Stability of Ni and Rh–Ni catalysts derived from hydrotalcite-like precursors for the partial oxidation of methane

In this work, NiMgAl and RhNiMgAl catalysts prepared from HTLCs precursors were investigated for the Partial Oxidation of Methane (POM) at 550 and 750 °C. Samples have been characterized by XRD, TPR, H₂ chemisorption, TPSR analyses, XPS, field emission scanning electron microscopy and Raman spectroscopy. NiMgAl catalysts with high Ni content (40 and 16 wt%) showed high stability and high methane conversion for POM. On the other hand those with lower Ni content (NiHT15 and NiHT25, with 6 and 4 wt%) exhibited low catalytic activity with low H₂/CO ratio (<2) and fast deactivation. In RhNiHT25 (0.6 wt. % Rh), the Ni reducibility was improved, increasing the methane conversion and hydrogen selectivity. In addition, the noticeable increase in stability was related to the absence of carbon deposition after 30 h on stream at 550 °C. These results show that RhNiHT25 is promising for application in membrane reactors to produce high purity hydrogen.     

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.     

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.     

Effect of alkaline earth oxides on nickel catalysts supported over γ-alumina for butanol steam reforming: Coke formation and deactivation process

Nickel catalysts were synthesized by the wet impregnation of three different supports: γ-Al₂O₃ and alumina promoted with either 10 wt % of MgO or 10 wt% of CaO. The catalysts were evaluated in butanol steam reforming at 500 °C, atmospheric pressure, GHSV of 500,000 h⁻¹ and 10% v/v butanol in the feed. Both promoters decreased catalyst acidity and increased basicity. The catalyst promoted with MgO exhibited the lowest acidity (1.1 μmolNH₃ m⁻²), whereas that promoted with CaO, the highest basicity (870.7 μmolCO₂ m⁻²). The promotion with MgO led to the highest hydrogen yield (66%) and stability, associated with its highest nickel dispersion (3.4%), lowest acidity and lowest coke formation normalized by carbon converted (3.0 mmol L mol⁻¹). The catalyst promoted with CaO presented the most severe deactivation, associated with its lowest dispersion (1.0%) and the highest amount of encapsulated coke (3.5 mmol L mol⁻¹).     

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.     

Copper promoted Co/MgO: A stable and efficient catalyst for glycerol steam reforming

Different types of cobalt-based mixed oxide catalysts (20 wt%Co/MgO, 5 wt%Cu-20 wt% Co/MgO, 20 wt%Co/50%MgO–50%Al₂O₃) were synthesized by the co-precipitation method and applied for hydrogen production from glycerol steam reforming. The catalysts were characterized using X-ray diffraction (XRD), H₂-Temperature-programmed reduction (H₂-TPR), CO₂-Temperature Programmed desorption, CO-Chemisorption, and CHN techniques. The H₂-TPR analysis showed the reducibility of cobalt-oxide (5Cu20CM; 5 wt%Cu-20 wt% Co/MgO) was enhanced by the copper, and reduction profiles of cobalt oxide shifted to a lower temperature (<450 °C). Among the catalysts, 5Cu20CM showed a maximum yield of hydrogen (74.6%) with 100% conversion of glycerol to the gaseous phase. The superior catalytic performance of 5Cu20CM for glycerol conversion was attributed to the smaller particle size (7 nm), higher dispersion of cobalt (35.0%), and the higher surface area (56 m²/g) of cobalt metal. Furthermore, Raman spectroscopy of the spent catalysts confirmed that the copper promoted cobalt-magnesium catalyst suppressed the carbon formation, consequently, 5Cu20CM catalyst showed a stable performance up to 30 h.     

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.     

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.     

Comparative study between supported and doped MgO catalysts in supercritical water gasification for hydrogen production

