Alumina‐supported nickel catalyst for liquid‐phase reactions: an expedient and efficient heterogeneous catalyst for hydrogenation reactions

The preparation of a new nickel(0)/Al₂O₃ catalyst for hydrogenation reactions is described. The nickel(0)/Al₂O₃ catalysts were prepared by impregnation of alumina with a solution of a nickel(II) salt. After drying, the nickel(II) salt was reduced under mild conditions into nickel(0) using t‐BuONa‐activated sodium hydride in tetrahydrofuran at 65 °C. The nickel(0)/Al₂O₃ catalysts obtained were characterized by transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. The supported catalysts were successfully used in solution‐phase hydrogenation of double and triple bonds. Although the activity of the nickel(0)/Al₂O₃ is comparable to non‐supported nickel(0) reagents, it has the advantage of being reusable more than ten times with only a slight decrease of reactivity. Copyright © 2003 John Wiley & Sons, Ltd.     

Efficient and Selective Formation of Unsaturated Carboxylic and Phenylacetic Acids from Diketene

A nickel catalyst promotes the multicomponent coupling reaction of diketene, an alkyne, and Me₂Zn to provide 3‐methylene‐4‐hexenoic acids in excellent yields. Under similar conditions, the combination of the nickel catalyst and Et₂Al(OEt) promotes a cycloaddition reaction involving dimerization of an alkyne to furnish phenylacetic acids. In the presence of PPh₃, a formal [2+2+1+1] cycloaddition reaction proceeds to afford regioisomeric phenylacetic acids via cleavage of the C?C bond.     

Cu(II)‐supported graphene quantum dots modified NiFe2O4: A green and efficient catalyst for the synthesis of 4H‐pyrimido[2,1‐b]benzothiazoles in water

NiFe₂O₄ nanoparticles are modified by graphene quantum dots (GQDs) and utilized to stabilize the Cu(II) nanoparticles as a novel magnetically retrievable catalytic system (Cu(II)/GQDs/NiFe₂O₄) for green formation of 4H‐pyrimido[2,1‐b]benzothiazoles. The prepared catalyst can be isolated assisted by an outer magnet and recovered for five courses without significant reduction in its efficiency. The as‐prepared magnetic heterogeneous nanocomposite was characterized by UV–Vis, FT‐IR, XRD, EDS, VSM, TEM, and ICP. Performing the reactions in environmentally friendly and affordable conditions (water), the low catalyst percentage, high yield of products, short reaction times, and easy workup are the merits of this protocol.     

Synthesis and characterization of bis[2-(1H-benzimidazol-2-yl)benzoato]nickel(II), and its use for preparation of dimethyl carbonate from methanol and CO2

A new complex, bis[2-(1H-benzimidazol-2-yl)benzoato]nickel(II) (NiL₂), has been synthesized and characterized. It was used as catalyst for synthesis of dimethyl carbonate (DMC) from methanol and CO₂ in the presence of dicyclohexyl carbodiimide (DCC) as promoter. The effects of temperature, reaction time, and amount of catalyst on the reaction, and the reusability of the catalyst, were investigated. A catalytic mechanism is proposed. The results revealed that NiL₂ + DCC had excellent catalytic activity, because this catalytic system promoted facile formation of DMC, with acceptable yield, in the presence of a small amount of NiL₂ and under moderate conditions (80 °C, 1.0 MPa). Moreover, the catalyst has been consecutively used five times without significant loss of activity.     

Preparation of Ni/poly(1,5-diaminonaphthalene)-modified carbon paste electrode; application in electrocatalytic oxidation of formaldehyde for fuel cells

This paper deals with electrochemical oxidation of formaldehyde in alkaline solution with a new electrocatalytic system composed of carbon paste electrode coated with poly(1,5-diaminonaphthalene) (P-1,5-DAN) film containing incorporated Ni(II)/Ni(III) redox ions. The modifier layer of (P-1,5-DAN-Ni)(OH)₂ at the electrode surface acts as a catalyst for the oxidation of formaldehyde in 0.1-M NaOH solution. Cyclic voltammetric and chronoamperometric experiments showed that the formaldehyde can be oxidized at the surface of Ni/P-1,5-DAN-modified carbon paste electrode. In cyclic voltammetry studies, the peak current of the oxidation of nickel hydroxide in the presence of formaldehyde increases and is followed by a decrease in the corresponding cathodic current. The rate constant (k) for the chemical reaction between the formaldehyde and nickel hydroxide has been evaluated by chronoamperometry method. This polymeric-modified electrode can oxidize the formaldehyde with high current density (over 7 mA cm⁻²). Thus, it can be a candidate as an anode for fuel cell applications.     

