO possessed higher stability than unpromoted catalyst during 20 h on stream.     

Preparation and characterization of Ni catalysts supported on pillared nanoporous bentonite powders for dry reforming reaction

The Ni/pillared-bentonite catalysts with high BET area were synthesized and used in dry reforming reaction. The effects of different parameters such as calcination temperature, OH⁻/Al³⁺ ratio, temperature and time of pillaring process and the content of nickel on the textural and catalytic properties of the synthesized catalysts were studied. The results indicated that the 15 wt% Ni catalyst supported on pillared bentonite prepared under specified conditions (OH⁻/Al³⁺ = 2.2, pillaring temperature of 40 °C and pillaring time of 3 h) possessed the highest BET area (90.80 m²/g). Also, this catalyst possessed higher catalytic activity and stability with lower amount of deposited carbon in comparison to other prepared catalysts in methane reforming with CO₂.     

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.     

Biogas reforming over bimetallic PdNi catalysts supported on phosphorus-modified alumina

A series of bimetallic PdNi catalysts supported on alumina modified with different amounts of phosphorus (0.5-5 wt%) were prepared. The effect of phosphorus content on the structure, surface properties and catalytic behavior of supported PdNi catalysts in biogas reforming was studied. The physicochemical properties of the samples were characterized by using different techniques: N₂ adsorption-desorption isotherms, X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (TPD), thermogravimetric and differential thermal analysis (TG/DTA) and scanning transmission electron microscopy (STEM). The catalytic properties of the catalysts were evaluated in the reaction of reforming of methane with CO₂. It was shown that increasing the P content (≥1 wt%) leads to agglomeration of the metal Ni particles, as well as to increase of the total acidity of the catalysts. Within bimetallic system, the PdNi catalyst with 0.5 wt% phosphorus showed the best performance and stability caused by the presence of highly dispersed nickel particles on the catalyst surface due to the strong interaction between supported species and alumina.     

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.     

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.     

Ethanol dry reforming over Ni supported on modified ceria-zirconia catalysts– the effect of Ti and Nb dopants

In this work complex metal-oxide catalysts with the general formula 5 wt% Ni/Ce_0·75Zr_0.25-x(Nb,Ti)_xO_2-δ were synthesized by the solvothermal method using supercritical alcohols followed by nickel deposition. The catalysts were characterized and studied in ethanol dry reforming reaction (EDR) in the temperature range 600–750 °C. XRD and TEM showed that the synthesis method provides incorporation of doping cations into the ceria-zirconia fluorite structure, leading to mixed oxides formation. The effect of doping cations on structural and surface properties of 5 wt% Ni/Ce_0·75Zr_0.25-x(Nb,Ti)_xO_2-δ and activity in the EDR reaction was investigated. Oxygen deficiency δ increases with the introduction of titanium and niobium cations, which contributes to the bifunctional reforming mechanism implementation with rapid oxidation of coke precursors and activation of СО₂ at surface oxygen vacancies. TPO-O₂ analysis after reaction showed no carbon formation above 700 °C, and a few carbon deposits (not exceeding 4%) even after significant catalyst deactivation at 600 °C.     

Preparation and improvement of nickel catalyst supported ordered mesoporous spherical silica for thermocatalytic decomposition of methane

The thermocatalytic alteration of CH₄ into highly pure hydrogen and filaments of carbon was investigated on a series of Ni-catalysts with various contents (25, 40, 55, and 70 wt%) supported mesoporous spherical SiO₂. The silica with ordered structure and high specific surface area (1136 m²/g) was synthesized using the Stöber technique with TEOS as a silica precursor and CTAB as the template in a simple synthesis system of aqueous-phase. This technique led to the preparation of mesoporous spherical silica. The prepared samples were characterized using BET, TPR, XRD, TPO, and SEM analyses. The prepared catalysts with different nickel loading showed the BET surface area ranging from 225.0 to 725.7 m²/g. These results indicated that an increase in nickel content decreases the surface area and leads to a subsequent collapse of a pore structure. SEM analysis confirmed a spherical nanostructure of catalysts and revealed that with the increase in loading of Ni, the particle size enlarged, because of the agglomeration of the particles. The results implied that the high methane conversion of 54% obtained over the 55 wt% Ni/SiO₂ at 575 °C and this sample had higher stability at lower reaction temperature than the other prepared catalysts, slowly deactivation was observed for this catalyst at a period of 300 min of time on stream.     

