Alumina-supported Nickel Catalysts Research Articles

Dry reforming of methane over Ni/Al2O3 catalysts: Support morphological effect on the coke resistance

Flower-like (Al2O3-F), wire-like (Al2O3-W) and sphere-like (Al2O3-S) alumina supported nickel catalysts (designated as Ni/Al2O3-F, Ni/Al2O3-W and Ni/Al2O3-S) were prepared for catalytic dry reforming of methane (DRM). The resultant catalysts exhibited variable catalytic activities and coke resistance performances in the reaction, which was closely dependent on their various physicochemical properties from the morphological effect of Al2O3 supports. To be precise, Ni/Al2O3-W presented adequately high catalytic activity and promising anti-coke behavior, which was attributed to its strong metal-support interaction, the surface dispersion of small-sized Ni nanoparticles and noticeable activation ability towards CO2. Ni/Al2O3-F possessed high anti-coke performance as well in terms of its significant CO2 activation ability. However, the encapsulation effect of Al2O3-F nanostructure resulted in insufficient abundance of metallic Ni active sites on the surface of Ni/Al2O3-F, thus giving rise to poor initial catalytic activity. The weak CO2 activation ability and the large particle size of metallic Ni on Ni/Al2O3-S induced the considerable formation of filamentous carbon after long-term DRM test. With regard to in situ DRIFTs analysis, the existence of OH* as the coke precursor scavenger and its reaction with the CHx* intermediate species from CH4 cracking were demonstrated to play crucial roles in dominating the overall anti-coke performances of Ni/Al2O3 catalysts. This work provides new insights into the development of high coke-resistance Ni-based catalysts from the perspective of support morphology modulation.

Neodymium promoted ceria and alumina supported nickel catalysts for CO2 methanation reaction

Two series of catalysts containing 20 wt.% nickel, promoted with different amounts of neodymium from 1 to 10 wt.% were prepared by the impregnation method, using nano-CeO2 and γ-Al2O3 as supports. Ceria supported nickel catalysts showed high activity in CO2 methanation reaction and weak activity changes were observed with an increase in Nd content. X-ray diffraction, hydrogen chemisorption and transmission electron microscopy studies evidenced a decrease in the average size of nickel crystallites and an increase in the active surface area of catalysts. The temperature-programmed reduction, oxidation and CO2 desorption, XPS, Raman and in-situ FTIR spectroscopy indicated complex changes in the nature of their redox and base centres. Non-promoted alumina supported nickel catalyst despite higher surface area showed lower activity than similar catalyst with ceria as support. However, an introduction of Nd-promoter led to strong increase in their activity. Such effect was mainly ascribed to the increase in their basicity, facilitation of CO2 activation and subsequent transformation of the intermediate surface species to methane with participation of hydrogen atoms activated on metallic nickel crystallites.

Highly Dispersed Nickel Nanoparticles on Hierarchically Ordered Macroporous Al2O3 and Its Catalytic Performance for Steam Reforming of 1-Methyl Naphthalene

In this study, we investigate the effect of a hierarchically ordered macroporous structure of alumina support on the steam reforming of 1-methyl naphthalene with mesoporous alumina-supported nickel and potassium (xK/Ni–MeAl), and macroporous alumina-supported nickel and potassium (xK/Ni–MaAl) catalysts. Hierarchically ordered macroporosity in Al2O3 supports plays an important role in maintaining the high Ni dispersion through multiple interactions in Ni–K over AlO4 tetrahedra in alumina. This, in turn, improves the catalytic performance of steam reforming, including high gas yields, turnover frequency for hydrogen production, and 1-methyl naphthalene conversion. At high K content, the Ni active sites over xK/Ni–MeAl catalysts significantly decrease, resulting in almost zero steam reforming rate in the reaction test. Conversely, the potassium–alumina interaction in xK/Ni–MaAl catalysts not only diminishes the formation of the inactive nickel aluminate phase but also maintains the highly dispersed Ni active sites, resulting in a high steam reforming rate.

