Synthesis and characterisation of highly dispersed Ni/SiO2 catalysts prepared by gas-phase impregnation/decomposition (GPI/D) of a Ni(II) ?-diketonate precursor complex

Abstract

Silica-supported nickel catalysts have been prepared by a solventless technique involving the deposition of the [Ni(tmen)(acac) 2 ] precursor from the gas phase. According to UV-vis and IR spectroscopy and to elemental analysis, the initial deposition step results in the grafting of Ni(II) complexes on silanol groups to give predominantly [Ni(acac) 2 ( " Si-OH) 2 ] 0 monomeric inner-sphere complexes, with elimination of the neutral (tmen) ligands into the gas phase. Subsequent thermal treatments in oxidising atmospheres causes an oxidative decomposition of the (acac) ligands without nickel desorption or coalescence into oxide crystallites. The ensuing coordinatively unsaturated Ni(II) centres are reduced to Ni(0) by flowing hydrogen at low temperatures (300°C), yielding nanosized Ni particles as evidenced by TEM and O 2 titration. Thus, the gas-phase deposition technique represents an interesting alternative to conventional ''wet'' deposition procedures since it allows one to obtain well-dispersed supported nickel catalysts by reduction at low-temperatures.

Cobalt, nickel and ruthenium-silica based materials synthesized by the sol–gel method

“…The optical absorption band at 293 nm possibly is partially superimposed to the charge transfer band, which can be seen at higher energies, at 245 nm. A similar assignment was made by Stievano et al [17]. In this case the d-d absorption band in the 300-400 nm region, superimposed to the large tail of the charge transfer band of spectrum, determines the yellow color of adsorbed Ni complex.…”

“…8(c)), four absorption bands are present at 225, 306, 396 and 670 nm. The bands at 396 and 670 nm correspond to the spin-allowed transitions characteristic of Ni 2+ (d 8 ) in an octahedral field [17].…”

“…In this case the d-d absorption band in the 300-400 nm region, superimposed to the large tail of the charge transfer band of spectrum, determines the yellow color of adsorbed Ni complex. Rossman et al [18] associated this characteristic to the presence of a distorted octahedral coordination of the center solid Ni oxides solutions, such as MgSiO 3 :Ni [17]. However, for the NiSiO 2 non-calcined (Fig.…”

Synthesis of alumina supported nickel nanoparticle catalysts and evaluation of nickel metal dispersions by temperature programmed desorption

“…Several alternative approaches such as ion-exchange, deposition-precipitation of nickel-chelate complexes, citrate method, etc have been reported recently for the synthesis of highly dispersed nickel-based supported catalysts [11][12][13][14][15][16]. However, most of these studies have been devoted to the synthesis of Ni/ SiO 2 catalysts while the studies on the similar Ni/Al 2 O 3 system are scarce.…”

Chemisorbed nickel catalyst for the production of SWCNTs with a very narrow size distribution

“…Metal acetylacetonates can react with OH groups of the oxide surfaces . It is known that a subsequent thermal treatment causes decomposition of the metal complexes without metal desorption and with limited coalescence, yielding nano‐sized metal particles with a narrow size distribution . Promising results have been obtained by grafting cobalt acetylacetonate in a vapor phase, either on mesoporous silica or on silica powders .…”