Preparation and improvement of the mesoporous nanostructured nickel catalysts supported on magnesium aluminate for syngas production by glycerol dry reforming

Dry reforming of glycerol is an interesting method for syngas production due to its H₂/CO ≈ 1 that is suitable for FT synthesis. In this study, the performance of the Ni/MgO.Al₂O₃ catalysts with different nickel contents was investigated in glycerol dry reforming. The MgO.Al₂O₃ carrier was prepared by a simple sol-gel method and the nickel-based catalysts were synthesized by the wet impregnation method. The prepared catalysts possessed high BET surface area and pore volume. The TPR analysis showed a strong interaction between Ni and the catalyst support. The results demonstrated that the glycerol conversion decreased by increasing in CO₂/glycerol (GRR) molar ratio. All the prepared samples showed high stability in glycerol dry reforming during 25 h of reaction, indicating the high resistance of the catalysts against carbon formation. Also, 10 wt%Ni/MgO.Al₂O₃ catalysts possessed the highest catalytic performance (52% of glycerol conversion at 750 °C) due to the high dispersion of nickel on the prepared carrier.     

Phosphorus-tuned nickel as high coke-resistant catalyst with high reforming activity

Here we demonstrate that phosphorus (P) can affect both reforming and coking of alumina-supported nickel (10 wt% Ni with respect to alumina) at 750 °C and 1 atm. The P-containing catalysts were prepared by incipient wetness co-impregnation. Compared with the P-free nickel catalyst, the reforming activity is enhanced but the coke content decreases 8-fold at Ni:P atomic ratio of 4; the latter further reduces 55-fold at a ratio of 2, without a substantial decline in the reforming activity. Phosphorus not only improves nickel dispersion but also reduces the surface acidity and facilitates CO₂ activation. At high P loadings, a portion of nickel transforms into nickel oxide during reforming. Besides tuning the reforming and coking activity, phosphorus changes the behavior of carbon crystallization. In methane pyrolysis and dry reforming, filamentous carbon occurs on the P-free catalyst but it is absent on the P-containing catalyst.     

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

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

Promotional effect of Mg in trimetallic nickel-manganese-magnesium nanocrystalline catalysts in CO2 reforming of methane

In the present paper, the dry reforming reaction was studied over the 10 wt%Ni-3wt.%Mn-x wt.% Mg (x = 2, 4 and 6 wt%) catalysts supported on γ-Al₂O₃ with mesoporous structure. The physicochemical characteristics of the samples were determined by XRD, BET, TPO, and SEM techniques. Mesoporous γ-Al₂O₃ carrier with the high BET area (186 m²/g) was synthesized by a simple sol–gel method and the Ni, NiMn and Mg promoted catalysts possessed nanocrystalline mesoporous structure with the BET area in the range of 127–176 m²/g. The average pore radius of the prepared catalysts were smaller than 11 nm. All the synthesized samples exhibited a CH₄ conversion in the range of 60–65% at 700 °C. The small differences in methane conversion in all catalysts could be related to the same nickel loading. According to the TPR results, the Mg addition caused an increase in the reducibility of the nickel catalyst and the Mg-promoted sample exhibited a higher conversion compared to the monometallic catalyst, due to its higher reducibility. The results showed that the textural characteristics of the catalysts were affected by the content of Mg. The results indicated that the NiMn/Al₂O₃ catalyst promoted by 4 wt% Mg showed the highest CH₄ conversion in all studied reaction temperatures (550–700 °C). Furthermore, only one oxidation peak was detected for all catalysts in TPO analysis, which was related to the filamentous form carbon. The 10Ni/Al₂O₃ and 10Ni3Mn4Mg/Al₂O₃ catalysts exhibited the highest and the lowest amount of deposited filamentous carbon, respectively. The 10Ni3Mn4Mg/Al₂O₃ catalyst was stable during the 20 h time on stream without any decline in CH₄ conversion.     

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.     

