Effect of preparation method of mesoporous Ni–Al2O3 catalysts on their catalytic activity for hydrogen production by steam reforming of liquefied natural gas (LNG)

Mesoporous Ni–Al₂O₃ catalysts were prepared by impregnation method (NiAl-IP), co-precipitation method (NiAl-CP), and sequential precipitation method (NiAl-SP) for use in hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of preparation method of mesoporous Ni–Al₂O₃ catalysts on their catalytic activity for steam reforming of LNG was investigated. Physicochemical properties of Ni–Al₂O₃ catalysts were strongly influenced by the preparation method of Ni–Al₂O₃ catalysts. Surface area, pore volume, and average pore size of Ni–Al₂O₃ catalysts decreased in the order of NiAl-SP > NiAl-CP > NiAl-IP. Nickel species strongly interacted with Al₂O₃ supports through the formation of nickel aluminate phase. Surface nickel aluminate phase of Ni–Al₂O₃ catalysts was readily reduced after the reduction process, while bulk nickel aluminate phase of NiAl-CP catalyst was hardly reducible. Nickel dispersion and nickel surface area of Ni–Al₂O₃ catalysts decreased in the order of NiAl-SP > NiAl-CP > NiAl-IP. Among the catalysts tested, NiAl-SP catalyst with the highest nickel surface area showed the best catalytic performance in the steam reforming of LNG. Furthermore, finely dispersed nickel species in the NiAl-SP catalyst efficiently suppressed the carbon deposition during the reaction.     

Effect of Ni/Al atomic ratio of mesoporous Ni–Al2O3 aerogel catalysts on their catalytic activity for hydrogen production by steam reforming of liquefied natural gas (LNG)

Mesoporous Ni–Al₂O₃ (XNiAE) aerogel catalysts with different Ni/Al atomic ratio (X) were prepared by a single-step sol-gel method and a subsequent CO₂ supercritical drying method. The effect of Ni/Al atomic ratio of mesoporous XNiAE aerogel catalysts on their physicochemical properties and catalytic activity for steam reforming of liquefied natural gas (LNG) was investigated. Textural properties and chemical properties of XNiAE catalysts were strongly influenced by Ni/Al atomic ratio. Nickel species were highly dispersed on the surface of XNiAE catalysts through the formation of surface nickel aluminate phase. In the steam reforming of LNG, both LNG conversion and hydrogen yield showed volcano-shaped curves with respect to Ni/Al atomic ratio. Average nickel diameter of XNiAl catalysts was well correlated with LNG conversion and hydrogen yield over the catalysts. Among the catalysts tested, 0.35NiAE (Ni/Al = 0.35) catalyst with the smallest average nickel diameter showed the best catalytic performance. The highest surface area, the largest pore volume, the largest average pore size, and the highest reducibility of 0.35NiAE catalyst were also partly responsible for its superior catalytic performance.     

Stability improvements of Ni/α-Al2O3 catalysts to obtain hydrogen from methane reforming

Ni catalysts supported on commercial α-Al₂O₃ modified by addition of CeO₂ and/or ZrO₂ were prepared in the present work. Since the principal objective was to evaluate the behavior of these systems and the support effect on the stability, methane reforming reactions were studied with steam, carbon dioxide, partial oxidation and mixed reforming. Results show that catalysts supported on Ce–Zr–α-Al₂O₃ composites present better reforming activity and stability noticeably higher than in the case of the reference support. With respect to composites, the presence of mixed oxides of Ce_xZr_1−xO₂ type facilitates the formation of active phases with higher interaction. This fact reduces the deactivation by sintering conferring to the system a higher contribution of adsorbed oxygen species, favoring the deposited carbon elimination. These improvements resulted in being dependent on the Ce:Zr ratio of the composite, thus obtaining more stable catalysts for Ce:Zr = 4:1 ratios.     

CO2 reforming of methane on Ni/γ-Al2O3 catalyst prepared by dielectric barrier discharge hydrogen plasma

Ni/γ-Al₂O₃ catalyst was prepared by direct treatment of Ni(NO₃)₂/γ-Al₂O₃ precursor with dielectric barrier discharge (DBD) hydrogen plasma at different input powers, characterized by XRD, H₂-TPR, CO₂-TPD, N₂ adsorption and TEM, respectively, and used as the catalyst for CO₂ reforming of methane (CRM). The results showed that the input power obviously affected the reduction degree and catalytic performances of catalysts. Low input power under 40 W mainly resulted in the decomposition of nickel nitrate into Ni oxides. The reduction degree, catalytic activity and stability increase with the input power. Similar catalytic performances in CRM reaction can be obtained when the power exceeds 80 W. Compared with the Ni/Al₂O₃ catalyst prepared by traditional method, Ni/γ-Al₂O₃ samples prepared by H₂ DBD plasma exhibit better activities, stability and anti-carbon deposit performances. It is mainly ascribed to smaller Ni particle size, more basic sites and weaker basicity. The increase of Ni particle sizes due to the sintering at high temperature results in the decrease of catalytic activities and coke formation.     