Different catalyst structures may influence the catalytic performance of catalysts in supercritical water gasification (SCWG). This study reports the catalytic activity of supported (SP) and doped (DP) MgO catalysts in catalyzing the gasification of oil palm frond (OPF) biomass in supercritical water to produce hydrogen. Two types of supported catalysts, labelled as Ni-SP (nickel supported MgO) and Zn-SP (zinc supported MgO), were synthesized via impregnation method. Another two types of doped catalysts, labelled as Ni-DP (nickel doped MgO) and Zn-DP (zinc doped MgO), were synthesized by using the self-propagating combustion method. All the synthesized catalysts were found to be pure with the doped catalysts exhibited small crystallites, in comparison to that produced by the supported catalysts. The specific surface area increased in the order of Ni-DP (67.9 m² g⁻¹) > Zn-DP (36.3 m² g⁻¹) > Ni-SP (30.1 m² g⁻¹) > Zn-SP (13.1 m² g⁻¹). Regardless of supported or doped, the Ni-based catalysts always had larger specific surface area than that in the Zn-based catalysts. Unexpectedly, the Zn-based catalysts with smaller surface area for SCWG produced higher hydrogen (H₂) yield from the OPF biomass. When compared to the non-catalytic reaction, the H₂ yield increased by 187.2% for Ni-SP, 269.0% for Zn-SP, 361.7% for Ni-DP, and 438.1% for Zn-DP. Among the studied catalysts, the Zn-DP displayed the highest H₂ yield because it had the highest number of basic sites; approximately twenty-fold higher than that of the Zn-SP catalyst. The Zn-DP also proved to be the most stable catalyst, as verified from the X-Ray photoelectron spectroscopy (XPS) results. As such, this study concludes that the catalytic performances of the synthesized catalysts do not only depend on the specific surface area, but they are also influenced by the number of basic sites and the catalyst stability. It is trustworthy to note that this is the initial study that associated SCWG with doped catalysts. The doped catalysts, hence, may serve as a new catalyst system to generate SCWG reactions.     

Hydrogen production from dairy wastewater using catalytic supercritical water gasification: Mechanism and reaction pathway

The supercritical water gasification (SCWG) of real dairy wastewater (cheese-based or whey) was performed in a batch reactor in presence of two catalysts (MnO₂, MgO) and one additive (formic acid). The operational conditions of this work were at a temperature range of 350–400 C and the residence time of 30–60 min. The catalysts and formic acid were applied in 1 wt%, 3 wt%, and 5 wt% to determine their effect on hydrogen production. The concentrations of catalysts and formic acid were calculated based on the weight of feedstock without ash. The results showed that increased temperature and prolonged residence time contributed to the hydrogen production (HP) and gasification efficiency (GE). The gas yield of hydrogen in the optimum condition (400 C and 60 min) was achieved as 1.36 mmol/gr DAF (dry ash free). Formic acid addition was favored towards enhancing hydrogen content while the addition of metal oxides (MnO₂ and MgO) had an apex in their hydrogen production and they reached the highest hydrogen in 1 wt% concentration then ebbed. Moreover, GE was increased by the addition of the catalysts and formic acid concentrations. The highest hydrogen content (35.4%) was obtained in 1 wt% MnO₂ and the highest GE (32.22%) was attained in the 5 wt% formic acid concentration. A reaction pathway was proposed based on the GC-MS data of feedstock and produced liquid phase at different condition as well as similar studies.     

Autothermal reforming of methane over Ni catalysts supported on nanocrystalline MgO with high surface area and plated-like shape

Autothermal reforming of methane (ATRM), combination of partial oxidation and steam reforming was performed over MgO supported Ni catalysts. The preparation of MgO via surfactant-assisted precipitation method led to obtain a nanocrystalline carrier for nickel catalysts. The results demonstrated that methane conversion is significantly increased with increasing the Ni content (5, 7, 10 and 15%Ni) and methane conversion of 15%Ni/MgO was higher than that of other catalysts with lower Ni loading in all operation temperatures.In addition, increasing the system operation temperatures led to decrease in H₂/CO due to the fact that water-gas shift reaction was thermodynamically unfavorable at elevated temperatures. This catalyst also exhibited stable catalytic performance during 50 h time on stream. Furthermore, the influences of varying GHSV and feed ratio on activity of 15%Ni/MgO catalyst were investigated.     

Hydrogen production by methane decomposition using bimetallic Ni–Fe catalysts

The catalytic methane decomposition is the leading method for CO_x-free hydrogen and carbon nanomaterial production. In the present study, calcium-silicate based bimetallic Ni–Fe catalysts have been prepared and used to decompose the methane content of the ‘product gas’ obtained in the biomass gasification process for increasing total hydrogen production. Al₂O₃ was used as secondary support on calcium silicate based support material where Ni or Ni–Fe were doped by co-impregnation technique. The activity of catalysts was examined for diluted 6% methane-nitrogen mixture in a tubular reactor at different temperatures between 600 °C and 800 °C under atmospheric pressure, and data were collected using a quadrupole mass spectrometer. Catalysts were characterized by XRD, SEM/EDS, TEM, XPS, ICP-MS, BET, TPR, and TGA techniques. The relation between structural and textural properties of catalysts and their catalytic activity has been investigated. Even though the crystal structure of catalysts had a significant effect on the activity, a direct relation between the BET surface area and the activity was not observed. The methane conversion increased by increasing temperature up to 700 °C. The highest methane conversion has been obtained as 69% at 700 °C with F3 catalyst which has the highest Fe addition, and the addition of Fe improved the stability of catalysts. Moreover, carbon nanotubes with different diameter were formed during methane decomposition reaction, and the addition of Fe increased the formation tendency.     