Hydrogen production via the glycerol steam reforming reaction over nickel supported on alumina and lanthana-alumina catalysts

In the present work, a comparative study of Ni catalysts supported on commercially available alumina and lanthana-alumina carriers was undertaken for the glycerol steam reforming reaction (GSR). The supports and/or catalysts were characterized by PZC, BET, ICP, XRD, NH₃-TPD, CO₂-TPD, TPR and SEM. Carbon deposited on the catalytic surface was characterized by SEM, TPO and Raman. Concerning the Ni/LaAl sample it can be concluded that the presence of lanthana by: (a) facilitating the active species dispersion, (b) strengthening the interactions between nickel species and support, (c) increasing of the basic sites' population and redistributing the acid ones in terms of strength and density, provides a catalyst with improved performance for the GSR reaction, in terms of activity, H₂ production and long term stability. TPO and Raman indicate that the carbon on the Ni/LaAl catalyst was mostly amorphous and was deposited mainly on the support surface. For the Ni/Al catalyst, graphitic carbon was prevalent and likely covered its active sites.     

Syngas production from dry methane reforming over yttrium-promoted nickel-KIT-6 catalysts

Dry reforming of methane was studied over Ni,Y-promoted KIT-6 ordered mesoporous silicas, prepared by incipient impregnation (nickel content 12 wt%, yttrium content of 4 wt%, 8 wt% or 12 wt%). The catalysts were characterized by XRF, FT-IR, TGA/DSC-MS, N₂-adsorption, TEM, HRTEM, XRD and TPR-H₂. The promotion with 8 wt% Y (Y/Si = 0.05) resulted in the highest activity and H₂/CO molar ratio closer to the stoichiometric value at temperatures from 600 to 750 °C. The characterization results of the yttrium promoted materials showed higher reducibility of the bulk NiO, bigger Ni crystallite size after reduction and DRM test, and better dispersion of nickel in the channels of the KIT-6 support. Additionally, larger Ni particles were observed on the external surface of the support, which may be related to catalytic selectivity towards carbon forming reactions. Upon dry methane reforming the segregated phases of Niº, Y₂O₃, and possibly Y₂Si₂O₇ were registered. No presence of a Ni,Y alloy was observed.     

Production of hydrogen by methane dry reforming: A study on the effect of cerium and lanthanum on Ni/MgAl2O4 catalyst performance

Hydrogen production from dry reforming of methane (DRM) was investigated on different Nickel based catalysts deposited on MgAl₂O₄. MgAl₂O₄ spinel was prepared using γ-Alumina supplied from different manufacturers (Sigma Aldrich, Alfa Aesar and Degussa) with low and high specific surface area. Moreover, the influence of different parameters on the catalytic activity on methane dry reforming was studied such as the effect of Ni content, the effect of commercial alumina and the effect of doping nickel with cerium and lanthanum.During this study, the catalytic activity was compared at atmospheric pressure at 750 °C during 4 h then 650 °C during 4 h toward methane dry reforming (DRM) reaction with a molar ratio CH₄/CO₂ = 1/1 and a Weight Hourly Space Velocity (WHSV) of 60.000 mL g⁻¹.h⁻¹. The results showed that among the different catalysts 1.5Ce–Ni5/MgAl₂O₄, synthesized with alumina from Alfa Aesar, exhibited the best catalytic activity for DRM.Furthermore, this catalyst showed the best performance during a stability test at 600 °C for 24 h under reacting mixture with a low carbon formation rate (2.71 mg_C/g_cat/h). Such superior activity is consistent with characterization results from BET, XRD, SEM, TPR and TPO analysis. Furthermore, it seems that the addition of Cerium on Ni/MgAl₂O₄ leads to an increase in catalyst efficiency. It can be due to an effective active oxygen transfer due to the redox properties of CeO_2, leading to the formation of oxygen vacancies offering a benefit for DRM reaction.     

Role of CeO2/ZrO2 mole ratio and nickel loading for steam reforming of n-butanol using Ni–CeO2–ZrO2–SiO2 composite catalysts: A reaction mechanism

This study presents steam reforming of n-butanol to synthesis gas using high surface area mesoporous Ni–CeO₂–ZrO₂–SiO₂ composite catalysts. The reaction proceeds through a combination of dehydrogenation, dehydration, and cracking reactions with propanal, butanal, and C₂–C₄ hydrocarbons as intermediate compounds. The ceria forms a solid solution with zirconia, promotes dispersion of nickel, and enhances oxygen storage/release capacity. The carbon conversion to synthesis gas (CCSG) and hydrogen yield are thus enhanced with increasing CeO₂/ZrO₂ mole ratio up to 1:2 and decreased slightly for higher mole ratios. The CCSG and hydrogen yield are also boosted by increasing the amount of nickel in the catalyst up to 20 wt%. 1:2 CeO₂/ZrO₂ mole ratio and 20 wt% nickel content are thus deliberated as optimum. The optimum catalyst exhibits stable catalytic performance for about 30 h time-on-stream. The study further presents the effect of temperature and steam/carbon mole ratio on n-butanol steam reforming.     

