Supported Nickel Catalysts Research Articles

Effect of metal–support interactions in Ni/Al2O3 catalysts with low metal loading for methane dry reforming

Nickel catalysts prepared by a variety of different methods are commonly used for reforming reactions such as methane dry reforming. Two preparation methods, controlled adsorption and dry impregnation, are implemented to explore the effect of preparation method on the formation of active sites on alumina supported nickel catalysts. By varying only the preparation method, comparison of catalysts that differ primarily in metal–support interactions, strong metal–support interaction (controlled adsorption) and weak metal–support interactions (dry impregnation), are obtained. For controlled adsorption, optimal synthesis conditions are identified using point of zero charge measurements, pH-precipitation experiments, and adsorption isotherms. Using these conditions, a catalyst with a higher dispersion and strong metal–support interactions is prepared. Physicochemical characterization by N2 physisorption, H2 chemisorption, temperature programmed reduction (TPR), transmission electron microscopy (TEM), and environmental TEM (ETEM) shows that the types of nickel sites formed strongly depend on the synthesis method. Methane dry reforming reactivity studies show stable catalytic performance for at least 9h and provide additional insight into the types of active centers present. After reductive pretreatment, the nickel catalyst prepared by dry impregnation is found to primarily have nickel present as a surface NiAl2O4. In contrast, the active centers for the nickel catalyst prepared by controlled adsorption consist of nickel particles that are encapsulated by a nickel aluminate layer with 1–2nm in thickness. Combustion analysis and XPS of spent catalysts reveal different amounts and nature of carbonaceous deposits as a function of the synthesis method.

Alumina modified by niobia supported nickel catalysts for hydrodechlorination of 1,2-dichloroethane

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Flash pyrolysis of myristic acid adsorbed on supported nickel catalysts for biofuel production

The present work is part of a more general project aiming at studying the decomposition products formed during the pyrolysis of fatty compounds adsorbed on solid catalysts. It deals with the decomposition of myristic acid in contact with nickel-supported catalysts. The pyrolysis was performed at 650 °C in a flash mode. The products were analyzed on-line through a GCMS setup. The catalysts were prepared by impregnation with nickel nitrate, dried at 110 °C and heat treated at 600 °C before use. Solid myristic acid was added at room temperature to the dehydrated catalyst by mechanical mixing followed by heat treatment at 120 °C under intense manual mixing, in order to allow the liquid myristic acid to wet the catalyst surface. The catalysts precursors and the catalysts containing myristic acid were characterized by DTG, and the catalysts in their oxide form were characterized by TPR and XRD. The catalysts containing adsorbed myristic acid were also characterized by FTIR. Compared with Ni/silica producing a high amount of linear 1-olefins during flash pyrolysis, the contents of deoxygenated products, of poly olefins and aromatics, were higher with the Ni/alumina catalyst. The presence of carboxylic acids with a chain length between 6 and 12 C in the pyrolysis products on the Ni/silica catalyst suggests that the cracking along the carbon chain occurred parallel to reactions of decarbonylation and decarboxylation. We also found a direct demethylation route with the Ni/silica catalyst in this experiment.

Sol–gel synthesis of titanium oxide supported nickel catalysts for hydrogen and carbon production by methane decomposition

TiO2-supported NiO hybrids have been synthesized by the sol–gel method and further processed into catalysts for hydrogen production by methane decomposition. The structures of the metal oxides and catalysts are characterized using field emission electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy and N2 adsorption-desorption test. The catalytic performance of the catalysts is evaluated in terms of hydrogen yield rate, methane conversion and carbon yield. It is found that the TiO2-supported catalysts show better catalytic performance when compared with the unsupported catalyst, which is attributed to the uniform dispersion of ultrafine nickel particles as well as the appropriate metal-support interaction. The catalyst performance is dependent on the ratio of NiO and TiO2. The 1NiO–2TiO2 exhibits the highest carbon yield of 321.1 g C g−1 Ni at 500 °C. The structures of the produced carbons are characterized by transmission electron microscopy and X-ray diffraction. It is found that the resulting filamentous carbon materials exhibit uniform diameters and various morphologies including hollow tube, platelet, bow-like and herringbone structures.