Biogas reforming over La-promoted Ni/SBA-16 catalyst for syngas production: Catalytic structure and process activity investigation

Biogas, a mixture of CO₂/CH₄, is reasonable for conversion to syngas (H₂/CO) by dry methane reforming (DMR) reaction. The modification of Ni/SBA-16 with a lanthanum promoter using the co-impregnation technique is investigated in this study. The temperature of reaction (600–750 °C), La loading (3.85–11.56 wt%), and Ni loading (10–30 wt%) are the parameters that are varied for maximizing reaction conversions. The synthesized catalysts and SBA-16 supporting material were characterized by several methods before and after reaction. According to the analysis, the existence of La₂O₃ particles on the catalyst's surface has decreased the particle sizes, as well as enhanced their dispersion. Therefore, the maximum CH₄ conversion of 94.21%, CO₂ conversion of 90.12%, H₂ yield of 90.53%, and H₂/CO molar ratio of 2.03 are achieved using 20Ni-5.78La/SBA16 at 700 °C. Besides, this catalyst showed lower deposited coke and higher stability compared with other synthesized catalysts.     

Co-precipitated Ni–Mg–Al catalysts for hydrogen production by supercritical water gasification of glucose

Supercritical water gasification (SCWG) is a promising process for hydrogen production from biomass. In this study, a series of Ni–Mg–Al catalysts with different Mg/Al molar ratios has been synthesized by a co-precipitation method for hydrogen production by SCWG of glucose. Effects of Mg addition on the catalytic activity, hydrothermal stability and anti-carbon performance of alumina supported nickel catalyst were investigated. The highly dispersed nickel catalysts prepared by co-precipitation could greatly enhance the gasification efficiency of glucose in supercritical water. Among the tested Ni–Mg–Al catalysts, NiMg_0.6Al_1.9 showed the highest catalytic activity with the hydrogen yield of 11.77 mmol/g (912% as that of non-catalytic test). NiMg_0.6Al_1.9 also showed the best hydrothermal stability probably due to the formation of MgAl₂O₄. Mg could efficiently improve the anti-carbon ability of Ni–Al catalyst by inhibiting the formation of graphite carbon. It is also confirmed that MgO supported nickel catalyst is not suitable for SCWG process owing to the difficulty on nickel oxides reduction in the precursors and the phase change of MgO to Mg(OH)₂ under the hydrothermal condition.     

Water effect in hydrogen production from methane

Ni/MgO and Ni/Al₂O₃ catalysts were prepared, by wet impregnation, to compare their performance in hydrogen production from methane CPO, wet-CPO and SR. The catalytic activity was tested at 1073 K, 1 bar and 600–1200 h⁻¹. Fresh and used catalysts were characterized by different techniques. Both supports, as expected, had a low surface area (27.1 m²/g MgO and 6.2 m²/g α-Al₂O₃), as determined by BET method. The images obtained with SEM and TEM revealed that the Ni was more dispersed in the MgO support than in the Al₂O₃ one. By XRD a strong interaction, as solid-solution, between NiO and MgO was found in the 30Ni/MgO and 40Ni/MgO catalysts. The fresh 40Ni/Al₂O₃ reduced catalyst was partially reduced. But after the activity tests the stability of the reduced Ni became bigger. Some Ni sintering was also observed in the 40Ni/Al₂O₃ after the wet-CPO and SR tests. The behaviour of the three catalysts was very good in CPO methane conversion (90–93%), but the gradual increase of the steam to carbon ratio, wet-CPO and SR, affected negatively the conversion.     

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.     

On the effect of yttrium promotion on Ni-layered double hydroxides-derived catalysts for hydrogenation of CO2 to methane

Ni-containing mixed oxides derived from layered double hydroxides with various amounts of yttrium were synthesized by a co-precipitation method at constant pH and then obtained by thermal decomposition. The characterization techniques of XRD, elemental analysis, low-temperature N₂ sorption, H₂-TPR, CO₂-TPD, TGA and TPO were used on the studied catalysts. The catalytic activity of the catalysts was evaluated in the CO₂ methanation reaction performed at atmospheric pressure. The obtained results confirmed the formation of nano-sized mixed oxides after the thermal decomposition of hydrotalcites. The introduction of yttrium to Ni/Mg/Al layered double hydroxides led to a stronger interaction between nickel species and the matrix support and decreased nickel particle size as compared to the yttrium-free catalyst. The modification with Y (0.4 and 2 wt%) had a positive effect on the catalytic performance in the moderate temperature region (250–300 °C), with CO₂ conversion increasing from 16% for MO-0Y to 81% and 40% for MO-0.4Y and MO-2.0Y at 250 °C, respectively. The improved activity may be correlated with the increase of percentage of medium-strength basic sites, the stronger metal-support interaction, as well as decreased crystallite size of metallic nickel. High selectivity towards methane of 99% formation at 250 °C was registered for all the catalysts.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over mesoporous Ni-La-Al2O3 aerogel catalysts: Effect of La content

