Reduced Nickel Catalyst Research Articles

Effect of the preparation method on the hydrogenation activity of Ni/SBA-15 catalysts: Comparison of EDTA complexation and DPU

The SBA-15 material was synthesized and used as a support for nickel catalysts with 4 and 10wt.% metal loadings. Three preparation methods were used: a conventional incipient wetness impregnation with a nickel(II) nitrate solution (IM method), impregnation with a [Ni(EDTA)]2− complex solution (ED method) and deposition-precipitation with urea (DP method). The support and catalysts were characterized by N2 physisorption, X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy and temperature-programmed reduction. The reduced nickel catalysts were also characterized by high resolution transmission electron microscopy and powder XRD. Catalysts were evaluated in the hydrogenation of naphthalene in order to compare their catalytic performance (activity and selectivity). The obtained results show that the preparation method affected the dispersion and size distribution of nickel nanoparticles deposited on the SBA-15 surface as well as the degree of their reduction. ED and DP methods led to a better dispersion of Ni and higher hydrogenation activity in comparison with the conventional IM procedure. In addition, the catalysts’ selectivity to decalins and their ability to isomerize cis-decalin to trans-decalin were also affected by the preparation method used, increasing in the following order: XNS-IM < XNS-DP < XNS-ED for both Ni loadings (4 and 10wt.%). Therefore, the importance of the method used for the preparation of the Ni/SBA-15 catalysts was demonstrated.

ChemInform Abstract: Copper, Gold and Nickel Clusters with and without Metal—Metal Bonds in 50 Years of Fackler Group Chemistry

AbstractReview: 62 refs.

Porous nickel based catalysts for partial oxidation of methane to synthesis gas

The phase composition and texture of nickel catalysts supported on ribbon porous nickel with a magnesium oxide underlayer were investigated by X-ray diffraction, low-temperature nitrogen adsorption, and electron microscopy combined with energy dispersive X-ray microanalysis. The MgO underlayer was obtained by impregnation the porous nickel with a Mg(NO 3) 2 solution followed by calcination at 550 °C; nickel was supported additionally by impregnation with a Ni(NO 3) 2 solution followed by calcination at 450 °C. In the supported reduced nickel catalysts (800–900 °C, H 2) the phases of Ni and a solid solution of NiO in MgO were observed; a considerable part of nickel crystallites was epitaxially bound with MgO. The partial oxidation of methane to synthesis gas (800 °С, O 2/C = 0.65, GHSV = 127 L/g h) over porous nickel based catalysts was studied. The activity of initial nickel support decreased considerably during the partial oxidation of methane; the value of methane conversion decreased slightly after 100 h of testing on the supported nickel catalysts.

Enantio-Differentiating Hydrogenation of Methyl acetoacetate over Asymmetrically Modified Reduced Nickel Catalysts: The Effects of the Coverage of the Modifiers on the Enantio-Differentiating Ability

In order to investigate the factors for attaining a high enantio-differentiating ability (e.d.a.) for the enantio-differentiating hydrogenation of methyl acetoacetate over a tartaric acid pre-modified reduced nickel catalyst, the relation between the coverage of the modifiers on a nickel surface and e.d.a. was investigated. A Ni773 or Ni1373 (the reduced nickel catalyst prepared from a nickel oxide which was calcined at 773 K or 1,373 K, respectively) was used for the preparation of a modified catalyst. It was revealed that the tartaric acid coverage of about 0.2, the appropriate surface for the enantio-differentiation, such as the conditioned surface of Ni1373, and the inhibition of the hydrogenation on non-enantio differentiating sites by Br−, were all important for attaining a high e.d.a. This would be interpreted that only when tartaric acid is adsorbed as an isolated molecule on the appropriate surface, the acid exerts its intrinsic e.d.a.

