Supported Nickel Catalysts Research Articles

The effect of hydrogen on thiophene catalytic removal over Ni/Al2O3

To investigate the essential role of H2 on thiophene removal over supported nickel catalysts, a NiO/Al2O3 catalyst was prepared, and a series of desulfurization reactions were carried out with different H2 feed concentrations. The characterization of fresh and spent catalysts indicated that reduced nickel (Ni0), which showed dependence on the H2 feed concentration, was the key factor to the thiophene reactive adsorption desulfurization (RADS) process. The equilibrium between sulfurization and reduction of nickel species retained the activity of the catalyst. The stability of the formed nickel sulfides was related to the H2 feed concentration. The higher H2 feed concentration favored the RADS process for the positive auto-regeneration of the nickel species.

Hydrogen production via steam reforming of ethylene glycol over Attapulgite supported nickel catalysts

Steam reforming of ethylene glycol was investigated over Ni-based catalysts supported on Attapulgite (ATP; originating from Jiangsu (JS), Anhui, and Gansu (GS) provinces in China). N2 adsorption–desorption, XRD, FTIR, H2-TPR, NH3-TPD, SEM, and TEM-EDS measurements were performed to analyze the catalyst properties. The results revealed that Ni/ATPGS had the largest particle size (17.9 nm) and the highest reductive degree (98.0%). Consequently, Ni/ATPGS showed the highest ethylene glycol conversion (97.2%) during the first 4 h of reaction. However, this catalyst showed the lowest H2 yield (71.2%), possibly owing to large Ni particle sizes as well as ample surface acidic sites and acidity, leading to a high selectivity toward CH4 (20.8%) and C2H4 (2.2%). In contrast, Ni/ATPJS presented the highest H2 yield (89.8%) owing to it having the smallest Ni particle sizes and lowest amount of surface acidic sites. Additionally, this catalyst showed the highest stability over 8 h of reaction. An examination of the spent catalysts revealed that Ni/ATPJS possessed excellent antisintering and coking properties.

An Effect of a Support Nature and Active Phase Morphology on Catalytic Properties of Ni-Containing Catalysts in Hydrogenation of Biphenyl

Ni/Sup catalysts were prepared, where SBA-15, γ-Al2O3, SiO2 were used as supports (Sup). The synthesized catalysts were investigated by the methods of low-temperature nitrogen adsorption, temperatureprogrammed reduction (TPR), and high-resolution transmission electron microscopy. The catalytic properties of the prepared catalysts were tested in liquid phase hydrogenation of biphenyl under conditions of a flow installation at temperatures of 60–100°C, pressure of 4 MPa, volumetric feed rate of 4–10 h–1 and H2: feed ratio of 1500 nM.. A 1 wt % solution of biphenyl in heptane,, as a model mixture, was used. It has been established that the activity of nickel hydrogenation catalysts depends on the nickel content and the type of support. The activity of supported nickel catalysts decreases in the series Ni-12/SBA-15 > Ni-12/SiO2 >> Ni-12/Al2O3. The kinetic characteristics of the biphenyl hydrogenation reaction were determined: the rate constants and activation energy for the hydrogenation of the first and second aromatic rings of the substrate molecule.

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

<p>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<sub>2</sub>O<sub>3</sub> 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 <em>n</em>-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.</p><p> </p>

Biofuel production from Nannochloropsis oculata microalgae in seawater without harvesting and dewatering over alumina-silicate supported nickel catalysts

The aim of this work was to study the production of biofuels from marine Nannochloropsis oculata without harvesting and dewatering over the single step sol-gel made alumina-silicate supported nickel catalysts at 80 °C and 1.0 atm. Sulfuric acid, hydrochloric acid, and nitric acid were used in the sol-gel to study the effect of acid type on catalyst activities. The catalyst made using sulfuric acid resulted in 74% microalgae conversion as compared to the catalysts made with other acids. Treatment of this catalyst with ~35 g of NaCl per kg of water at 80 °C and 1.0 atm for 24 h increased microalgae conversion to 91.5% under the same reaction condition and the bio-fuels ranging from mono/polysaccharides, polyols to esters and fatty acids were produced. This study showed that nickel and 25.1 μmol/g of total acidity and acidic strength having 130–380 °C of temperature range was necessary to achieve 91.5% conversion.

