Interplay of anions and ligands on the nature and reducibility of NiOx/Al2O3 catalysts prepared by impregnation

Abstract

When NiOx/Al2O3 catalysts (Ni wt% = 1.5) are prepared by impregnation using [NiL2(H2O)2]X2 as precursors (L = diamine, X = Cl- or NO3-), a supported oxidic or metallic phase can be selectively obtained after thermal treatment in N2 depending on the nature of the ligand and counter anion; the oxidic phase can be reduced at a lower temperature than the classical nickel aluminate phase obtained from [Ni-(H2O)6](NO3)2.

Amorphous Silica as a Versatile Supermolecular Ligand for NiII Amine Complexes: Toward Interfacial Molecular Recognition

“…[50,52,53] Supramolecular adducts involving this pattern have been found in situations reminiscent of our case, for instance, between the aqua ligands of the complex [Ni(H 2 O) 6 ] 2 + and oxygen atoms of crown ethers. [54] Similar bonds were recently evidenced spectroscopically in a study on the interaction of [Ni(en) 2 (H 2 O) 2 ] 2 + with an alumina surface, [55] and cooperative effects quite similar to our model were proposed by Taylor et al for the adsorption of cobalt neocuproine complexes on silica. [56] The next step would be to identify the nature of the surface oxygen atoms that act as hydrogen-bond acceptors.…”

Monitoring Transport Phenomena of Paramagnetic Metal‐Ion Complexes Inside Catalyst Bodies with Magnetic Resonance Imaging

“…Besides metal precursor salts, organic complexing agents such as citric acid and nitrilotriacetic acid are often added to impregnation solutions. [9][10][11] Different metal chelate complexes can thus be formed in the impregnation solution depending on pH and concentration. Moreover, it has been shown that pH gradients can occur inside catalyst bodies after impregnation, which can be expected to influence the interaction between metal-ion complexes and the support surface.…”

From Al2O3-supported Ni(II)-ethylenediamine Complexes to CO Hydrogenation Catalysts: Importance of the Hydrogen Post-treatment Evidenced by XPS

“…Subsequent treatments are detailed in Sect. 3 6 ](NO 3 ) 2 following the procedure described in [6].…”

“…Another route consists in changing the nickel precursor to salts containing nitrates and ligands such as ethylenediamine (en, NH 2 -CH 2 -CH 2 -NH 2 ), and decomposing them in argon [3,6,7]. During heating, nitrates oxidize the en ligands but not completely.…”

“…However, dispersed particles of metallic nickel (a few nm) are difficult to obtain by this method for two reasons: upon thermal activation, a fraction of nickel ions migrates into alumina to form an ''aluminate'' phase which cannot be reduced by hydrogen below 900°C [1,2]; when reduced at such temperatures, metallic nickel sinters and forms particles larger than 10 nm, with an associated low exposed metallic surface area [3]. Direct reduction in hydrogen of supported nickel nitrate has been reported to circumvent these problems, but metal sintering may nevertheless occur because of the exothermicity of nitrates reduction [4] and the absence of aluminate is not guaranteed [5].…”