Alumina-supported Nickel Research Articles

Continuous flow hydrogenolysis of 5-hydroxymethylfurfural into 2,5-dimethylfuran over alumina-supported nickel–iron alloy catalysts

Continuous hydrogenolysis of 5-hydroxymethylfurfural to 2,5-dimethylfuran is successfully developed and demonstrated using alumina-supported nickel–iron alloy catalysts with in situ observation of the structural transformation.

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.

Chemoselective reduction of nitroaromatics using recyclable alumina-supported nickel nanoparticles in aqueous medium—exploration to one pot synthesis of benzimidazoles

An economical and eco-compatible synthetic protocol for chemoselective and regioselective reduction of nitroaromatics in water has been achieved using easily accessible alumina-supported nickel nanoparticles as a stable recyclable heterogeneous catalyst. Various sensitive substituents like allyloxy, benzyloxy, t-butyldimethylsilyloxy, hydroxymethyl, alkoxycarbonyl, formyl, keto, carboxylic acid, chloro, bromo, azo and cyano were tolerated in the aforesaid protocol. This method has been extended for the construction of imidazole derivatives through one-pot reductive condensation of 2-nitroaniline with diversely substituted benzaldehydes. Some of the synthesized imidazoles have been used as antibacterial, antiplatelet and antithrombotic agents.

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.

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.

Hydrothermal Sintering and Oxidation of an Alumina-Supported Nickel Methanation Catalyst Studied Using In Situ Magnetometry

The presented study investigated the effects of temperature (350–650 °C) and gas environment (pure Ar versus a H2O/H2 partial pressure ratio (PH2O/PH2) of 5) on the extent of sintering and oxidation of Al2O3-supported Ni0 nanoparticles (≈4 nm). We note that a PH2O/PH2 of 5 corresponds to a simulated CO conversion of 94% during methanation. Sintering and oxidation were studied using in situ magnetometry, while ex situ TEM analyses confirmed the particle sizes before and after the magnetometry-based experiments. It was found that increasing the temperature from 350 to 650 °C in Ar at atmospheric pressure causes a negligible change to the average size and degree of reduction (DOR) of the starting Ni0 nanoparticles. However, studying the same temperature window under hydrothermal conditions at 10 bar causes significant particle growth (≈9 nm) and the development of a bimodal distribution. Furthermore, the presence of steam decreases the DOR of Ni0 from 86.2% after initial activation to 22.2% due to oxidation. In summary, this study reports on the expected sintering and oxidation of Ni-based catalysts under high CO conversion conditions at elevated temperatures during methanation. Importantly, we were able to demonstrate how magnetometry-based analyses can provide similar size information (and changes thereof) as those observed with TEM but with the added advantage that this information can be obtained in situ.

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.

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.

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.

Phosphorus-tuned nickel as high coke-resistant catalyst with high reforming activity

Here we demonstrate that phosphorus (P) can affect both reforming and coking of alumina-supported nickel (10 wt% Ni with respect to alumina) at 750 °C and 1 atm. The P-containing catalysts were prepared by incipient wetness co-impregnation. Compared with the P-free nickel catalyst, the reforming activity is enhanced but the coke content decreases 8-fold at Ni:P atomic ratio of 4; the latter further reduces 55-fold at a ratio of 2, without a substantial decline in the reforming activity. Phosphorus not only improves nickel dispersion but also reduces the surface acidity and facilitates CO2 activation. At high P loadings, a portion of nickel transforms into nickel oxide during reforming. Besides tuning the reforming and coking activity, phosphorus changes the behavior of carbon crystallization. In methane pyrolysis and dry reforming, filamentous carbon occurs on the P-free catalyst but it is absent on the P-containing catalyst.

A Simple and Economical Route for the Synthesis of Alumina-Supported Metallic Nickel Nanoparticles

Abstract: The present work relates to the manufacture of the Ni/Al2O3 catalyst and is particularly directed towards the preparation of nano-metallic nickel supported on an alumina catalyst through a novel method that permits the nickel and alumina to be derived from aluminium and nickel nitrates as the source of aluminium and nickel particles. In a broad embodiment, this article relates to preparing Ni/Al2O3 nanoparticles using a glycine-assisted combustion method with simple and inexpensive procedures. In the present specification and appended claims of this invention, it avoids both nickel-metal oxidation and metal-support interaction yielding nickel aluminates as undesired materials. This is achieved by adjusting the ratio between fuel and oxidizers (F/O) at 2. The results revealed that the as-prepared catalysts consisted of Ni and Al2O3 with particle sizes ranging from 6-15 and 3-6 nm, respectively. The as-synthesized particles are regular in shape and have a porous and spongy network structure.

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–.

Hydrogenative Cross-Coupling of Nitriles with Amines on Alumina-Supported Nickel Nanoparticles

Key words nickel catalysis - hydrogenation - cross-coupling - nitriles - amines

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.

Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids

Reducing gaseous carbon dioxide to valuable chemicals and fuels by using gaseous hydrogen can decrease the concentration of greenhouse gases that contribute to global warming. Carbon dioxide conversion into fuels such as methane, methanol, and formic acid is a good hydrogen-storage method. In this paper, a comparative study of CO2 conversion into formic and acetic acids on alumina-supported nickel oxide with and without the presence of carbon is reported. NiO (111) with high surface area was synthesized through a simple and one-pot fusion solid-state method at 550 °C and 700 °C. The synthesized catalysts were tested in carbon dioxide hydrogenation reaction in a batch slurry reactor at 130 °C and under mild pressure. Interestingly, the optimum condition of the reaction also successfully produced C2 carboxylic acid in significant amounts. The highest levels of formic acid and acetic acid production were 8.13 and 7.63 mmol/L, respectively.

Support Effect on the Performance of Ni2P Catalysts in the Hydrodeoxygenation of Methyl Palmitate

The effect of support nature, SiO2 and γ-Al2O3, on physicochemical and catalytic properties of nickel phosphide catalysts in methyl palmitate hydrodeoxygenation (HDO) has been considered. Firstly, alumina-supported nickel phosphide catalysts prepared by temperature-programmed reduction method starting from different precursors (phosphate–Ni(NO3)2 and (NH4)2HPO4 or phosphite–Ni(OH)2 and H3PO3) were compared using elemental analysis, N2 physisorption, H2-TPR, XRD, TEM, NH3-TPD, 27Al and 31P MAS NMR techniques and catalytic experiments. The mixture of nickel phosphide phases was produced from phosphate precursor on alumina while using of phosphite precursor provides Ni2P formation with the higher activity in methyl palmitate HDO. Besides, the comparative study of the performances of Ni2P/SiO2 and Ni2P/Al2O3 catalysts demonstrates the apparent superiority of alumina-supported Ni2P in the methyl palmitate hydrodeoxygenation. Considering the tentative scheme of methyl palmitate transformation, we proposed that cooperation of Ni2P and acid sites on the surface of alumina provides the enhanced activity of alumina-supported Ni2P through the acceleration of acid-catalysed hydrolysis.

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.

Ni–Mo2C supported on alumina as a substitute for Ni–Mo reduced catalysts supported on alumina material for dry reforming of methane

Abstract In this study, alumina-supported Ni Mo catalysts were carburized to obtain alumina-supported nickel–molybdenum carbides as potential catalysts for dry reforming of methane. The typical carbide was compared with a low carburized material (in 5% H2/CH4) and a reduced Ni Mo catalyst. It was shown that the passivated alumina-supported Ni Mo catalysts by carbon lead to higher reactivity, selectivity, and stability for dry methane reforming reaction.