Practical Stannylation of Allyl Acetates Catalyzed by Nickel with Bu3SnOMe

A practical and scalable nickel‐catalyzed allylic stannylation of allyl acetates with Bu₃SnOMe is described. A variety of acyclic and cyclic allyl acetates, even with base‐sensitive moieties, undergoes the stannylation by using NiBr₂/4,4′‐di‐tert‐butylbipyridine (dtbpy)/Mn catalyst system to afford highly functionalized allyl stannanes with excellent regioselectivity and yields. Furthermore, the scope of protocol is also extended by the reaction of propargyl acetates, giving rise to propargyl or allenyl stannanes. Additionally, a unique diastereoselectivity using the nickel catalyst different from the palladium was demonstrated for the stannylation of cyclic allyl acetates. In the reaction, inexpensive and stable nickel complexes, abundant reductant (Mn), and atom‐economical stannyl source were used.     

Arylation catalytique d'organophosphorés. Produits de l'arylation,catalysée par les sels de nickel (II), de composés du phosphore tricoordiné.

Analysis of the products from the nickel (II) bromide catalysed arylation of tricoordinated phosphorus compounds R₂P-Z (Z  H, Cl, SR, NR₂ pointed out that this arylation always takes place on phosphorus resulting at first in formation of pseudophosphonium salts. Only the aminophosphonium salts are stable under reaction conditions; the other salts undergo several transformations which can be brought together in a general reactivity scheme to account for all the side products. On regard to other heteroatoms these results point out a particular ability of phosphorus to be arylated under nickel (II) catalysis.The reaction with secondary phosphines can be applied to synthetise diarylphosphonium salts.     

Steam-reforming of ethanol for hydrogen production

Production of hydrogen by steam-reforming of ethanol has been performed using different catalytic systems. The present review focuses on various catalyst systems used for this purpose. The activity of catalysts depends on several factors such as the nature of the active metal catalyst and the catalyst support, the precursor used, the method adopted for catalyst preparation, and the presence of promoters as well as reaction conditions like the water-to-ethanol molar ratio, temperature, and space velocity. Among the active metals used to date for hydrogen production from ethanol, promoted-Ni is found to be a suitable choice in terms of the activity of the resulting catalyst. Cu is the most commonly used promoter with nickel-based catalysts to overcome the inactivity of nickel in the water-gas shift reaction. γ-Al₂O₃ support has been preferred by many researchers because of its ability to withstand reaction conditions. However, γ-Al₂O₃, being acidic, possesses the disadvantage of favouring ethanol dehydration to ethylene which is considered to be a source of carbon deposit found on the catalyst. To overcome this difficulty and to obtain the long-term catalyst stability, basic oxide supports such as CeO₂, MgO, La₂O₃, etc. are mixed with alumina which neutralises the acidic sites. Most of the catalysts which can provide higher ethanol conversion and hydrogen selectivity were prepared by a combination of impregnation method and sol-gel method. High temperature and high water-to-ethanol molar ratio are two important factors in increasing the ethanol conversion and hydrogen selectivity, whereas an increase in pressure can adversely affect hydrogen production.     

Catalytic methanation reaction over supported nickel-rhodium oxide for purification of simulated natural gas

In this research,new catalyst with high industrial impact is developed,which can catalyze the conversion of CO2 to methane through methanation reaction.A series of catalysts based on nickel oxide were prepared using wetness impregnation technique and ageing,followed by calcination at 400℃.Rh/Ni(30:70)/Al2O3 catalyst was revealed as the most potential catalyst based on the results of catalytic activity measurement monitored by Fourier Transform Infrared Spectroscopy(FTIR)and Gas Chromatography(GC).The results showed 90.1%CO2 conversion and 70.8% yield at 400℃.     

Homo-Coupling of Terminal Alkynes Using a Simple,Cheap Ni(dppe)Cl2/Ag2O Catalyst System

A simple Ni(dppe)Cl₂/Ag₂O combination has been established as an efficient catalyst system for the homo-coupling of aromatic terminal alkynes. This reaction proceeds under mild conditions and can be applied to alkynone substrates. Various aromatic 1,3-diynes were obtained in good to excellent yields.     