Analysis by temperature-programmed reduction of the catalytic system Ni-Mo-Pd/Al2O3

Alumina-supported nickel catalysts are used to facilitate many reactions at various scales. However, the deactivation of these catalysts is an important problem that has prompted the search for solutions such as the addition of other metals that act as promoters. In this research, the interactions that form between the support and the metals have been studied, a fundamental property that directly affects the performance of the catalyst. With this idea, several Ni-Pd and Ni-Mo bimetallic and various Ni-Mo-Pd trimetallic samples have been prepared, and the reduction capacity of the oxide phases by temperatura-programmed reduction has been analyzed and studied. It has been found that in bimetallic catalysts, Pd favors the appearance of NiO species that are more easily reducible than Mo. In the same way, the data obtained from the trimetallic simples suggest that the impregnation order of Mo and Pd is not a determining factor in these catalysts. In addition, it has been found that the co-impregnation of Ni with Pd gives better results than the sequential impregnation of these metals. The results obtained have also shown that the order of nickel impregnation is decisive. In the case of Ni-Mo catalysts, by impregnating the molybdenum first, catalysts with better reducing properties can be obtained.

Controlling aging processes during bio-syngas methanation: SSITKA experiments over Ni/Al2O3 catalysts

A major barrier in the commercialization of biomass or waste gasification into bio-syngas is the presence of impurities such as NH3, HCl, tars and alkali in the products, being detrimental to downstream processes like the conversion of bio-syngas to substitute natural gas. The exact role and effects of these biomass-derived impurities on methanation catalysts are not clearly documented, especially when poisoning factors can combine with structural aging processes such as metal sintering under operating conditions. In order to unravel these aging phenomena under methanation conditions, the direct observation of Steady-State Isotopic Transient Kinetic Analysis curves semi-log transforms is combined with their modeling in view to evaluate the efficiency and sensitivity of this transient kinetic analysis. Thus, the toxicity of acetonitrile, trichloroethylene and toluene as representative of N-, Cl-, C- based poisons respectively, is shown to be strongly linked to the metal dispersion for the studied case of alumina supported nickel catalysts. A rationale linking such a transient kinetic analysis to methanation mechanisms is proposed in the present paper.

The Effects of Ce and W Promoters on the Performance of Alumina-Supported Nickel Catalysts in CO2 Methanation Reaction

The influence of Ce and W promoters on the performance of alumina-supported nickel catalysts in the CO2 methanation reaction was investigated. The catalysts were obtained by the co-impregnation method. Nitrogen low-temperature adsorption, temperature-programmed reduction, hydrogen desorption, transmission electron microscopy, X-ray diffraction, and photoelectron spectroscopy studies were used for catalyst characterization. An introduction of Ce and W promoters (1–5 wt %) led to the decrease in mean Ni crystallite size. Gradual increase in the active surface area was observed only for Ce-promoted catalysts. The increase in CO2 conversion in methanation reaction at low-reaction temperatures carried out over Ce-promoted catalysts was attributed to the increase in the active surface area and changes in the redox properties. The introduction of small amounts of tungsten led to an increase in the activity of catalysts, although a decrease in the active surface area was observed. Quasi in situ XPS studies revealed changes in the oxidation state of tungsten under CO2 methanation reaction conditions, indicating the participation of redox promoter changes in the course of surface reactions, leading to an improvement in the activity of the catalyst.

Biohydrogen production by glycerol Aqueous-Phase Reforming: Effect of promoters (Ce or Mg) in the NiAl2O4 spinel-derived catalysts

Biohydrogen production by Aqueous-Phase Reforming (APR) of glycerol was studied over nickel aluminate spinel-derived catalysts modified by Ce or Mg. As reference, an alumina supported nickel catalyst was also investigated. Catalysts were characterised by a sort of techniques in order to elucidate any structure-activity relationship, and tested for the WGS and CO hydrogenation reactions. It was concluded that the spinel catalyst allowed a better dispersion of the metallic Ni, and led to a more APR active and more hydrogen-selective catalyst. Mg and Ce doping further increased the nickel dispersion and increased basicity what could be related to their higher WGS relative reaction rate. Also, Mg doping hindered nickel reduction due to Ni-Mg interactions. Both promoters improved the stability of the textural properties under APR conditions, minimizing the formation of boehmite. Leaching of Ni was found, at lesser extent after Mg doping.