On the reactivity of carbon formed from CO CVD over Ni(1 1 1)/TiO2

The formation and reactivity of carbon on the supported nickel catalyst is a key issue for the low temperature activity and stability with methanation, reforming and other reactions. In this work, Ni(1 1 1)/TiO2 was prepared and applied as the catalyst to deposit carbon using low temperature chemical vapor deposition (CVD) of carbon monoxide. It was found that the CVD temperature could significantly affect the formation of carbon. With the CVD temperature decreasing, the disorder of the carbon increased, while the degree of graphitization was reduced. As a result, graphene-like films can be obtained at low CVD temperatures (from 300 to 350 °C). Such carbon films show a significantly improved reactivity with hydrogen and carbon dioxide. This explains the excellent low temperature activity and stability for CO2 or CO methanation over Ni catalysts with Ni(1 1 1).

Reversible Segregation of Ni in LaFe0.8Ni0.2O3±δ During Coke Removal

AbstractThe deactivation of supported nickel catalysts by coking is an important technological subject for many chemical processes, especially when high concentrations of unsaturated hydrocarbons are present in the feed gas. Here, the reversible segregation of Ni from a LaFeO3±δ perovskite‐type host lattice was exploited to completely recover a LaFe0.8Ni0.2O3±δ catalyst after it had been deliberately subjected to severe carbon deposition during CO2 methanation in ethylene rich feed gas for several hours. Temperature programmed reduction, X‐ray diffraction, electron microscopy, X‐ray absorption spectroscopy and catalytic activity tests were used to follow the catalyst structure along the various steps of reduction, reaction, coking and subsequent regeneration, while Raman spectroscopy and electron microscopy were used to characterize the nature of the carbon deposits. It is shown that upon reduction Ni atoms segregate to the surface of the perovskite to form catalytic active Ni particles. Oxidation stimulates Ni atoms to readopt the coordination environment of Fe in the perovskite matrix. This property persisted after severe catalyst deactivation by filamentous, partially graphitic carbon. It is demonstrated that simple catalyst reoxidation can be applied to oxidize all carbon deposits while additionally reverting segregated Ni back into the host lattice, thus protecting Ni from particle growth and resultant long‐term loss of catalyst activity over multiple regeneration cycles.

Supported nickel catalysts for anisole hydrodeoxygenation: Increase in the selectivity to cyclohexane

Abstract The hydrodeoxygenation (HDO) of anisole was performed with Ni catalysts supported on SBA-15 silica and protonated titanate nanotubes (PTN), in order to determine the effect of the support’s nature and the method of incorporation of Ni species on the catalytic activity and selectivity in HDO. Catalysts with 10 wt.% of Ni were prepared by two methods: deposition-precipitation with urea (DP) and the classical incipient wetness impregnation (IM). Characterization of the catalysts was performed by nitrogen physisorption, temperature programmed reduction, temperature programmed desorption of ammonia, high resolution transmission electron microscopy, scanning electron microscopy, powder X-ray diffraction, XPS and O2 chemisorption. The obtained results show that the support’s nature and the preparation method had a strong influence on the dispersion of the supported Ni species and their HDO performance. Catalysts with larger metallic Ni particles showed higher ability for hydrogenation of anisole and higher intrinsic activity (TOF) than those with smaller Ni particles. On the other side, the use of the PTN support and the DP with urea preparation method resulted in catalysts with increased acidity and improved selectivity for the formation of deoxygenated products (cyclohexane).