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.     

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.     

Performance characteristics of Mo–Ni/Al2O3 catalysts in LPG oxidative steam reforming for hydrogen production

A 1:1 propane–butane mixture was used to study the effect of promoting 15 wt.% Ni/Al₂O₃ (15Ni) catalyst with small amounts of Mo (0.05, 0.1, 0.3, and 0.5 wt.%) for H₂ production during LPG oxidative steam reforming. Stability tests at 450 °C showed that lower Mo loadings (0.1 and 0.05 wt.%) had higher conversions and H₂ production rates than the non-promoted catalyst and a stable performance for the whole 18-h test period. TPO results showed that slightly more Ni sites were available for whisker formation over the Mo catalyst with 0.1 wt.% loading, the types of carbon resulting from cracking were the same on both promoted and non-promoted catalysts. Higher Mo loaded catalysts (0.3 and 0.5 wt.%) showed higher H₂ yields than the non-promoted catalysts, but lower feed-fuel conversions. XRD revealed that the loss in activity was due to oxidation of active Ni species to inactive Ni and Ni–Mo.     

Glycerol steam reforming over Ni/mg/γ-Al2O3 catalysts effect of Ni(II) content

The aim of the present work is to analyse the effect of the Ni(II) content for the Ni(II)-Mg(II)/γ-Al₂O₃ catalysts on the textural and structural characteristics of the solid, as well on the catalytic activity and selectivity to H₂ for the steam reforming of glycerol at atmospheric pressure.     

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

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

Boosting hydrogen production by ethanol steam reforming on cobalt-modified Ni–Al2O3 catalyst

Ethanol steam reforming (ESR) is one of the most promising reliable and recyclable technologies for hydrogen production. However, the development of robust, efficient Ni-based catalysts that minimize metal sintering and carbon deposition remains a key challenge. The influence of cobalt loading and ESR conditions on H₂ selectivity and catalytic stability is the focus of this study. Ni–Co/Al₂O₃ catalysts with various Co percentages were prepared by the co-impregnation method and complementary characterization tests were performed. Among the catalysts tested, Ni–Co/Al₂O₃ (5 wt% Co) exhibited the smallest metal crystallite size, the highest surface area, and the best catalytic performance. Thereafter, the effects of temperature, LHSV and S:C molar ratio were studied. 100% ethanol conversion and maximum H₂ selectivity (95.14%) were reached at 600 °C, 0.05 L/g_cat.h and S:C molar ratio of 12:1. Furthermore, ethanol turnover frequency (TOF) was computed for each catalyst. TOF results showed that the Ni–Co interaction had an impact on the catalytic activity. Finally, Ni2CoAl was subjected to 50-h stability test and only 6.12 mg_carbon/g_cat.h coke deposition was observed.     

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.     

Effect of CaO–ZrO2 addition to Ni supported on γ-Al2O3 by sequential impregnation in steam methane reforming

Ni catalysts supported on (CaO–ZrO₂)-modified γ-Al₂O₃ were prepared by sequential impregnation. The effects of varied CaO to ZrO₂ mole ratios at 0, 0.20, 0.35, 0.45, and 0.55 on the activity and stability of the modified Ni catalysts were studied. As a result of using CaO–ZrO₂ as a promoter, each catalyst contained CaO–ZrO₂ at only 5%. γ-Al₂O₃ used as support was modified by CaO–ZrO₂ before the deposition of nickel oxide. The addition of CaO–ZrO₂ at an optimum ratio was expected to improve the stability of Ni catalysts due to the decrease of carbon formation resulting from carbon gasification. All the fresh catalysts were characterized by ICP, XRD, BET surface area, TGA in H₂, and TPR before catalytic testing in steam methane reforming at 600 °C. The spent catalysts were examined by TEM and TGA to observe the catalysts deactivation. The identification of CaO–ZrO₂ phases indicated that CaO and ZrO₂ reacted with each other to be monoclinic solid solution ZrO₂, CaZr₄O₉, CaZrO₃, and CaO corresponding to the phase diagram of CaO–ZrO₂. The existence of CaZrO₃ for 0.55 mol ratio of CaO/ZrO₂ enhanced activity in steam methane reforming because oxygen vacancies in CaZrO₃ greatly preferred the water adsorption creating the favorable conditions for carbon gasification and, then, water gas shift. The prominence and continued existence of these two reactions on the Ni catalysts leads to the particular increase of H₂ yield. Moreover, the increasing amount of CaZrO₃ in the Ni catalysts significantly improved carbon gasification. However, the Ni catalysts with CaZrO₃ showed whisker carbon after catalytic testing; this carbon specie has not been tolerated in steam methane reforming. Therefore, these results significantly differed from the hypothesis.     