Studies of co-modifier and carboxylic acid for the enantio-differentiating hydrogenation of 2-octanone over a tartaric acid in situ modified nickel catalyst

The effects of a co-modifier and carboxylic acid on the hydrogenation rate and the enantio-differentiating ability (e.d.a.) were studied for the hydrogenation of 2-octanone and methyl acetoacetate over a tartaric acid modified reduced nickel catalyst. For the hydrogenation of 2-octanone, tartaric acid, pivalic acid, and Na + were necessary for the appearance of the predominant e.d.a. Sodium pivalate, instead of the typical co-modifier, NaBr, was appropriate for the in situ modification of reduced nickel. The use of sodium pivalate resulted in a higher hydrogenation rate and e.d.a.

Hydrogen–deuterium exchange of methane on nickel surface prepared by the reduction of nickel oxide

The hydrogen–deuterium exchange reactions of methane in a deuterium stream were studied by a pulse experiment over a reduced nickel catalyst. The reduced nickel (Ni1373) prepared from nickel oxide calcined at 1373 K had a higher activity than the reduced nickel (Ni773) prepared from the nickel oxide calcined at 773 K. This could be due to the ratio of the Ni(1 0 0) to Ni(1 1 1). As the Ni1373 could have the surface of a higher Ni(1 0 0)/Ni(1 1 1) ratio, Ni1373 had a higher activity than Ni773.

Nickel Catalyst Stability toward Carboxylic Acids

Reduced (unsulfided) nickel catalysts can be used for hydroprocessing sulfur-free Fischer−Tropsch derived feed materials, but catalyst deactivation by metal leaching can be a problem in the presence of carboxylic acids. Leaching of reduced nickel catalysts by carboxylic acids takes place by the formation of nickel carboxylates. Carboxylic acid leaching of nickel can be prevented by operating above the carboxylate decomposition temperature, which was found to be in the range 280−305 °C for the C2−C5 nickel carboxylates. Unfortunately this is not industrially practical, because of the hydrogenolysis propensity of reduced nickel catalysts at these conditions. It was also found that nickel leaching did not monotonically increase with temperature, but was inhibited at >200 °C, probably due to polymerization of the nickel carboxylates.

The Durability of the Enantio-Differentiating Ability of a Tartaric Acid–NaBr-Modified Reduced Nickel Catalyst Pre-Modified in Tetrahydrofuran

The enantio-differentiating hydrogenation of methyl acetoacetate was carried out over a (R,R)-tartaric acid–NaBr-modified reduced Ni catalyst. The reduced Ni was pre-modified in a tetrahydrofuran solution of tartaric acid and NaBr at atmospheric pressure or at a high hydrogen pressure. The enantio-differentiating ability of 70–90% was maintained during 40 runs over the reduced nickel catalyst pre-modified at 9 MPa hydrogen and 373 K. The results indicated that the durability of a high enantio-differentiating ability of an in-situ-modified catalyst would be attributed to the modification conditions at the high hydrogen pressure of 9 MPa and the high temperature of 373 K in the autoclave.

Enantio-differentiating hydrogenation of methyl acetoacetate over reduced nickel catalysts pre-modified in methanol

The enantio-differentiating hydrogenation of methyl acetoacetate was carried out over a (R,R)-tartaric acid-NaBr-modified reduced Ni catalyst. Reduced Ni was pre-modified in a methanol solution of tartaric acid and NaBr. It was revealed that the pre-treatment of methanol by molecular sieves was essential for attaining the high enantio-differentiating ability of 80–90% and high durability during repeated uses of the recovered catalyst.

Decomposition of methane with an autocatalytically reduced nickel catalyst

Thermal decomposition of nickel acetate ( T > 300 °C ) dispersed on either silica or cordierite supports resulted in a mixture of Ni 0/NiO that was catalytically active for the decomposition of methane to produce CO-free hydrogen, without the need for any pretreatment (i.e., using H 2 at high temperature (>500 °C) for at least 2 h). The carbon yield (g C/g Ni) for the catalysts supported on SiO 2 ( ∼ 200 – 300 m 2 /g) increased with an increase in the catalyst NiO mean crystallite size. XRD and FE-SEM studies confirmed the formation of graphitic-type carbon filaments during the methane decomposition.