Catalytic hydrodeoxygenation of crude bio-oil in supercritical methanol using supported nickel catalysts

Pyrolysis oil (bio-oil) consists of high water content and vast variety of oxygenates (acids, alcohols, aldehydes, esters, ketones, sugars and phenols), causing some undesirable properties that prevent the direct use of bio-oil as a transportation fuel. Bio-oil upgrading to decrease its oxygen content provides a sustainable fuel that can be considered a valuable substitution for depleting fossil fuels. Catalytic hydrodeoxygenation (HDO) is an efficient method for bio-oil upgrading. This paper presents the HDO of crude bio-oil in supercritical fluid (ethanol, methanol, and 2-propanol) using a batch high pressure reactor. Supercritical fluids have unique physicochemical properties of liquid-like density and gas-like high diffusivity and low viscosity. The upgrading efficiency was evaluated by measuring the elemental composition (CHNSO), water content, carbon residue, and high heating value (HHV) of the bio-oil upgraded over Ni/HBeta catalyst. Compared to ethanol and 2-propanol, supercritical methanol resulted in a higher decrease in the oxygen content of bio-oil. The activity of Ni/HBeta was examined by varying the Ni loading (5–20 wt%), initial hydrogen pressure (10–30 bar), and reaction time (2–6 h). Meanwhile, effects of support materials (HZSM-5, HBeta, HY, Al-SBA-15, and silylated HBeta) on the performance of nickel catalyst in bio-oil upgrading were investigated using supercritical methanol.

An ordinary nickel catalyst becomes completely selective for partial hydrogenation of 1,3-butadiene when coated with tributyl(methyl)phosphonium methyl sulfate

Performance of an ordinary supported nickel catalyst was tuned to reach an almost complete selectivity for partial hydrogenation of 1,3-butadiene by coating it with a phosphonium-type ionic liquid (IL), tributyl(methyl)phosphonium methyl sulfate, [P4441][MeSO4]. Thanks to high chemical and thermal stability of [P4441][MeSO4], the reaction conditions could be pre-optimized for high partial hydrogenation performance before the deposition of the IL coating. When the catalyst was coated with IL, it provided a total butene selectivity of 99.5 ± 0.2%, a record high partial hydrogenation selectivity ever reported for a nickel-based catalyst. X-ray photoelectron spectroscopy results illustrated that the IL donates electrons to nickel sites and makes them selective for partial hydrogenation. The conductor like screening model for realistic solvents (COSMO-RS) calculations indicated that the IL coating also exerts a filter effect, which helps to maintain this high partial hydrogenation selectivity at all conversion levels.

Hydrodeoxygenation of pinyon-juniper catalytic pyrolysis oil using red mud-supported nickel catalysts

Red mud (RM) is an alkaline waste generated in the Bayer process of alumina production. In the present study red mud supported nickel catalysts (Ni/RM) were prepared at different concentrations of nickel (10, 20, 30, 40, 50, and 65 wt.%) and used to hydrodeoxygenate (HDO) pinyon-juniper (PJ) catalytic pyrolysis oil. Increasing the nickel content improved the activity of Ni/RM catalysts for HDO reactions. Maximum organic liquid yield (68.6%) was obtained when 40%Ni/RM was used. The upgraded oil had oxygen content of 1.35 wt.% and higher heating value of 45.77 MJ/kg compared to 24.88 wt.% and 28.41 MJ/kg, respectively, for the crude oil. For comparison, commercial Ni/SiO2-Al2O3 was also evaluated in HDO experiments. The HDO oil properties obtained using 40%Ni/RM at reaction temperature of 400 °C was similar to that of commercial Ni/SiO2-Al2O3 at reaction temperature of 450 °C. However, the organic liquid yield was much higher for 40%Ni/RM (68.6%) compared to the commercial Ni/SiO2-Al2O3 (41.8%). The commercial Ni/SiO2-Al2O3 produced more gas (27.6%) than the 40%Ni/RM (16.4%) and the coke yields for the commercial catalyst and Ni/RM catalyst were 7.3% and 4.2% respectively. Overall, application of Ni/RM improved HDO reactions and reduced cracking and coke formation compared to commercial Ni/SiO2-Al2O3.