Oxidative steam reforming of isobutanol over Ni/γ-Al2O3 catalysts: A comparison with thermodynamic equilibrium analysis

Present work provides a systematic investigation of oxidative steam reforming (OSR) and comparisons with steam reforming (SR) of isobutanol over γ-Al2O3 supported nickel catalysts. Catalysts characterization results demonstrated that majority of nickel oxide was present as dispersed NiAl2O4. The hydrogen yield and selectivity to CO and methane were somewhat lesser for OSR compared to SR. The H2/CO mole ratio in the range of 8–10 was observed under the experimental conditions. The experimental results were matched well with equilibrium products compositions. The spent catalysts were further characterized to elucidate chemical and morphological changes of the catalysts during SR and OSR.

Synthesis of a yolk/shell Fe3O4@poly(ionic liquid)s-derived nitrogen doped graphitic porous carbon materials and its application as support for nickel catalysts

The synthesis of yolk/shell spheres including a movable magnetic core, a poly(ionic liquid)s-derived porous carbon shell, and nickel nanoparticles confined within the porous shell is reported.

Effect of molybdenum carbide concentration on the Ni/ZrO2 catalysts for steam-CO2 bi-reforming of methane

This work presents an efficient approach to enhance the catalytic activity and stability of supported nickel catalysts for steam-CO2 bi-reforming of methane to synthesis gas by introducing the appropriate amount of molybdenum carbide.

Stable hydrogen production from ethanol through steam reforming reaction over nickel-containing smectite-derived catalyst.

Hydrogen production through steam reforming of ethanol was investigated with conventional supported nickel catalysts and a Ni-containing smectite-derived catalyst. The former is initially active, but significant catalyst deactivation occurs during the reaction due to carbon deposition. Side reactions of the decomposition of CO and CH4 are the main reason for the catalyst deactivation, and these reactions can relatively be suppressed by the use of the Ni-containing smectite. The Ni-containing smectite-derived catalyst contains, after H2 reduction, stable and active Ni nanocrystallites, and as a result, it shows a stable and high catalytic performance for the steam reforming of ethanol, producing H2.

ChemInform Abstract: The 2014 Murray Raney Award Lecture: Architecture and Preparation of Supported Nickel Catalysts

AbstractReview: 42 refs.

Steam Reforming of Tar Model Compounds Over Nickel Catalysts Supported on Barium Hexaaluminate

Barium hexaaluminate was prepared by coprecipitation method and used as support for nickel catalysts, with 7 and 14 wt% of NiO. After calcination at 1,200 °C the hexaaluminate support consisted of different crystalline phases with specific surface area of 22 m2 g−1. The catalysts exhibited nickel reduction peaks in the range of 400–540 °C. The catalysts were evaluated in steam reforming of different tar model compounds: benzene, toluene and naphthalene (in solution with toluene). The conversions obtained in benzene and toluene reforming at 650 °C were quite similar, while naphthalene is much more difficult to be converted and inhibits toluene conversion at 800 °C. Both catalysts showed good stability with time on stream despite the high amount of carbon deposit. The coke amount and morphology are dependent on the nature of aromatic compound. .