Production of hydrogen via steam reforming of biofuels on Ni/CeO2–Al2O3 catalysts promoted by noble metals

The catalytic activity of Ni/CeO₂–Al₂O₃ catalysts modified with noble metals (Pt, Ir, Pd and Ru) was investigated for the steam reform of ethanol and glycerol. The catalysts were characterized by the following techniques: Energy-dispersive X-ray, BET, X-ray diffraction, temperature-programmed reduction, UV–vis diffuse reflectance spectroscopy and X-ray absorption near edge structure (XANES). The results showed that the formation of inactive nickel aluminate was prevented by the presence of CeO₂ dispersed on alumina. The promoting effect of noble metals included a decrease in the reduction temperatures of NiO species interacting with the support, due to the hydrogen spillover effect. It was seen that the addition of noble metal stabilized the Ni sites in the reduced state along the reforming reaction, increasing the ethanol and glycerol conversions and decreasing the coke formation. The higher catalytic performance for the ethanol steam reforming at 600 °C and glycerol steam reforming was obtained for the NiPd and NiPt catalysts, respectively, which presented an effluent gaseous mixture with the highest H₂ yield with reasonably low amounts of CO.     

Catalytic steam reforming of bio-oil aqueous fraction for hydrogen production over Ni–Mo supported on modified sepiolite catalysts

Hydrogen will be an important energy carrier in the future and hydrogen production has drawn a great deal of attention to its advantages in efficiency and environmental benefit. Catalytic steam reforming in this study was carried out in a fixed bed tubular reactor with sepiolite catalysts. Sepiolite catalysts modified with nickel (Ni) and molybdenum (Mo) were prepared using the precipitation method. Influential parameters such as temperature, catalyst, steam to carbon ratio (S/C), the feeding space velocity (WHSV), reforming length, and activity of catalyst were investigated and the yields of H₂, CO, CH₄, and CO₂ were obtained. The result of this experiment shows that the acidified sepiolite catalyst with addition of the Ni and Mo greatly improves the activities of catalyst and effectively increases the yield of hydrogen. The favorable reaction condition is as follows: reaction temperature is 700–800 °C; S/C is 16–18; the feeding space velocity is 1.5–2.2 h⁻¹, respectively.     

Hydrogen production from steam reforming of bioethanol using Cu/Ni/K/γ-Al2O3 catalysts. Effect of Ni

Hydrogen to be used as a raw material in fuel cells or even as a direct fuel can be obtained from steam reforming of bioethanol. The key aim of this process is to maximize hydrogen production, discouraging at the same time those reactions leading to undesirable products, such as methane, acetaldehyde, diethyl ether or acetic acid, that compete with H₂ for the hydrogen atoms. Cu–Ni–K/γ-Al₂O₃ catalysts are suitable for this reaction since they are able to produce acceptable amounts of hydrogen working at atmospheric pressure and a temperature of 300°C. The effect of nickel content in the catalyst on the steam-reforming reaction was analyzed. Nickel addition enhances ethanol gasification, increasing the gas yield and reducing acetaldehyde and acetic acid production.     

Ni–Co bimetallic MgO-based catalysts for hydrogen production via steam reforming of acetic acid from bio-oil

Acetic acid (AC) is a representative compound of bio-oil via fast pyrolysis of biomass, and can be processed for hydrogen production via steam reforming (SR). In the current work, the Ni_xCo_1−xMg₆O_7±δ (x = 0–1) bimetallic catalysts were prepared via co-precipitation and impregnation, and tested in SR of AC. The reaction results indicate that the monometallic catalysts were deactivated obviously in SR, while the Ni_0.2Co_0.8Mg₆O_7±δ bimetallic catalyst performed better in both activity and stability: not only the conversion of AC remained stable near 100%, but also the H₂ yield maintained stable near 3.1 mol-H₂/mol-AC. The results of XRD, BET, XPS, TG and TEM indicate that the high catalytic performance of the Ni_0.2Co_0.8Mg₆O_7±δ catalyst can be attributed to 1) resistance to oxidation of active metals, 2) resistance to coking, and 3) stability of structure and electronic properties.     