In Situ Hydrodeoxygenation of Guaiacol Using Magnetic Catalysts and Heterogeneous Hydrogen Producer

This research aims to figure out the effect of nickel, cobalt, iron powders and alumina-supported nickel catalyst on the hydrodeoxygenation (HDO) of guaiacol using zero-valent Zn as heterogenous hydrogen producer. The HDO tests are conducted at hydrothermal conditions in a batch micro reactor using equal amount of Zn and guaiacol feedstock, water to guaiacol ratio of 10, and catalyst load of 40 and 20 wt.% for metal powders and supported catalyst, respectively, with respect to the mass of guaiacol. Reaction time and temperature were set at 60 min and 300 oC. The fresh and exhausted supported catalysts were characterized by the XRD and SEM-EDX analyses. Among the tested commercial metal powders, Ni has the highest guaiacol conversion rate 51.3%, significantly higher than 11.8% of Fe and 20.0% of Co. Compared with metal powders, the alumina-supported nickel catalyst showed superior performance in terms of high conversion rate of 99.3% and high hydrodeoxygenation (HDO) and hydrodearomatization (HDA) efficiencies.

Direct Conversion of Carbon Dioxide to Methane over Ceria- and Alumina-Supported Nickel Catalysts for Biogas Valorization.

Direct methanation of CO2 over ceria- and alumina-supported nickel catalysts in the feed stream containing methane and traces of H2 S is reported. Stability tests for 20 h at 350 and 600 °C with a packed-bed reactor showed high resistance of the catalysts to sintering processes. Higher conversion at 350 °C was observed for ceria supported nickel catalyst. Thermodynamic analysis indicated that CO2 contained in biogas can be converted to methane without carbon formation under specific reaction conditions. An introduction of CH4 to CO2 -H2 feed stream led to the decrease in CO2 conversion and CH4 selectivity. An introduction of the trace amounts of H2 S into the feed stream led to the fast drop of CO2 conversion and CH4 selectivity; higher durability (20 %) was observed for Al2 O3 than CeO2 supported catalysts. An improved performance of catalysts coated onto high-pressure microchannel microreactors for the direct CO2 methanation reaction applying model biogas mixture was demonstrated.

Gas-Phase Hydrodechlorination of Chlorobenzene over Alumina-Supported Nickel Catalysts: Effect of Support Structure and Modification with Heteropoly Acid HSiW

The physicochemical and catalytic properties of 6%Ni/Al2O3 catalysts in the gas-phase hydrodechlorination of chlorobenzene (CB) are studied. The catalysts are synthesized by supporting nickel nitrate on two types of alumina—A (synthesized by aluminum isopropoxide hydrolysis) and E (manufactured by Engelhard)—with different morphologies and textures; some of the samples are unmodified, and some are modified by depositing 20% heteropoly acid (HPA) H8Si(W2O7)6 ⋅ nH2O. To prevent the HPA from decomposition, the air calcining and reduction of the modified materials are conducted at relatively low temperatures (250 and 330°C, respectively). To provide an adequate comparison, the catalysts containing no HPA are subjected to a similar treatment. Temperature-programmed reduction (TPR) reveals that air calcining at 250°C does not provide the complete conversion of the original nickel nitrate to oxide; nickel nitrates and hydroxynitrates are present in the catalyst precursors; their content decreases upon modification with the HPA. Differences in the composition and strength of Lewis acid sites on the surface of two types of Al2O3 lead to dissimilar coordination of nitrate and differences in nickel reducibility, as revealed by TPR, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy with CO adsorption, and in situ X-ray photoelectron spectroscopy (XPS). Nickel contained in Ni/Al2O3(E) undergoes reduction somewhat more readily than nickel in Ni/Al2O3(A) does; however, the conditions used in this study provide the reduction of only a small portion of nickel in the two catalysts. According to in situ XPS, TPR, and DRIFT spectroscopy with CO adsorption, the modification of Ni/Al2O3 with the HPA leads to a further change in the acidic properties and the coordination of nickel nitrate during impregnation and an increase in nickel reducibility; it prevents nickel from migration from the surface into the bulk of the sample and leads to the formation of new active sites owing to the strong nickel–tungsten interaction in the HPA. Depending on the nature of the support, modification with the HPA leads to an improvement (Ni/HPA/Al2O3(A)) or deterioration (Ni/HPA/Al2O3(E)) of the catalytic efficiency of the samples. At high temperatures, the benzene selectivity of the HPA-modified catalysts decreases owing to the formation of cyclohexane. The catalyst efficiency increases in the following order: Ni/HPA/Al2O3(E) < Ni/Al2O3(A) < Ni/Al2O3(E) < Ni/HPA/Al2O3(A). The most active catalyst—Ni/HPA/Al2O3(A)—exhibits the highest stability in long-term tests with an increase and subsequent decrease in temperature. The effect of nickel reducibility on the catalyst efficiency in CB hydrodechlorination is more significant than the effect of differences in texture and nickel content.

