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.     

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.     

Syngas production from glycerol-dry(CO2) reforming over La-promoted Ni/Al2O3 catalyst

A 3 wt% La-promoted Ni/Al₂O₃ catalyst was prepared via wet co-impregnation technique and physicochemically-characterized. Lanthanum was responsible for better metal dispersion; hence higher BET specific surface area (96.0 m² g⁻¹) as compared to the unpromoted Ni/Al₂O₃ catalyst (85.0 m² g⁻¹). In addition, the La-promoted catalyst possessed finer crystallite size (9.1 nm) whilst the unpromoted catalyst measured 12.8 nm. Subsequently, glycerol dry reforming was performed at atmospheric pressure and temperatures ranging from 923 to 1123 K employing CO₂-to-glycerol ratio from zero to five. Significantly, the reaction results have yielded syngas as main gaseous products with H₂:CO ratios always below than 2.0 with concomitant maximum 96% glycerol conversion obtained at the CO₂-to-glycerol ratio of 1.67. In addition, the glycerol consumption rate can be adequately captured using power law modelling with the order of reactions equal 0.72 and 0.14 with respect to glycerol and CO₂ whilst the activation energy was 35.0 kJ mol⁻¹. A 72 h longevity run moreover revealed that the catalyst gave a stable catalytic performance.     

LDH-derived Ni–MgO–Al2O3 catalysts for hydrogen-rich syngas production via steam reforming of biomass tar model: Effect of catalyst synthesis methods

Steam reforming of toluene (SRT) as a model tar compound is studied on Ni–MgO–Al₂O₃ hydrotalcite synthesized by different methods: urea hydrolysis, coprecipitation, and wet impregnation. The two wet-impregnated catalysts were produced by immersing MgO–Al₂O₃ hydrotalcites synthesized by urea hydrolysis and coprecipitation in Ni²⁺ solution to produce the corresponding impregnated catalysts. Among all the catalysts, both the samples prepared by urea hydrolysis gave superior toluene conversion of ~85% and also improved the resistance to carbon deposits. The two coprecipitation catalysts had a low toluene conversion of ~63% and also produced more coke. The X-ray photoelectron spectroscopy studies showed that impregnated catalyst produced from urea hydrolysis imparted greater metal-support interaction; whereas the coprecipitation impregnation catalysts only weakly interacted with the support. The CO₂ temperature programmed desorption measurement of the reduced catalysts showed that urea hydrolysis catalysts possessed higher surface basicity as compared to coprecipitation catalysts. This high basic character aided in suppressing the coke formation. HRTEM results also revealed that urea hydrolysis produced smaller Ni⁰ particles (6–7 nm) and coprecipitation produced larger particles (10–20 nm). The excellent reforming properties of urea hydrolysis is due to smaller Ni⁰ particle size and greater surface basicity which aided in improving the catalytic performance and suppressing coke.     

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.     

Unravelling the synergistic promotion effect of simultaneous doping Fe and Cr into Cu-based spinel oxide on methanol steam reforming

The effects of Fe and Cr species on Cu-based supported and spinel oxide catalysts during methanol steam reforming (MSR) reaction and the Cu–Fe–Cr synergy were investigated. Herein, a series of Al₂O₃ supported catalysts were prepared. And their MSR performance was evaluated. The addition of Fe and Cr had a significant promotion on MSR performance compared with the corresponding Cu-based catalyst. In order to unravel the beneficial effect, CuFe, CuCr, CuAl, CuFeAl, CuCrAl and CuFeCr catalysts were synthesized by the hydrothermal method. And BET, XRD, SEM-EDX mapping, HRTEM, H₂-TPR, NH₃-TPD, CH₃OH-TPD and XPS characterizations were performed. Results showed that CuFeCr catalyst possessed superior MSR behaviors. At the temperature of 260–270 °C, its methanol conversion was maintained above 80% during a time-on-stream stability of 100 h. And it exhibited better fast start-up behaviors than commercial catalyst. In combination with the characterizations, it was assumed that the excellent catalytic performance of the CuFeCr catalyst was attributed to its moderate Cu⁺ content and O_vac/O_ads ratio. And it was the result of the Cu–Fe–Cr synergistic effect.     