Zeolite–supported nickel phyllosilicate catalyst for C[sbnd]O hydrogenolysis of cyclic ethers and polyols

In this study, a series of zeolites, including small pore (SAPO–34), medium pore (Ferrierite, ZSM–5, and ZSM–11), and large pore (MOR and BETA) zeolites were explored as supports for nickel catalysts. The catalysts were prepared by the deposition–precipitation (D–P) method to obtain ca. 10 wt% Ni loading. The structures of prepared catalysts were elucidated using a wide range of characterization techniques such as BET, XRD, TEM, H2–TPR, NH3–TPD, FTIR, and XPS. It was found that 1:1 nickel phyllosilicate structures is formed over D–P nickel catalysts, while 2:1 nickel phyllosilicate was identified only over Ni/BETA catalyst. Furthermore, Ni/ZSM–5 catalyst was also prepared by impregnation method as a reference to investigate the effect of preparation method. The impact of the topological structures of zeolite on the catalytic activity of reactants (i.e., cyclic ethers derived from furanic compounds), reaction intermediates (i.e., polyols) was subsequently investigated. The ring–opening of THFA can proceed over Ni/Ni phyllosilicate species on the external surface of the catalyst, producing pentane polyols. Then, the pentane polyol intermediates can further undergo ring–closure pathway, predominantly over the internal acid sites within zeolite structures (except for Ni/SAPO–34). It was found that medium–pore zeolites (ZSM–5 and ZSM–11) with mild acidity exhibit the highest reaction rate with a THP yield up to ca. 64%. Similarly, the highest catalytic activity during THPM conversion was achieved over ZSM–5– and ZSM–11– supported nickel catalysts, with up to 51% selectivity towards 16HDO. Comparing the zeolite maximum pore sizes and the kinetic diameters of the reactants and products with the catalytic performance, it is clear that topological structures of ZSM–5 and ZSM–11 have pore confinement effect on the reaction mechanism and catalytic activity in the hydrogenolysis of cyclic ethers and polyols.

Microcalorimetric adsorption and infrared spectroscopic studies of supported nickel catalysts for the hydrogenation of diisopropylimine to diisopropylamine

Diisopropylimine (DIPI) was used as a probe molecule to investigate the hydrogenation of CN on the Ni/Al2O3, Ni/LaAlO and Ni/LaOx catalysts. Microcalorimetric adsorption and infrared spectroscopy were applied to determine the surface bond strengths and structures of the reactant and product. It was found that the acidic support favored the adsorption and activation of DIPI and H2 on Ni, leading to the increased activity (TOF) for the hydrogenation of DIPI, while the basic support promoted the dehydrogenation of the amine product on Ni, being unfavorable for the hydrogenation of DIPI. In particular, the conversion of DIPI was significantly increased when isopropanol (IPA) was used as a solvent, due to the hydrogen transfer reaction (HTR) between IPA and DIPI, which was further evidenced by the infrared spectrum of co-adsorbed IPA and DIPI.

Influence of Cu and Mo components of γ-Al2O3 supported nickel catalysts on hydrodeoxygenation of fatty acid methyl esters to fuel-like hydrocarbons

In this work, series of Ni/γ-Al2O3 catalysts with or without Cu and Mo components were prepared, characterized and tested for the hydrodeoxygenation of fatty acid methyl esters (FAME) to hydrocarbons. The effects of Cu and Mo loading, impregnation sequence with sequential impregnation and co-impregnation involved and reaction conditions on catalytic performance were investigated. According to the TG data, the spent 20Ni-6Cu/γ-Al2O3 catalyst gives less weight loss than the spent 20Ni/γ-Al2O3 catalyst, which indicates that the addition of copper inhibits the carbon deposits behavior on catalyst surface during reaction. For 20Ni-6Cu/γ-Al2O3 and 20Ni-6Cu-nMo/γ-Al2O3 (n=2, 5, 8 and 12) catalysts, NH3-TPD analysis shows that the addition of molybdenum phase has significant impact on the acid sites of γ-Al2O3. When the loading of molybdenum is 5%, a new acid site is observed corresponding to the medium strength acid site. The Cu and Mo modified catalysts demonstrate better catalytic performance than Ni/γ-Al2O3 catalysts. Based on XPS results, Cu in the catalysts exists in the Cu2+ and Mo in the catalysts has two states: Mo4+ and Mo6+, and different impregnation sequences may influence the actual element composition of active phase on the surface of catalysts. In addition, the conversion of FAME and yield of alkane are related to the catalysts prepared with different impregnation sequence. Among all the catalysts, the trimetallic 20Ni-6Cu-5Mo/γ-Al2O3 prepared by sequential impregnation (the former Ni and Cu impregnation, the latter Mo impregnation) exhibits optimal catalytic performance. Under appropriate reaction conditions 350°C, 2.5 MPa, WSHV= 2.0 h−1, H2/oil ratio=1250 mL/mL, the conversion of FAME and yield of alkane are 98.4% and 94.2%.