Unraveling the real active sites of an amorphous silica–alumina-supported nickel catalyst for highly efficient ethylene oligomerization

The Ni+ species in a heterogeneous N2-pretreated amorphous silica–alumina-supported nickel catalyst acted as the active sites for ethylene oligomerization.

Condensed Phase Guerbet Reactions of Ethanol/Isoamyl Alcohol Mixtures

The self-condensation and cross-condensation reactions of ethanol and isoamyl alcohol are examined to better understand the potential routes to value-added byproducts from fuel ethanol production. Reactions have been carried out in both batch autoclave and continuous condensed-phase reactors using a lanthanum-promoted, alumina-supported nickel catalyst at near-critical condensed phase conditions. Analysis of multiple candidate kinetic models led to a Langmuir–Hinshelwood rate expression that is first-order in alcohol with water as the strongly adsorbed species. This model provides the best fit of data from both batch and continuous reactor experiments. Activation energies for primary condensation reactions increase as carbon chain lengths increase. Selectivities to higher alcohols of 94% and 87% for ethanol and isoamyl alcohol, respectively, were observed at different operating conditions.

Catalytic performance of cubic ordered mesoporous alumina supported nickel catalysts in dry reforming of methane

In this research, a series of Ni-based catalysts with 10, 15, and 20% nickel content, supported on cubic ordered mesoporous alumina (COMA) for the first time were prepared employing one-pot synthesis and tested in dry reforming of methane reaction. In order to characterize the prepared samples N2 sorption isotherms, powder XRD, TEM, FT-IR, SEM/EDX, H2-TPR, XPS, TPO and TGA-DSC analyses were used. The 15%NiO/COMA catalyst showed the best catalytic performance over which conversions of CH4 = 99 and CO2 = 96% with H2/CO ratio = 0.89 at 850 °C were obtained. Performance stability test were carried out over catalyst of 15 wt% nickel content. Results were very promising as no activity loss was detected after 210 h of DRM reaction at 700 °C with GHSV = 18,000 ml/(g.h). TGA-DSC analysis proved that about 5 wt% carbon deposited onto the structure of endurance-tested catalyst after 210 h demonstrating excellent catalytic stability of COMA structure in DRM reaction.

Phosphorus-loaded alumina supported nickel catalysts for CO2 hydrogenation: Ni2P/Ni5P12 drives activity

A series of 5 wt% NiO-xP-Al2O3 with different phosphorus loading contents (x = 0, 5, 15 and 20 wt%) were prepared by a modified sol-gel method. A significant promotional effect of phosphorus on NiO-Al2O3 in CO2 hydrogenation is observed. All the catalysts reach the highest conversion at 600 °C with 61.54 %, 62.89 %, 63.88 % and 66.13 % respectively for 5 wt% NiO-Al2O3, 5 wt% NiO-5P-Al2O3, 5 wt% NiO-15P-Al2O3 and 5 wt% NiO-20P-Al2O3 catalysts. Ni/NiO/Ni2P/Ni5P12/AlPO4 interfacial species were detected on the surface as active species on the used catalysts by X-ray photoelectron spectroscopy. The formation ratio of the metal-phosphide is relatively low ∼3−5 %, and this atomic concentration is decreasing with the rising of the phosphate content. However, the nickel enrichment in the surface layer presumable in Ni2P/Ni5P12 form is very likely according to the P 2p spectra and the authors assume that could be responsible for the enhanced catalytic activity.