Hydrogen production from glycerol dry reforming over Ag-promoted Ni/Al2O3

In recent times, glycerol has been employed as feedstock for the production of syngas (H₂ and CO) with H₂ as its main constituent. This study centers on dry reforming of glycerol over Ag-promoted Ni/Al₂O₃ catalysts. Prior to characterization, the catalysts were synthesized using the wet impregnation method. The reforming process was carried out using a fixed bed reactor at reactor operating conditions; 873–1173 K, carbon dioxide to glycerol ratio of 0.5 and gas hourly space velocity (WHSV) in the range of 14.4 ≤ 72 L g_cat⁻¹ h⁻¹). Ag (3)-Ni/Al₂O₃ gave highest glycerol conversion and hydrogen yield of 40.7% and 32%, respectively. The optimum conditions which gave highest H₂ production, minimized methane production and carbon deposition were reaction temperature of 1073 K and carbon dioxide to glycerol ratio of 1:1. This result can attributed to the small metal crystallite size characteristics possessed by Ag (3)–Ni/Al₂O₃, which enhanced metal dispersion in the catalyst matrix. Characterization of the spent catalyst revealed the formation of two types of carbon species; encapsulating and filamentous carbon which can be oxidized by O₂.     

A highly active and stable chromium free iron based catalyst for H2 purification in high temperature water gas shift reaction

In this work mesoporous nanocrystalline chromium free Fe–Al–Ni catalysts with various Fe/Al and Fe/Ni ratios were prepared by coprecipitation method for high temperature water gas shift reaction. The prepared catalysts were characterized using X-ray diffraction (XRD), N₂ adsorption (BET), temperature-programmed reduction (TPR) and transmission electron microscopy (TEM) techniques. The catalytic results revealed that the catalyst with Fe/Al = 10 and Fe/Ni = 5 weight ratios exhibited the highest catalytic activity among the prepared catalysts and the commercial chromium containing one. This catalyst possessed a high surface area of 177.4 m² g⁻¹ with an average pore size of 4.3 nm with a high stability during 20 h time on stream. Furthermore, the effect of calcination temperature, GHSV and steam/gas ratio on the structural properties and catalytic performance of the catalyst with the highest activity was investigated.     

Production of CO-rich hydrogen gas from glycerol dry reforming over La-promoted Ni/Al2O3 catalyst

Dry reforming of glycerol has been carried out over alumina-supported Ni catalyst promoted with lanthanum. The catalysts were characterized using EDX, liquid N₂ adsorption, XRD technique as well as temperature-programmed reduction. Significantly, catalytic glycerol dry reforming under atmospheric pressure and at reaction temperature of 1023 K employing 3 wt%La–Ni/Al₂O₃ catalyst yielded H₂, CO and CH₄ as main gaseous products with H₂:CO < 2.0. Post-reaction, XRD analysis of used catalysts showed carbon deposition during glycerol dry reforming. Consequently, BET surface area measurement for used catalysts yielded 10–21% area reduction. Temperature-programmed gasification studies with O₂ as a gasification agent has revealed that La promotion managed to reduce carbon laydown (up to 20% improvement). In comparison, the unpromoted Ni/Al₂O₃ catalyst exhibited the highest carbon deposition (circa 33.0 wt%).     

Catalytic characteristics of innovative Ni/slag catalysts for syngas production and tar removal from biomass pyrolysis

In this study, innovative Ni-based catalysts supported by five typical slag carriers (magnesium slag (MS), steel slag (SS), blast furnace slag (BFS), pyrite cinder (PyC) and calcium silicate slag (CSS)) were prepared by wet impregnation. With the prepared catalysts and Ni/γ-Al₂O₃ catalyst, catalytic reforming of pyrolysis volatiles from pine sawdust for syngas production and tar removal was investigated. The catalysts were characterized by BET, XRD, SEM, TEM and Raman. The catalytic performances of the six catalysts were decreasing in the following order: Ni/MS > Ni/γ-Al₂O₃ > Ni/SS > Ni/BFS > Ni/CSS > Ni/PyC. Ni/MS catalyst exhibited excellent catalytic reactivity as well as thermal stability in terms of tar conversion (95.19%), gas yield (1.46 Nm³/kg) and CO₂ capture ability (CO₂ yield of 0.5%). Both amorphous carbon and graphite-type carbon were formed on the catalysts after catalytic reforming and the D/G ratio (the relative intensity ratio of the D-band to the G-band) was positively correlated to the catalytic activity.     