Study of the properties of nickel oxide and nickel as precursors for the tartaric acid-NaBr-modified nickel catalyst

Nickel oxide was prepared by the decomposition of nickel hydroxide and then the nickel oxide was reduced to form the nickel catalyst. The properties of the nickel oxide and the reduced nickel were studied in relation to the enantio-differentiating ability (e.d.a.) of a tartaric acid-NaBr-modified reduced nickel catalyst. The modified nickel catalyst prepared from nickel oxide with less non-stoichiometric oxygen produced a high e.d.a. for the hydrogenation of methyl acetoacetate. The high crystallinity of the nickel oxide and the resultant nickel would be required to attain a high e.d.a.

Repeated use of the in-situ modified nickel catalyst for the enantio-differentiating hydrogenation of 2-octanone

Repeated use of the in-situ modified reduced nickel catalyst prepared from nickel oxide was carried out for the enantio-differentiating hydrogenation of 2-octanone. The tartaric acid (TA)–NaBr in-situ modified reduced Ni retained over 60% of the enantio-differentiating ability (eda) of the catalyst in the hydrogenation at 373 K for repeated 16 runs by the addition of tartaric acid and sodium 2-ethylhexanoate to the reaction media before every other run. The quantitative analyses of the adsorbed species on the catalyst surface revealed that the tartaric acid and sodium ions adsorbed in the 1st run were gradually desorbed during the repeated runs. The result supports the necessity of the addition of tartaric acid and sodium 2-ethylhexanoate to the reaction media every other run for retaining the enantio-differentiating ability.

Enantio-differentiating hydrogenation of methyl acetoacetate over asymmetrically modified reduced nickel catalysts The effects of the nickel sources on the enantio-differentiating ability

Abstract The enantio-differentiating hydrogenation of methyl acetoacetate was carried out over a tartaric acid–NaBr-modified reduced nickel catalyst. Nickel hydroxide and nickel carbonate were used as the precursors of the nickel oxide. They were calcined to nickel oxides, then reduced to nickel metal (reduced nickel catalyst). It was revealed that the calcination temperature of the precursors was an important variable for attaining the high enantio-differentiating ability (e.d.a.) of the catalyst. The nickel surface with the least lattice defects would be appropriate for attaining a high e.d.a.

Study of the parameters controlling the enantio-differentiating ability of asymmetrically modified solid catalysts for the hydrogenation of γ-ketoesters

The enantio-differentiating hydrogenation of γ-ketoesters was carried out over asymmetrically modified solid catalysts. The parameters affecting the enantiomer excess (ee) were investigated and the results were compared with those of the hydrogenation of methyl acetoacetate and 2-octanone reported in the literature. The highest value of enantiomer excess of 51% was attained for the hydrogenation of methyl 4-oxopentanoate over a tartaric acid (TA)-NaBr-modified reduced nickel catalyst prepared from nickel oxide. The amount of NaBr in the modification solution needed to be optimized according to the manufacturers of the nickel oxides. The addition of an appropriate amount of carboxylic acid to the reaction media increased the enantiomer excess of the hydrogenated products.

Enantio-Differentiating Hydrogenation of 2-Octanone over Modified Nickel Catalysts Prepared by an In Situ Modification

Abstract The enantio-differentiating hydrogenation of 2-octanone was carried out over a tartaric acid-modified reduced nickel catalyst. It was shown that the in situ modification of the Ni surface was available for the hydrogenation of 2-octanone in the presence of a large amount of pivalic acid in the reaction media. An optical yield of 74% was attained with the in situ modified reduced Ni catalyst.