Mesoporous zirconia-modified clays supported nickel catalysts for CO and CO2 methanation

The Ni catalysts supported on a new structure with zirconia nanoparticles highly dispersed on the partly damaged clay layers has been prepared by the incipient wetness impregnation method and the new structure of the support has been prepared in one pot by the hydrothermal treatment of the mixture of the clay suspension and the ZrO(NO3)2 solution. The catalytic performances for the CO and CO2 methanation on the catalysts have been investigated at a temperature range from 300 °C to 500 °C at atmospheric pressure. The catalysts and supports have been characterized by X-ray diffraction (XRD), transmittance electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), nitrogen adsorption–desorption, and thermogravimetry and differential thermal analysis (TG-DTA). It is found that the zirconia-modified clays have the typical bimodal pore size distribution. Most of the pores with the sizes smaller than 10 nm are resulted from the zirconia pillared clays and the mesopores with the sizes larger than 10 nm and the macropores with the sizes larger than 50 nm are resulted from the partly damaged clay layers. The bimodal pore structure is beneficial to the dispersion of Ni on the layers of the zirconia-modified clays and the increase in Ni loading. The zirconia nanoparticles are highly dispersed on the partly damaged clay layers. Nickel oxide in cubic phase is the only Ni species that can be detected by XRD. The nickel oxide nanoparticles with the sizes of 12 nanometers or more are well dispersed on the zirconia-modified clay layers, which are observed to be buried in the stack layers of zirconia. The presence of nickel oxide in six different forms could be perceived on the new structure. Five of them except the Ni species that forms the spinel phase with Al in clays can be reduced to the active Ni species for the CO and CO2 methanation. But the activity of the Ni species is different, which is associated with the chemical environment at which the Ni species is located. The catalyst with the higher zirconia content, which also has the larger specific surface area and pore volume, exhibits the better catalytic performance for the CO or CO2 methanation. Zirconia in the catalyst is responsible for the dispersion of the Ni species, and it prevents the metallic Ni nanoparticles from sintering during the process of the reaction. In addition, it is also responsible for the reduction of the inactive carbon deposition. The catalyst with 15 wt.% zirconia content has the highest CO conversion of about 100% and the highest methane selectivity of about 93% at 450 °C for CO methanation, and the catalyst with 20% zirconia content has the CO2 conversion of about 80% and the highest methane selectivity of about 99% for CO2 methanation at 350 °C. The catalyst with 15 wt.% zirconia possesses promising stability and no distinct deactivation could be perceived after reaction for 40 h. This new catalyst has great potential to be used in the conversion of the blast furnace gas (BFG) and the coke oven gas (COG) to methane.

The Influence of a Second Metal on the Ni/SiC Catalyst for the Methanation of Syngas

The catalytic performance of silicon carbide supported nickel catalysts modified with or without second metal (Co, Cu and Zn) for the methanation of CO has been investigated in a fixed-bed reactor using a feed consisting of 25% CO and 75% <TEX>$H_2$</TEX> without any diluent gas. It has been found that the introduction of Co species can clearly improve the catalytic activity of Ni/SiC catalyst, whereas the addition of Cu or Zn can result in a significant decrease in the catalytic activity. The characterizations by means of XRD, TEM, XPS, CO-TPD and <TEX>$H_2$</TEX>-TPR indicate that the addition of Co could decrease the particle size of active metal, increase active sites on the surface of methanation catalyst, improve the chemisorption of CO and enhance the reducibility of methanation catalysts. Additionally, the special interaction between Co species and Ni species is likely favorable for the dissociation of adsorbed CO on the surface of catalyst, and this may also contribute to the high activity of 5Co-Ni/SiC catalyst for CO methanation reaction. For 5Cu-Ni/SiC catalyst and 5Zn-Ni/SiC catalyst, Cu and Zn species could cover partial nickel particles and decrease the chemisorption amount of CO. These could be responsible for the low methanation activity. In addition, a 150h stability test under 2 MPa and <TEX>$300^{\circ}C$</TEX> showed that 5Co-Ni/SiC catalyst was very stable for CO methanation reaction.

Hydrogen Production by Methane Dry Reforming on Supported Nickel Catalysts – Enhanced Stability of the Reforming Process

Dry reforming reaction of CH4 by CO2 was carried out over alumina-supported Ni catalysts. Main products were H2 and CO with small amount of H2O by-production because of reverse water gas shift reaction. The activity was gradually decreased with time on stream by carbon deposition. The addition of Ce component was investigated to improve the catalyst stability. The Ce addition brought decrease of carbon deposition during the reaction. The role of Ce has been considered that an inactive coke formation is significantly suppressed.