Characterization and activity test of commercial Ni/Al2O3, Cu/ZnO/Al2O3 and prepared Ni–Cu/Al2O3 catalysts for hydrogen production from methane and methanol fuels

In this study, methane and methanol steam reforming reactions over commercial Ni/Al₂O₃, commercial Cu/ZnO/Al₂O₃ and prepared Ni–Cu/Al₂O₃ catalysts were investigated. Methane and methanol steam reforming reactions catalysts were characterized using various techniques. The results of characterization showed that Cu particles increase the active particle size of Ni (19.3 nm) in Ni–Cu/Al₂O₃ catalyst with respect to the commercial Ni/Al₂O₃ (17.9). On the other hand, Ni improves Cu dispersion in the same catalyst (1.74%) in comparison with commercial Cu/ZnO/Al₂O₃ (0.21%). A comprehensive comparison between these two fuels is established in terms of reaction conditions, fuel conversion, H₂ selectivity, CO₂ and CO selectivity. The prepared catalyst showed low selectivity for CO in both fuels and it was more selective to H₂, with H₂ selectivities of 99% in methane and 89% in methanol reforming reactions. A significant objective is to develop catalysts which can operate at lower temperatures and resist deactivation. Methanol steam reforming is carried out at a much lower temperature than methane steam reforming in prepared and commercial catalyst (275–325 °C). However, methane steam reforming can be carried out at a relatively low temperature on Ni–Cu catalyst (600–650 °C) and at higher temperature in commercial methane reforming catalyst (700–800 °C). Commercial Ni/Al₂O₃ catalyst resulted in high coke formation (28.3% loss in mass) compared to prepared Ni–Cu/Al₂O₃ (8.9%) and commercial Cu/ZnO/Al₂O₃ catalysts (3.5%).     

Preparation of Ni–Cu/Mg/Al catalysts from hydrotalcite-like compounds for hydrogen production by steam reforming of biomass tar

Ni–Cu/Mg/Al bimetallic catalysts were prepared by the calcination and reduction of hydrotalcite-like compounds containing Ni²⁺, Cu²⁺, Mg²⁺, and Al³⁺, and tested for the steam reforming of tar derived from the pyrolysis of biomass at low temperature. The characterizations with XRD, STEM-EDX, and H₂ chemisorption confirmed the formation of Ni–Cu alloy particles. The Ni–Cu/Mg/Al bimetallic catalyst with the optimum composition of Cu/Ni = 0.25 exhibited much higher catalytic performance than the corresponding monometallic Ni/Mg/Al and Cu/Mg/Al catalysts in the steam reforming of tar in terms of activity and coke resistance. The catalyst gave almost total conversion of tar even at temperature as low as 823 K. This high performance was related to the higher metal dispersion, larger amount of surface active sites, higher oxygen affinity, and surface modification caused by the formation of small Ni–Cu alloy particles. In addition, the Ni–Cu/Mg/Al catalyst showed better long-term stability than the Ni/Mg/Al catalyst. No obvious aggregation and structural change of the Ni–Cu alloy particles were observed. The coke deposition on the Ni–Cu/Mg/Al catalyst was approximately ten times smaller than that on the Ni/Mg/Al catalyst, indicating good coke-resistance of the Ni–Cu alloy particles.     

Ni/Ru–Mn/Al2O3 catalysts for steam reforming of toluene as model biomass tar

The catalytic steam reforming of the major biomass tar component, toluene, was studied over two commercial Ni-based catalysts and two prepared Ru–Mn-promoted Ni-base catalysts, in the temperatures range 673–1073 K. Generally, the conversion of toluene and the H₂ content in the product gas increased with temperature. A H₂-rich gas was generated by the steam reforming of toluene, and the CO and CO₂ contents in the product gas were reduced by the reverse Boudouard reaction. A naphtha-reforming catalyst (46-5Q) exhibited better performance in the steam reforming of toluene at temperatures over 873 K than a methane-reforming catalyst (Reformax 330). Ni/Ru–Mn/Al₂O₃ catalysts showed high toluene reforming performance at temperatures over 873 K. The results indicate that the observed high stability and coking resistance may be attributed to the promotional effects of Mn on the Ni/Ru–Mn/Al₂O₃ catalyst.     