Factorial design evaluation of the Suzuki cross-coupling reaction using a magnetically recoverable palladium catalyst

A magnetically recoverable catalyst [Fe₃O₄@SiO₂-AEAPTMS-Pd(II)] was prepared, fully characterized and had its catalytic activity evaluated on the Suzuki cross-coupling reaction under microwave irradiation. The reaction conditions for the synthesis of biaryl compounds was optimized in two stages - an initial fractional design 2⁴, in which the parameters reaction time, temperature, solvent and catalyst loading were evaluated, followed by a Doehlert design. The factorial design proved to be a viable approach for obtaining the optimal reaction conditions based on a relatively small number of experiments. Additionally, the biaryl derivatives synthesized by this method were obtained with good to excellent yields (71–96%) and the recovery and reuse of the palladium catalyst was also evaluated.     

Dehydrogenation of isopropanol on a cerium-nickel catalyst

The effect of a cerium additive on the catalytic activity of a 2 wt % Ni/SiO₂ catalyst is studied. It found that under both flow and static conditions the activity of (2 wt % Ni + 0.2 wt % Ce)/SiO₂ catalyst is higher than that of the original sample; the increase in activity results from a sharp increase in the number of active sites. A change in the composition of the surface layer of the catalysts is analyzed by X-ray photoelectron spectroscopy. It was found that the fraction of nickel decreases and the fraction of carbon increases in cerium-containing catalyst. An explanation of the change in the elemental composition of the catalytic active sites of a nickel catalyst in the presence of cerium is proposed on the basis of XPS data and previous quantum chemical calculations.     

Mild and efficient cyclization reaction of 2-ethynylaniline derivatives to indoles in aqueous medium

Results of the optimized cyclization reaction of 2-ethynylaniline derivatives to indoles catalyzed by copper(II) salts are described. The reactions can be carried out in a mixture of H₂O and MeOH in the presence of 1-ethylpiperidine at room temperature. These conditions can be applied to a bulky substrate, which is difficult to be cyclized efficiently by existing reaction conditions. Furthermore, this reaction condition was applied to a catalyst recycling reaction system.     

Propylene Dimerization by（η^5—C9H7）2 Nickel（Ⅱ）Catalytic System

The catalytic performance of Ni(η^5-Ind)2 complex in the dimerization of propylene was studied in combimation with an organoaluminum co-catalyst,eventually in the presence of a phosphine ligand.The effects of the type of aluminum co-catalyst and its relative amount,the nature of phosphine ligand and P/Ni ratio as well as the reaction temperature were examined.The results indicated that the nickel precatalyst exhibited high productivity for the propylene dimerization together with organoaluminum.It was likely to strongly modify the reactivity in the catalytic sytem when using phosphine ligand as additives,especially at the reaction temperature below 0℃.The catalytic system based on Ni(η^5-Ind)2 complex displaed an extremely high productivity(TOF up to 16900h^-1)and a good regioselectivity to 2,3-dimethylbutenes (2,3-DMB) in dimers(66.4%)under proper reaction parameters.     

A Noble‐Metal‐Free Nickel(II) Polypyridyl Catalyst for Visible‐Light‐Driven Hydrogen Production from Water

The complex [Ni(bpy)₃]²⁺ (bpy=2,2′‐bipyridine) is an active catalyst for visible‐light‐driven H₂ production from water when employed with [Ir(dfppy)₂(Hdcbpy)] [dfppy=2‐(3,4‐difluorophenyl)pyridine, Hdcbpy=4‐carboxy‐2,2′‐bipyridine‐4′‐carboxylate] as the photosensitizer and triethanolamine as the sacrificial electron donor. The highest turnover number of 520 with respect to the nickel(II) catalyst is obtained in a 8:2 acetonitrile/water solution at pH 9. The H₂‐evolution system is more stable after the addition of an extra free bpy ligand, owing to faster catalyst regeneration. The photocatalytic results demonstrate that the nickel(II) polypyridyl catalyst can act as a more effective catalyst than the commonly utilized [Co(bpy)₃]²⁺. This study may offer a new paradigm for constructing simple and noble‐metal‐free catalysts for photocatalytic hydrogen production.     

Palladium-catalyzed direct ortho-alkynylation of aryl acetamides with low catalyst loading

The palladium-catalyzed alkynylation of phenylacetic acid derivatives using 4-CF₃C₆F₄NH₂ as the auxiliary is described. The reaction efficiency can be greatly promoted by pyridine ligand, which enables the reaction to proceed at a catalyst loading as low as 1 mol%. Various functional groups are tolerated under the reaction conditions. The kinetic studies show that the rate of the reaction is first order in phenylacetamide and the Pd(OAc)₂ in combination of the pyridine ligand provides a highly robust and effective catalyst.     