Catalytic performance of cement clinker supported nickel catalyst in glycerol dry reforming

The paper reports the development of cement clinker-supported nickel (with metal loadings of 5 wt%, 10 wt%, 15 wt% and 20 wt%) catalysts for glycerol dry (CO2) reforming reaction. XRF results showed that CaO constituted 62.0% of cement clinker. The physicochemical characterization of the catalysts revealed 32-folds increment of BET surface area (SBET) with the addition of nickel metal into the cement clinker, which was also corroborated by FESEM images. Significantly, XRD results suggested different types of Ni oxides formation with Ni loading, whilst Ca3SiO5 and Ca2Al0.67Mn0.33FeO5 were the main crystallite species for pure cement clinker. Temperature-programmed reduction analysis yielded three domains of H2 reduction peaks, viz. centered at approximately 750 K referred to as type-I peaks, another peaks at 820 K denoted as type-II peaks and the highest reduction peaks, type-III recorded at above 1000 K. 20 wt% Ni was found to be the best loading with the highest XG and H2 yield, whilst the lowest methanation activity. Syngas with lower H2/CO ratios (0.6 to 1.5) were readily produced from glycerol dry reforming at CO2-to-Glycerol feed ratio (COR) of unity. Nonetheless, carbon deposit comprised of whisker type (Cv) and graphitic-like type (Cc) species were found to be in majority on 20 wt%Ni/CC catalysts.

Deactivation of supported nickel catalysts during CO methanation

Deactivation of Ni-based catalysts was investigated during CO methanation over different supported catalysts. X-ray diffraction and temperature-programmed hydrogenation analyses were used to investigate nickel particle sintering and carbon formation during the first 24h on stream. Titania-supported catalysts presented high resistance towards carbon deposition and nickel particle growth in comparison with the other tested catalysts. Particle size effects on these two deactivation causes were also evaluated. It was shown that carbon formation rates are higher on bigger crystal particles. However, it was found that titania-supported nickel catalysts reduced at high temperatures show the opposite effect. This difference is most probably due to a stronger interaction between nickel and TiOx (x<2) species on smaller crystals which changes the CO dissociation properties and, in consequence, carbon formation rates.

Synthesis, structure and catalytic activity of the supported Ni catalysts for highly efficient one-step hydrogenation of 1,5-dinitronaphthalene to 1,5-diaminodecahydronaphthalene

A series of the supported nickel catalysts have been synthesized through impregnation, characterized by X-ray diffraction, N2 sorption measurement, temperature programmed H2 reduction and X-ray photoelectron spectroscopy. The morphology and particle size of catalysts are imaged by scanning electron microscope. The catalysts have efficiently catalyzed the one-step hydrogenation of 1,5-dinitronaphthalene to 1,5-diaminodecahydronaphthalene. The catalyst 10%Ni/SiO2-1a is the most active for the titled hydrogenation with 100mol% conversion and 95.3% selectivity, applicable for the catalytic one-step hydrogenation of nitro-aromatic compounds. The reducibility of NiO species on different supports has been carefully studied. Some factors such as the type of carriers, the addition of modifiers, the silica source, the Ni loading, the H2 pressure and the reaction temperature and time play important roles in controlling the hydrogenation. In addition, the negative effect of the water amount has been observed. The recycling tests reveal the recyclability and stability of the supported Ni catalyst.

The 2014 Murray Raney Award Lecture: Architecture and Preparation of Supported Nickel Catalysts

The so-called method of sequential co-precipitation allows the production of Ni or Co catalysts varying in metal content, metal dispersion, structure and texture. In this method at first the metal is precipitated and subsequently the support precursor or “stabilizer”. Deposition–precipitation of base metals (Ni, Co, Cu) starting from metal ammine complexes yields highly dispersed metals, uniformly distributed across the carrier surface.