Effect of CaO addition on acid properties of Ni–Ca/Al2O3 catalysts applied to ethanol steam reforming

Ni/Al₂O₃ catalysts containing 5 wt% of Ni and modified by addition of CaO (0–5 wt%) were tested in ethanol steam reforming reaction in order to reduce the dehydration ethanol reaction, which produces ethylene that may polymerize and produce coke. The catalysts were prepared by impregnation (I) and co-precipitation (C) methods. All catalysts were investigated for ethanol steam reforming and the catalytic performance was compared in terms of additive addition. The catalysts 5Ni–5Ca/Al (I) and 5Ni–5Ca/Al (C) were less selective to ethylene production and therefore were characterized by the following techniques: energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray absorption near edge structure (XANES), specific surface area by the BET method, scanning electron microcopy (SEM) and isopropanol decomposition reaction. By comparing the catalysts, the 5Ni–5Ca/Al (I) catalyst presented the lowest acidity and carbon deposition, and also presented no deactivation in 24 h of catalytic test.     

Preparation and characterization of Ni based catalysts for the catalytic partial oxidation of methane: Effect of support basicity on H2/CO ratio and carbon deposition

The catalytic partial oxidation of methane (CPOM) was studied on Ni based catalysts. Catalysts were prepared by wet impregnation method and characterized by using AAS, BET, XRD, HRTEM, TPR, TPO, Raman Spectroscopy and TPSR techniques. The prepared catalysts showed nearly 95% CH₄ conversion and nearly 96% H₂ selectivity under the flow of 157,500 (L kg⁻¹ h⁻¹) with the ratio of CH₄/O₂ = 2 by using air as an oxidant at 1 atm and 800 °C. Support basicity greatly influenced the H₂/CO ratio and carbon deposition. It was found that the lowest carbon deposition occurred on Ni impregnated MgO catalyst. Considering the results, it was found that Ni/MgO catalyst with 10% Ni content would be the best catalyst amongst Ni/Al₂O₃, Ni/MgO/Al₂O₃, Ni/MgAl₂O₄ and Ni/Sorbacid for the CPOM only under more reductive conditions. Under optimum conditions, Ni/MgO showed poor performance and therefore Ni/Sorbacid would be the ideal catalyst because of its greater carbon resistance than the other catalysts.     

Thermocatalytic decomposition of methane over mesoporous Ni/xMgO·Al2O3 nanocatalysts

This paper describes a facile method to produce mesoporous nanostructure Ni/Al₂O₃, Ni/MgO, and Ni/xMgO.Al₂O₃ (x: MgO/Al₂O₃ molar ratio) catalysts prepared by “one-pot” evaporation-induced self-assembly (EISA) method with some modifications for investigating in the thermocatalytic decomposition of methane. Detailed characterizations of the material were performed with X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and N₂ adsorption/desorption, hydrogen temperature-programmed reduction (H₂-TPR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and temperature-programmed oxidation (TPO). The characterizations demonstrated that the synthesized catalysts with various MgO/Al₂O₃ molar ratios possessed mesoporous structure with the high BET area in the range of 216.79 to 31.74 m² g^?1. The effect of different surfactants and calcination temperatures on the characterizations and catalytic activity of the catalysts were also examined in details. The experimental results showed that the catalysts exhibited high catalytic potential in this process and the 55 wt.% Ni/2 MgO·Al₂O₃ catalyst calcined at 600^οC possessed an acceptable methane conversion (～60%) under the harsh reaction conditions (GHSV = 48000 (mL h^?1 g_cat^?1)).     

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).     

High temperature water gas shift reaction over promoted iron based catalysts prepared by pyrolysis method

In this work the effects of different promoters (Cr, Al, Mn, Ce, Ni, Co and Cu) on the structural and catalytic properties of Nanocrystalline iron based catalysts for high temperature water gas shift reaction were investigated. The catalysts were prepared in active phase (Fe₃O₄) via a facile direct synthesis routs without any additive and characterized using X-ray diffraction (XRD), N₂ adsorption (BET), temperature-programmed reduction (TPR), transmission and scanning electron microscopies (TEM,SEM) techniques. The obtained results indicated that synergic effect of Mn and Ni promoters can lead to obtain a Cr-free catalyst with high activity. In addition, the effect of Ni content on the structural and catalytic properties of the Fe–Mn–Ni catalysts was investigated. It was found that Fe–Mn–Ni catalyst with Fe/Mn = 10 and Fe/Ni = 5 weight ratios showed the highest catalytic activity among the prepared catalysts and possessed a stable catalytic performance without any decrease during 10 h time on stream. Moreover, the effect of GHSV and steam/gas ratio on the catalytic performance of this catalyst was investigated.     

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.     

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.