Highly stable and active Ni-mesoporous alumina catalysts for dry reforming of methane

Nanostructured Ni-incorporated mesoporous alumina (MAl) materials with different Ni loading (7, 10 and 15 wt %) were prepared by a template assisted hydrothermal synthesis method and tested as catalysts for CO₂ reforming of methane under different conditions (nickel loading, gas hourly space velocity (GHSV), reaction temperature and time-on-stream (TOS)). The most active catalyst tested (Ni(10 wt%)-MAl) showed a very high stability over 200 h compared to a Ni(10 wt%)/γ-Al₂O₃ prepared using a co-precipitation method which had a significant loss in activity after only ∼4 h of testing. The high stability of the Ni-MAl materials prepared by the template assisted method was due to the Ni nanoparticles in these catalysts being highly stable towards migration/sintering under the reaction conditions used (800 °C, 52,000 mL h⁻¹ g⁻¹). The low susceptibility of the Ni nanoparticles in these catalysts to migration/sintering was most likely due to a strong Ni-support interaction and/or active metal particles being confined to the mesoporous channels of the support. The Ni-MAl catalysts also had significantly lower amounts of carbon deposited compared to the catalyst prepared using the co-precipitation method.     

Ni supported on the CaO modified attapulgite as catalysts for hydrogen production from glycerol steam reforming

The Ni catalyst supported on CaO-modified attapulgite (CaO-ATP) were synthesized by wet impregnation method at a constant Ni metal loading (10 wt%). The catalyst was tested by carrying out a glycerin steam reforming reaction under the following conditions: 400–800 °C, W/G is 3, GHSV is 1 h⁻¹. Ni–CaO-ATP exhibited the highest hydrogen yield (85.30%) and glycerol conversion (93.71%) at 600 °C. The catalysts were characterized by N₂ adsorption/desorption, BET, XRD, H₂-TPR, TG and SEM. The results show that ATP has good resistance to carbon deposition. As an attapulgite modifier of Ni–CaO-ATP, CaO promotes the dispersion of the active component nickel species, which would promote the water gas shift reaction, leading to the improving of hydrogen yield. In addition, the addition of Ca would further enhance the inhibition of carbon deposition and prolong the life of the Ni–CaO-ATP catalyst.     

Ni supported on MgO modified attapulgite as catalysts for hydrogen production from glycerol steam reforming

A series of Mg-modified Ni/Attapulgite (ATP) catalysts have been prepared by impregnation method for glycerol steam reforming to produce hydrogen. The physicochemical properties of catalysts were characterized using various techniques including N₂ physical adsorption analysis, XRD, H₂-TPR, SEM, TEM and NH₃-TPD. The results of N₂ physical adsorption indicated MgO modified Ni-based catalysts had unique mesostructure, resulting in the high metal dispersion and interaction between active metal and support as proven by XRD, TEM and H₂-TPR. Results of glycerin reforming experiments showed that Ni/10MgO/ATP catalyst had the highest activity than that of the other catalysts. Ni/10MgO/ATP catalyst had the smallest Ni average crystal size (10.1 nm) and the highest surface area (110.31 m²/g). These excellent properties made it show the enhanced glycerol conversion (94.71%) and a higher H₂ yield (88.45%) and the longest stability (30 h) during glycerol steam reforming (GSR) at 600 °C, W/G = 3, and WHSV = 1 h^?1. The used catalysts after 60 h of glycerin reforming experiments were also investigated by XRD, SEM, TEM, Roman and TG-DTG. The results indicated that the addition of Mg significantly inhibited the sintering of nickel grains and the formation of amorphous carbon. Therefore, Ni/10MgO/ATP catalyst increased the activity of the catalyst and extended the life of the catalyst.