Mesoporous Ni-La-Al₂O₃ aerogel catalysts (denoted as (40-x)NixLa) with different lanthanum content (x) were prepared by a single-step sol-gel method and a subsequent CO₂ supercritical drying method. The effect of lanthanum content on the physicochemical properties and catalytic performance of mesoporous (40-x)NixLa catalysts in the steam reforming of liquefied natural gas (LNG) was investigated. Physicochemical properties of (40-x)NixLa catalysts were strongly influenced by lanthanum content. Dispersion and reducibility of nickel aluminate phase in the (40-x)NixLa catalysts increased with increasing lanthanum content. Small amount of lanthanum addition was effective for dispersion of metallic nickel in the (40-x)NixLa catalysts, but large amount of lanthanum addition was not favorable for nickel dispersion due to the blocking of active sites. In the steam reforming of LNG, both LNG conversion and hydrogen yield showed volcano-shaped curves with respect to lanthanum content. Average nickel diameter of (40-x)NixLa catalysts was well correlated with LNG conversion and hydrogen yield over the catalysts. Among the catalysts tested, 36Ni4La (36 wt% Ni and 4 wt% La) catalyst with the smallest average nickel diameter exhibited the best catalytic performance and the strongest resistance toward carbon deposition in the steam reforming of LNG.     

Effect of metal additives on the catalytic performance of Ni/Al2O3 catalyst in thermocatalytic decomposition of methane

Thermocatalytic decomposition of methane is proposed to be an economical and green method to produce CO_x-free hydrogen and carbon nanomaterial. In present work, 60 wt% Ni/Al₂O₃ catalysts with different additives (Cu, Mn, Pd, Co, Zn, Fe, Mg) were prepared by co-impregnation method to investigate promotional effects of these metal additives on the activity and stability of 60 wt% Ni/Al₂O₃ and find out a really effective promoter for decomposition of methane. The catalyst was characterized by N₂ adsorption/desorption, X-ray diffraction, scanning electron microscopy, inductively coupled plasma optical emission spectrometer and hydrogen temperature programmed reduction. While metal additives (5 wt%) were added into 60 wt% Ni/Al₂O₃, the activity stability of 60 wt% Ni/Al₂O₃ was improved and the CH₄ conversion of 60 wt% Ni/Al₂O₃ was also improved except Zn addition. Mn addition was found to improve the catalytic activity of 60 wt% Ni/Al₂O₃ significantly and the CH₄ conversion of 5 wt% Mn-60 wt% Ni/Al₂O₃ was ∼80%. Cu addition was found to remarkably improve the catalytic stability of 60 wt% Ni/Al₂O₃ and the CH₄ conversion of 5 wt% Cu-60 wt% Ni/Al₂O₃ decreased from 61% to 45% after 250 min of reaction time. Carbon nanomaterials formed in the thermocatalytic decomposition process were characterized by X-ray diffraction, scanning electron microscopy, thermal gravimetric analyzer and Raman spectroscopy. Carbon deposits consist of amorphous carbon and carbon nanofibers.     

Reduction time effect on structure and performance of Ni–Co/MgO catalyst for carbon dioxide reforming of methane

Reducing catalysts with hydrogen is an important process for carbon dioxide reforming methane since metallic active sites are exposed and dispersed during the reduction process. In this work, Ni–Co/MgO catalysts were prepared for syngas production by using a multiple-impregnation method with a carbon dioxide reforming methane reaction. Activity evaluation showed that catalysts that reduced for 1 h exhibited superior catalytic activity with methane and carbon dioxide conversion at 92% and 97%, respectively, and the syngas ratio close to unity (0.98). The high activity is ascribed to the better metal dispersion (10.5%) and smaller active metal particle size (10 nm). Raman spectra analysis indicated that catalysts that reduced for a longer time possessed larger active metal particle size, and were more susceptible to the formation of graphite-like carbon deposits, which were difficult to be removed by the active oxygen species derived from carbon dioxide dissociation.