Hydrogen production from catalytic steam reforming of bio-oil aqueous fraction over Ni/CeO2–ZrO2 catalysts

A series of composite catalysts Ni/CeO₂–ZrO₂ were prepared via impregnation method with Ni as the active metal. A laboratory-scale fixed-bed reactor was employed to investigate the catalyst performance during hydrogen production by steam reforming bio-oil aqueous fraction. Effects of water-to-bio-oil ratio (W/B), reaction temperature, and the loaded weight of Ni and Ce on the hydrogen production performance of Ni/CeO₂–ZrO₂ catalysts were examined. The obtained results were compared with commercial nickel-based catalysts (Z417). The best performance of Ni/CeO₂–ZrO₂ catalyst was observed when the Ni and Ce loaded weight were 12% and 7.5% respectively. At W/B = 4.9, T = 800 °C, H₂ yield reaches the highest of 69.7% and H₂ content of 61.8% were obtained. Under the same condition, H₂ yield and H₂ content were higher than commercial nickel-based catalysts (Z417).     

Effect of N2O-mediated calcination on nickel species and the catalytic activity of nickel catalysts supported on γ-Al2O3 in the steam reforming of glycerol

The steam reforming of glycerol over supported nickel catalysts is a promising and cost-effective method for producing hydrogen. The activity of nickel catalysts supported on γ-Al₂O₃ is low, primarily due to the formation of inactive nickel species during high temperature calcination in air. In order to address this problem, a Ni/γ-Al₂O₃ catalyst was prepared by calcination at 700 °C in a nitrous oxide (N₂O) environment. The N₂O calcined catalyst showed an enhanced activity for the steam reforming of glycerol. A variety of characterization techniques (XRD, TPR, XPS and H₂ Chemisorption) confirmed that the high temperature N₂O calcination resulted in a significant decrease in the levels of nickel aluminate. The N₂O calcination also led to an enhancement in the amount of NiO as well as nickel ions present on the surface of the catalyst. Interestingly, compared to an air calcined catalyst, the N₂O calcined catalyst contained larger nickel particles after reduction but the N₂O calcined catalyst had a much larger nickel surface area and dispersion, which resulted in higher glycerol conversion and hydrogen yield.     

Influence of the acid–base properties over NiSn/MgO–Al2O3 catalysts in the hydrogen production from glycerol steam reforming

In this work we have investigated the hydrogen production from glycerol steam reforming. The effect of the acid–base properties was evaluated using four catalysts based in an alloy Ni–Sn as active phase supported over γ-Al₂O₃ with different content in MgO, varying between 0 and 30 wt.% The incorporation of MgO results in the formation of MgAl₂O₄ spinel, which modifies the acid–base properties of the catalyst. Addition of MgO favored the glycerol conversion into gas, and the catalyst loaded with 10 wt.% MgO exhibited better catalytic performance and higher stability. A blank test with quartz was performed indicating that pyrolysis of glycerol takes place in the quartz.     

Catalysts based on Co-Birnessite and Co-Todorokite for the efficient production of hydrogen by ethanol steam reforming

Two structured manganese oxides (Birnessite and Todorokite) containing Co have been studied in the steam reforming of ethanol. It has been found that both materials are active in the hydrogen production, exhibiting high values of conversion of ethanol and selectivities to hydrogen (100% and 70%, respectively). The best results have been obtained with the catalyst based on Todorokite material. Characterization by DRX, BET area, TPR and TEM has allowed to find that the excellent performance exhibited by this material could be attributed to the lower size of the Co metallic particles present in this sample (6 nm vs 12 nm in Birnessite). This lower size could be related to the especial microporous structure of Todorokite precursor, which could provide high-quality positions for the stabilization of the Co metal particles during calcination and reduction steps. Catalytic deactivation has also been considered. Deactivation was found higher for Todorokite-based catalyst, which presented the largest amount of deposited carbon (26.2 wt% for Co-TOD vs 10.6 wt% for Co-BIR). On the other hand, the degree of metal sintering was found similar in both catalysts. Therefore, the deactivation of the catalysts has been attributed primarily to the deposition of coke. The results presented here show that it is possible to prepare new catalysts based on manganese oxides with Birnessite and Todorokite structure and promoted with Co with high catalytic performance in the steam reforming of ethanol.