A study on the ignition process for the catalytic partial oxidation of methane to synthesis gas by MS-TPSR technique

The ignition processes for the catalytic partial oxidation of methane (POM) to synthesis gas over oxidic nickel catalyst (NiO/Al2O3), reduced nickel catalyst (Ni0/Al2O3), and Pt-promoted oxidic nickel catalyst (Pt–NiO/Al2O3) were studied by the temperature-programmed surface reaction (TPSR) technique. The complete oxidation of methane usually took place on the NiO catalyst during the CH4/O2 reaction, even with a pre-reduced nickel catalyst, and Ni0 is inevitably first oxidized to NiO if the temperature is below the ignition temperature. It is above a certain temperature that Ni0 is formed again, which leads to the start of the POM. The POM can be initiated at a much lower temperature on a Pt–NiO catalyst because of Pt promotion of the reduction of NiO. The POM in a fluidized bed can be easily initiated due to the addition of Pt.

Mechanism for catalytic partial oxidation of methane to syngas over a Ni/Al 2O 3 catalyst

The mechanism of catalytic partial oxidation of methane to syngas (POM) over a Ni/α-A1 2O 3 catalyst was studied by using a pulse reactor and temperature-programmed surface reaction (TPSR) techniques. Over a reduced nickel catalyst (Ni 0/A1 2O 3), methane activation follows the dissociation mechanism; while on oxidic nickel catalysts (NiO/Al 2O 3), methane is first oxidized to carbon dioxide and water, and simultaneously, NiO is reduced to Ni 0. CH 4 dissociation occurs over Ni 0 active sites, generating hydrogen and surface C species. A transient process was observed during the CH 4/O 2 reaction. The nickel valence was transformed from NiO to Ni 0 at a certain critical temperature and simultaneously, the reaction was transformed rapidly from the complete oxidation of methane to the partial oxidation of methane. It has been found that the POM reaction takes place over a thin layer of the catalyst bed. This reaction zone is nearly isothermal, over which almost 100% of oxygen and more than 90% of methane are converted. The temperature drop in the downstream of the catalyst bed does not imply that the steam or carbon dioxide reforming reaction occurs in the lower part of the bed. Ni 0 species constitute the active sites for the partial oxidation of methane to syngas. Both methane and oxygen are activated on Ni 0 sites, generating surface Ni⋯C and Ni δ+ ⋯O δ− species. These two kinds of intermediates have been proposed to account for the mechanism of methane partial oxidation. The Ni δ+ ⋯O δ− species over Ni 0 catalyst surface is considered to be a kind of weakly bounded, mobile oxygen species. The reaction between Ni δ+ ⋯O δ− and Ni⋯C intermediates generate the primary product of CO. However, the presence of NiO over the catalyst surface significantly reduces the CO selectivity. Thus, the NiO species are not possible to be the intermediate for the POM reaction. The mechanism of partial oxidation of methane should follow the direct oxidation route.

99/03673 Hydrogen production from cellulose using a reduced nickel catalyst: Minowa, T. and Ogi, T. Catal. Today, 1998, 45, (1–4), 411–416

99/03673 Hydrogen production from cellulose using a reduced nickel catalyst: Minowa, T. and Ogi, T. Catal. Today, 1998, 45, (1–4), 411–416

99/01169 Hydrogen production from cellulose in hot compressed water using reduced nickel catalyst: product distribution at different reaction temperatures : Minowa, T. and Fang, Z. J. Chem. Eng. Jpn., 1998, 31, (3), 488–491

99/01169 Hydrogen production from cellulose in hot compressed water using reduced nickel catalyst: product distribution at different reaction temperatures : Minowa, T. and Fang, Z. J. Chem. Eng. Jpn., 1998, 31, (3), 488–491

Hydrogen production from biomass by catalytic gasification in hot compressed water

Cellulose, a major component of woody biomass, was gasified to hydrogen rich gas using a reduced nickel catalyst in hot-compressed water of around 350 °C and 18 MPa. During the gasification, steam reforming and methanation can occur, and the methanation was prevented at subcritical condition. The reaction model and the catalyst are described.