Nickel Catalyst Precursors Research Articles

Effect of preparation method on the structure and catalytic property of activated carbon supported nickel oxide catalysts

A series of activated carbon (AC) supported nickel oxide (NiO) catalysts were prepared by aqueous reduction preparation methods with nickel nitrate as a precursor. The effects of preparation procedure and reducing agent on catalyst structure and catalytic property were investigated. Based on the information obtained from physico-chemical characterizations and sorbitol dehydration performances, preparation methods were found to have a significant influence on NiO distribution and surface acidity. The catalysts prepared through the simultaneous loading-reduction procedure had stronger acidity and higher NiO dispersion on the outer surface of AC, which contributed jointly to high sorbitol conversion (turn-over frequency of 190–240 h −1) and slightly low selectivity to anhydro sugar alcohols ( ca. 66%). Correspondingly, with the procedure of reduction of supported nickel catalyst precursors, the selectivity to anhydro sugar alcohols was improved by ca. 10%, while sorbitol conversion was quite low ( ca. 20%). Reducing agent exerted less influence on the structure compared with preparation procedure. However, when the simultaneous loading-reduction procedure was used, sodium borohydride influenced the acidity remarkably by formation of a new strong acid site, resulting in better dehydration performances.

The influence of halogen substituents at the ligand framework of (α-diimine)nickel(II) catalyst precursors on their behavior in ethylene oligomerization and polymerization

Abstract The ligand structure of (α-diimine)nickel(II) catalyst precursors has a significant influence on the behavior of these catalysts in the polymerization of ethylene. After activation with MAO, homogeneous nickel catalysts of this type are suitable to polymerize olefins to low molecular oligomers and/or more or less branched polymers. The variation of the ligand framework of the catalysts with halogen substituents in different positions shows clear dependencies between these substituents and the properties of the polymerization products. Unsaturated oligomers with an even number of carbon atoms (4–50) and all possible isomers as well as polymers up to a molecular weight of 36,000 g/mol can be obtained.

Selective two-phase catalytic ethylene dimerization by NiII complexes/AlEtCl2 dissolved in organoaluminate ionic liquids

Nickel(II) complexes dissolved in methyl-1-butyl-3-imidazolium chloride/AlCl3 molten salt in the presence of AlEtCl2 and aromatic solvents catalyse the dimerization of ethylene into butenes in a typical two-phase catalytic reaction. The nature of the nickel catalyst precursor has a strong influence on the reaction's activity and selectivity. Thus, ethylene dimers and trimers were obtained in the presence of NiF2 and NiCl2(PCy3)2, whereas only butenes were formed using the complex [Ni(MeCN)6] [BF4]2 as a catalyst precursor. In this latter case but-1-ene was formed with a selectivity of 83% and turnover frequencies of up to 1731 h-1. Moreover, the conversion and selectivity to but-1-ene increase with increasing ethylene pressure. The use of aromatic co-solvents is also essential for the ethylene dimerization, since other hydrocarbons induce the formation of higher ethylene oligomers. Copyright © 1996 Elsevier Science Ltd

TPR studies of the effects of preparation conditions on supported nickel catalysts

Temperature-programmed reduction (TPR) was used to characterize silica-supported nickel catalyst precursors with respect to the degree of interaction with the support and the metal oxide location by monitoring variations in the impregnation, drying and calcination stages of catalyst preparation. Three peaks at ~ 200, ~ 400 and ~ 500 °C were resolved in the TPR profile. The low temperature peak at ~200 °C was associated with the presence of Ni 3+ and had little influence on the subsequent reduction profile. The peak at ~400 °C was associated with the reduction of large nickel oxide crystallites in the small pores of the silica, with little or no interaction with the support. The peak at ~ 500 °C was associated with the reduction of small nickel oxide crystallites strongly attached to the support in the large pores of the silica. The TPR profile provides a useful ‘fingerprint’ for characterizing catalysts and for studying the effects of preparative variables on the final catalyst. The preparative stages which precede the drying stage (impregnation volume, time and successive impregnation) can be varied over wide limits without much effect, but those at and after this stage (drying, calcination, reduction) affect the TPR profiles and final catalyst performance markedly and require strict control, especially in industrial scale manufacture. The activity of the catalyst for cumene hydrogenolysis increases with the increasing proportion of the 500 °C TPR peak; this largely arises from the decrease in nickel crystallite size, which also accompanies an increase in the 500 °C peak.

Synthesis of heterogeneous olefin-oligomerization catalysts using homogeneous nickel-chelate complexes as a basis

The synthesis and characterization of two nickel(II) catalyst precursors are described. The first is derived from cross-linking of the bis(glycidyl ether) of bis(1- p-hydroxyphenyl-1,3-butanedionato)nickel(II) with 1,2-diaminoethane and the second is obtained from polystyrene-supported chloro-2,4-pentanedithionatotriphenylphosphine-nickel(II). The compounds and their homogeneous precursors have been examined for their activity in catalysing the oligomerization of 1-hexene using triethylaluminium and ethylaluminiumdichloride as co-catalysts. Results obtained indicate that the polymeric complexes are active when AlEtCl 2 is used as a co-catalyst, but not when AlEt 3 is used. Furthermore, oligomerization is accompanied by isomerization, while a high selectivity for dimers is observed. Analysis of the complexes after catalytic runs reveals that some leaching of the nickel ions from the polymers has taken place.