Catalytic reduction of nitrate in water over alumina-supported nickel catalyst toward purification of polluted groundwater

Pollution of groundwater with NO3– is a serious problem in the world. While catalytic reduction of NO3– over Pd-bimetallic catalysts including Cu-Pd and Sn-Pd is a promising method for purification of the groundwater, the use of precious metal is a major obstacle for practical applications. In the present study, we applied Ni/Al2O3 for the catalytic reduction of NO3– and compared the catalytic performance with that of unsupported Ni catalyst. The reaction rate over 5 wt.% Ni/Al2O3 was about 5 times higher than that of the unsupported Ni catalyst, based on unit weight of catalyst. While the unsupported Ni catalyst was completely deactivated in low partial pressure of H2 (=0.75 atm) and high concentration of NO3– (=800 ppm), Ni/Al2O3 was still active even under less reductive conditions ([NO3–]0 = 800 ppm and P(H2) =0.5 atm). The unsupported Ni catalyst had the Ni0 particles formed by the reduction of NiO with H2 at 310–420 °C. On the other hand, 5 wt.% Ni/Al2O3 possessed the Ni0 particles formed from NiAl2O4 on Al2O3 by the reduction with H2 above 450 °C. It is plausible that those Ni0 particles had different properties, giving different catalytic properties. The Ni loadings for Ni/Al2O3 had a significant impact on the catalytic properties. The reaction orders with respect to both NO3– and H2 were 0.8 for 5 wt.% Ni/Al2O3, while those were 0 and –0.2, respectively, for 10 wt.% Ni/Al2O3. On 10 wt.% Ni/Al2O3, there were two kinds of the Ni° particles, which were formed by low (310-420 °C) and high (above 450 °C) temperature H2 reductions. Unlike the Pd-bimetallic catalysts, the reduction of NO3– over Ni/Al2O3 did not proceed through NO2–.

Structure-sensitive hydro-conversion of oleic acid to aviation-fuel-range-alkanes over alumina-supported nickel catalyst

A highly active and stable γ-Al2O3-supported nickel nanoparticles catalyst (prepared by atomic layer deposition, ALD) was employed for the hydro-conversion of oleic acid to aviation-fuel-range-alkanes. The activity evaluation and characterization results suggested that this process is a structure-sensitive one for which step sites are more active than terrace sites. Ni(ALD)/Al2O3 catalyst enriched in Ni step sites thus presented high deoxygenation and hydrogenolysis activity. Additionally, Ni(ALD)/Al2O3 catalyst displayed high stability with only 6.5% drop in conversion after 10 h run owing to the development of strong metal-support interactions. After regeneration, the catalytic activity was recovered completely.

CO2 Methanation in the Presence of Ce-Promoted Alumina Supported Nickel Catalysts: H2S Deactivation Studies

The performance of alumina supported unpromoted and cerium promoted nickel catalysts in CO2 methanation reaction was investigated. It was found that the activity of catalysts in CO2 methanation reaction at low reaction temperatures can be improved by the increase in nickel loading and introduction of cerium promoter. The catalysts showed high resistance for sintering and coking at high reaction temperatures. A few stages of catalysts deactivation by H2S in the methanation reaction carried out at 475 °C with the time on stream were identified. It was found that an introduction of H2S to the stream (8 ppm) did not induce rapid decrease of activity. Slight and then strong drop of CO2 conversion and simultaneously the loss of methane selectivity was observed after specific time, depending on the catalysts composition. Deactivation of catalysts was related to the nickel content and the presence of cerium. X-ray diffraction studies indicated small changes of crystallite size with the time on stream. Raman spectroscopy studies pointed out that deactivation of catalysts was not connected with formation of carbon deposits. An in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy studies showed that exposition of catalysts to the reaction mixture containing the traces of H2S led to the blocking of nickel active sites responsible for CO2 and H2 activation and successive transformation to carbonyl and formate species.