COMBINED STEAM AND CO2 REFORMING OF CH4 OVER NICKEL CATALYSTS BASED ON Al2O3–MO (M= Mg, Ca, Ba)

A series of 10 wt% Ni/Al2O3–MO (M = Mg, Ca, Ba) catalyst was prepared by impregnation method for applying in the combined steam and carbon dioxide reforming of methane (CSCRM). In this study, five supported nickel catalysts were impregnated on different supports. All of the supports have been obtained by co–precipitation method and also have been investigated. Several techniques, including N2 physisorption measurements, X–ray powder diffraction (XRD), temperature–programmed reduction using H2 (H2–TPR), and transmission electron microscopy (TEM) were used to investigate catalysts’ physicochemical properties. The results showed that MgO was the most suitable promoter comparing with CaO and BaO in CSCRM. The presence of MgO in Ni/Al2O3 changed catalysts’ characteristics leading to an increase in the catalytic activity and stability with time on stream (TOS). It was found that the suitable catalyst was Ni–based on Al2O3–MgO of mass ratio 2:1 which showed a high metal dispersion as well as dominated spinel structure. The CH4 and CO2 conversion at 800 °C reached 99.8 % and 51.7 %, respectively. Catalytic stability of this catalyst with TOS at 800 °C could reach to more than 20 hours until it started decreasing.

Production of activated carbon as catalyst support by microwave pyrolysis of palm kernel shell: a comparative study of chemical versus physical activation

Palm kernel shell (PKS), representing an abundantly available oil palm waste in Malaysia, was transformed into activated carbon by microwave vacuum pyrolysis. PKS was first carbonized to produce biochar, followed by an activation process with chemical or water to produce chemically and physically activated carbon, respectively. The activated carbon materials were characterized for their porous characteristics and elemental and proximate composition to examine their suitability as catalyst support. Catalysts were synthesized by supporting nickel on the activated carbon materials and tested for their performance in the methane dry reforming reaction. Microwave vacuum pyrolysis of PKS-derived char resulted in up to 89 wt% yield of activated carbon. The activated carbon was detected to have high Brunauer–Emmett–Teller (BET) surface area associated with a highly porous surface, characteristics of high adsorption capacity corresponding to many sites for adsorption of metal atoms with great potential for use as catalyst support material. Nickel atoms were detected on the surface of the activated carbon catalyst support, indicating successful synthesis of nickel-supported catalyst. The catalysts showed high methane conversion (up to 43 %), producing approximately 22 % gaseous products (CO + H2). These results show that activated carbon produced from microwave pyrolysis of palm kernel shell is a promising catalyst support material. Chemically activated carbon performed better as catalyst support compared with physically activated carbon in terms of CH4 and CO2 conversions.

Synthesis of supported nickel catalysts in dynamic vacuum using nickel formate as precursor

The innovative method of synthesis of supported nickel catalysts from nickel formate as a precursor is proposed. The conditions of dynamic vacuum allow one to reduce the temperature of nickel formate decomposition, to minimize the agglomeration of metal particles, and to exclude the high-temperature stage of hydrogen reduction. The derived catalysts demonstrate high catalytic activity and are easily regenerated.