Conversion of Methane into Methanol and Ethanol over Nickel Oxide on Ceria–Zirconia Catalysts in a Single Reactor

The conversion of methane into alcohols under moderate reaction conditions is a promising technology for converting stranded methane reserves into liquids that can be transported in pipelines and upgraded to value‐added chemicals. We demonstrate that a catalyst consisting of small nickel oxide clusters supported on ceria–zirconia (NiO/CZ) can convert methane to methanol and ethanol in a single, steady‐state process at 723 K using O₂ as an abundantly available oxidant. The presence of steam is required to obtain alcohols rather than CO₂ as the product of catalytic combustion. The unusual activity of this catalyst is attributed to the synergy between the small Lewis acidic NiO clusters and the redox‐active CZ support, which also stabilizes the small NiO clusters.     

Tethering of nickel(II) Schiff-base complex onto mesoporous silica: An efficient heterogeneous catalyst for epoxidation of olefins

A new hybrid catalyst has been prepared by tethering a nickel(II) Schiff-base complex via post-synthesis modification of mesoporous silica, MCM-41. The Schiff-base has been derived from salicylaldehyde and 3-aminopropyltriethoxysilane (3-APTES) which is chemically anchored on MCM-41 via silicon alkoxide route. The anchored Schiff-bases imposed a stable planar coordination geometry around the central nickel ions. The catalyst has been characterized by elemental analysis, FT-IR, UV-Vis, small angle X-ray diffraction (SAX) and transmission electron microscopy (TEM) studies. The SAX and TEM measurement showed the mesoporosity of the catalyst. The activity of the catalyst has been assessed in the epoxidation of olefins using tert-butyl-hydroperoxide (tert-BuOOH) as oxidant in heterogeneous condition. Immobilized nickel catalyst was found to be catalytically more active and selective compared to the similar type of nickel(II) complex as well as Ni(NO₃)₂·6H₂O in homogeneous media. The catalyst can be recycled and reused several times without significant loss of activity.     

Properties of anodic RuNiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>(OH)<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> catalysts synthesized on carbon supports with various dispersion degree

A number of catalysts of the (Ru-Ni)/C system is synthesized and studied for application in anodes of alkaline ethanol-air fuel cells. The carbon supports used are carbon blacks with different specific surface area and graphite powders. The X-ray photoelectron spectroscopy technique allowed detecting on the catalyst surface metallic ruthenium and nickel in the form of Ni(OH)2 hydroxide and possibly oxyhydroxide NiOOH. It is shown that the catalyst activity in the reaction of ethanol electrochemical oxidation grows at an increase in the specific surface area of the carbon support. The method of carbon monoxide oxidative desorption was used to determine the values of the specific surface area of the catalyst metallic phase. It is shown that at an increase in the relative ruthenium content from (1Ru3Ni)/C to Ru/C, the specific catalytic activity in the catalysts of the (Ru-Ni)/C system reaches the maximum value near the composition of (2Ru1Ni)/C. It is shown that the found optimum catalyst composition is independent of the carbon support dispersion degree. Activity in ethanol electrooxidation of the (2Ru1Ni)/C catalyst supported on the Ketjenblack EC-600 carbon black is 18 ± 3 A/g of the catalyst (>120 A/g of Ru) at 40°C and potential E = 0.5 V in the 2MKOH + 1 M C₂H₅OH electrolyte.     

Kinetic study of liquid-phase hydrodechlorination of hexachlorobenzene on Ni/C and 2%PdNi/C

Liquid-phase hydrodechlorination of hexachlorobenzene was kinetically studied in the presence of both nickel (Ni/C) and palladium-promoted nickel (2%PdNi/C) catalysts under different reaction conditions. Molecular hydrogen (at 1 and 20 atm) and sodium borohydride (NaBH₄) were used as reducing agents. In the presence of the nickel catalyst, the hydrodechlorination of C₆Cl₆ occurs via a consecutive mechanism (removal of one chlorine atom from the substrate at each stage), whereas with the 2%PdNi/C catalyst, the transformation of C₆Cl₆ occurs via both consecutive and multiplet mechanism (with the elimination of several chlorine atoms without desorption of the chloroaromatic substrate from the catalyst surface). The promotion of the nickel catalysts with palladium substantially changes the selectivity of formation of intermediate products of C₆C1₆ dechlorination. The mechanism of hydrodechlorination of hexachlorobenzene was suggested that explained the presence of only certain products of partial dechlorination of hexachlorobenzene in the reaction medium.