Oxidative-reforming of model biogas over NiO/Al2O3 catalysts: The influence of the variation of support synthesis conditions

In this study, nickel catalysts (20wt%) supported on γ-Al2O3 were prepared by the impregnation method. The γ-Al2O3, was synthesized by precipitation of bayerite gel obtained from aluminum scrap. The synthetic conditions of the bayerite gel varied as follows: precipitation pH ranging from 6 to 7; ageing temperature ranging from 25 to 80°C, the calcination temperature for all samples was 500°C. The catalysts and the supports were analyzed by temperature programmed reduction (H2-TPR), X-ray diffraction (XRD), physisorption of N2 (BET), X-ray absorption near-edge structure (XANES) and scanning electron microscopy (SEM). Isopropanol decomposition reactions over the catalysts were carried out to evaluate their acidity. SEM images of the spent catalysts showed that the morphology of the carbon formed during the reaction is of the filamentous type. The TPR analysis of the catalysts showed the presence of NiO species weakly interacted with the support as well as stoichiometric and non-stoichiometric nickel aluminate, the reduction of these species was also observed by XANES analysis. XRD analysis of the fresh catalyst showed peaks assigned to NiO, NiAl2O4 and γ-Al2O3. The best catalysts (samples NiAl7-25 and NiAl7-80) synthesized in this report showed high stability and high conversion values (CH4 (70%) and CO2 (78%)). These catalysts showed better performance than the catalyst supported on commercial γ-Al2O3, which showed a high coke formation which affected the course of the reaction. The γ-Al2O3 synthesized from bayerite obtained at neutral pH conditions was the best support for nickel catalysts in the oxidative-reforming of model biogas.

Nanoparticle Growth in Supported Nickel Catalysts during Methanation Reaction—Larger is Better

AbstractA major cause of supported metal catalyst deactivation is particle growth by Ostwald ripening. Nickel catalysts, used in the methanation reaction, may suffer greatly from this through the formation of [Ni(CO)4]. By analyzing catalysts with various particle sizes and spatial distributions, the interparticle distance was found to have little effect on the stability, because formation and decomposition of nickel carbonyl rather than diffusion was rate limiting. Small particles (3–4 nm) were found to grow very large (20–200 nm), involving local destruction of the support, which was detrimental to the catalyst stability. However, medium sized particles (8 nm) remained confined by the pores of the support displaying enhanced stability, and an activity 3 times higher than initially small particles after 150 h. Physical modeling suggests that the higher [Ni(CO)4] supersaturation in catalysts with smaller particles enabled them to overcome the mechanical resistance of the support. Understanding the interplay of particle size and support properties related to the stability of nanoparticles offers the prospect of novel strategies to develop more stable nanostructured materials, also for applications beyond catalysis.

Nanoparticle growth in supported nickel catalysts during methanation reaction--larger is better.

A major cause of supported metal catalyst deactivation is particle growth by Ostwald ripening. Nickel catalysts, used in the methanation reaction, may suffer greatly from this through the formation of [Ni(CO)4 ]. By analyzing catalysts with various particle sizes and spatial distributions, the interparticle distance was found to have little effect on the stability, because formation and decomposition of nickel carbonyl rather than diffusion was rate limiting. Small particles (3-4 nm) were found to grow very large (20-200 nm), involving local destruction of the support, which was detrimental to the catalyst stability. However, medium sized particles (8 nm) remained confined by the pores of the support displaying enhanced stability, and an activity 3 times higher than initially small particles after 150 h. Physical modeling suggests that the higher [Ni(CO)4 ] supersaturation in catalysts with smaller particles enabled them to overcome the mechanical resistance of the support. Understanding the interplay of particle size and support properties related to the stability of nanoparticles offers the prospect of novel strategies to develop more stable nanostructured materials, also for applications beyond catalysis.