Effect of surface acidity/basicity on the selective hydrogenation of maleic anhydride to succinic anhydride over supported nickel catalysts

The catalysts 60%Ni/Al2O3, 60%Ni/MgAlO and 60%Ni/MgO were prepared and used for the hydrogenation of maleic anhydride (MA) to succinic anhydride (SA). Characterization results showed that Ni particles were highly dispersed in the catalysts so that they possessed the high density of active Ni sites, and thus the high activities for the reaction. In particular, it was found that the surface acidity favored the conversion of MA on Ni, but was unfavorable for the selectivity to SA, while the surface basicity played the opposite role. The Ni/MgAlO exhibited the proper acidity and basicity and thus the excellent performance for the reaction.

Investigation of nickel-impregnated zeolite catalysts for hydrogen/syngas production from the catalytic reforming of waste polyethylene

Catalytic steam reforming of waste high density polyethylene for the production of hydrogen/syngas has been investigated using different zeolite supported nickel catalysts in a two-stage pyrolysis-catalytic steam reforming reactor system. Experiments were conducted into the influence of the type of zeolite where Ni/ZSM5-30, Ni/β-zeolite-25 and the Ni/Y-zeolite-30 catalysts were compared in relation to hydrogen and syngas production. Results showed that the Ni/ZSM5-30 catalyst generated the maximum syngas production of 100.72 mmol g−1plastic, followed by the Ni/β-zeolite-25 and Ni/Y-zeolite-30 catalyst. In addition, the ZSM-5 supported nickel catalyst showed excellent coke resistance and thermal stability. It was found that the Y type zeolite supported nickel catalyst possessed narrower pores than the other catalysts, which in turn, promoted coke deactivation of the catalyst. Large amounts of filamentous carbons were observed on the surface of the Ni/Y-zeolite-30 catalyst from scanning electron microscope images. In addition, the influence of Si:Al molar ratio for the Ni/ZSM-5 catalysts in relation to hydrogen and syngas yield was investigated. The results indicated that hydrogen production was less affected by the Si:Al ratio than the type of zeolite support. Also, the Ni/ZSM5-30 catalyst was further investigated to determine the influence of different process parameters on hydrogen and syngas yield via different reforming temperatures (650, 750, 850 °C) and steam feeding rate (0, 3, 6 g h−1). It was found that increasing both the temperature and steam feeding rate favoured hydrogen production from the pyrolysis-catalytic reforming of waste polyethylene. The optimum catalytic performance in terms of syngas production was achieved when the steam feeding rate was 6 g h−1 and catalyst temperature was 850 °C in the presence of Ni/ZSM5-30 catalyst, with production of 66.09 mmol H2 g−1plastic and 34.63 mmol CO g−1plastic.

Catalytic cracking of biomass tar over char supported nickel catalyst

Catalytic cracking of biomass tar was investigated using steam gasification obtained char supported nickel catalyst in a lab-scale fixed bed reactor to determine the effects of catalytic cracking temperature, Ni loading and gas residence time on product distribution and gas composition. Results showed that the optimum catalytic cracking parameters were at 800 °C catalytic cracking temperature, 6 wt% Ni loading and 0.5 s gas residence time. The characterizations of tars were determined by ultimate analysis, FTIR and GC-MS. Compared with no catalyst cracking, the relative content of single-ring aromatics in tars obviously increases with the appreciably decreases in polycyclic aromatics, O-containing compounds and heterocyclic compounds after catalytic cracking, especially in Ni-6/char catalyst condition.The surface characteristics of Pre- and Post- char supported 6 wt% loading Ni catalysts were analyzed with BET, SEM, XRD and XPS. The BET and SEM results indicated that there was a slight deposition of coke on the surface of char after catalytic cracking. Meanwhile, XRD and XPS results indicated that NiO was transformed into Ni via carbothermal and hydrogenation reductions which contributed to the enhancement of tar conversion. These findings manifested that char supported nickel catalyst can be used as a low-cost catalyst to decompose tar.