Steam reforming of n-dodecane over mesoporous alumina supported nickel catalysts: Effects of metal-support interaction on nickel catalysts

Developing a highly active and stable Ni-based catalyst is still a challenge for the generation of on-site hydrogen through steam reforming of long-chained hydrocarbons, such as kerosene fuels. Ni nanoparticles (ca. 5 nm) on mesoporous alumina prepared by atomic layer deposition (ALD) were employed in steam reforming of n-dodecane, and exhibited a turnover frequency (TOF) of 477.6 h−1, whereas Ni nanoparticles on commercial alumina support prepared by impregnation method exhibited a TOF of 100 h−1. The high activity of ALD Ni catalysts was ascribed to high reduction degree, as confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), and H2-chemisorption. A deactivation was also observed on the ALD prepared catalysts, which was ascribed to the weak metal-support interaction, as confirmed by H2 temperature-programmed reduction (TPR). The ALD Ni/Al2O3 catalysts were further modified with CeO2 and they showed enhanced stability with 8% deactivation degree in steam reforming of n-dodecane. Further characterizations of spent catalysts showed that the presence of CeO2 was favorable for stabilizing Ni nanoparticles by enhancing moderate metal-support interaction, and reducing the formation of coke on the interfaces of NiCeO2.

Methane steam reforming at low temperature over Ni-MgO-Al2O3 catalysts: activity and resistance to coking

&lt;p&gt;The role of MgO as a factor improving the resistance to coking of the alumina supported nickel catalysts in the steam reforming of hydrocarbons is discussed. A series of catalysts containing variable amounts of MgO, NiO and a constant amount of Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; was prepared by the co-precipitation method. It was found that the specific activity of the catalysts exhibits a broad but not deep minimum for the MgO contents from 8.5 to 27.3 wt.%. At the same time these catalysts reveal a high resistance to coking either in the reaction with methane or with &lt;em&gt;n&lt;/em&gt;-butane. The most promising composition, in terms of the activity and simultaneous resistance to the coke formation, was found to be 27.3 wt.% of MgO and 39.0 wt.% of NiO. The analysis of various factors controlling the activity and resistance to coking leads to the conclusion that MgO reduces the catalysts acidity what, in consequence, reduces the rate of coke formation during the reforming reactions. Furthermore, The resistance to coking correlates well with the mean size of nickel crystallites, the same is observed for the specific catalyst activity.&lt;/p&gt;&lt;p&gt; &lt;/p&gt;

Steam reforming of toluene as model biomass tar to H2-rich syngas in a DBD plasma-catalytic system

Biomass tar is one of the most troublesome issues limiting the further development of biomass pyrolysis and gasification. In this study, a plasma enhanced catalytic steam reforming technology was applied for biomass tar removal. Toluene was selected as biomass tar surrogate. The nano-sized alumina-supported nickel and iron catalysts with different molar ratios of M/Al (M: Ni or Fe, 0:1, 1:3, 1:1, 3:1, 1:0) were prepared for catalytic steam reforming of toluene in a non-thermal plasma reactor featuring dielectric barrier discharge (DBD). The results showed that syngas was the dominant gas product of toluene decomposition. The conversion efficiency of toluene and energy efficiency using Ni-Al and Fe-Al catalysts both followed a sequence: M1Al3 > M1Al1 > M3Al1, which is in line with the BET surface area and pore volume. However, the selectivity of H2 and CO catalysed by Ni-Al and Fe-Al catalysts follows the order of M1Al3 < M1Al1 < M3Al1. Presumably, toluene dissociation is a process composed of adsorption-reaction-desorption. The formation of syngas is supposed to proceed as a series of ionic and free radical reactions occurring preferably in the gas phase. Ni1Al3 catalyst shows the largest potential in converting biomass tar into H2-rich syngas, with a maximum toluene conversion of 96% and a largest H2 yield of 2.18 mol/mol-toluene. Besides, the results showed that this hybrid plasma-catalysis system was potential in anti-carbon deposition.