M. Houalla

Physico-chemical characterisation of impregnated and ion-exchanged silica-supported nickel oxide

X-ray analysis, reflectance spectroscopy, analytical electron microscopy and X.p.s. measurements have been used to investigate the influence of the preparation method on the dispersion and interaction of nickel oxide on silica. Two series of solids containing up to 10 wt % NiO were prepared, respectively, by pore volume impregnation and ion-exchange methods. It was found that impregnated samples are poorly dispersed and contain essentially bulk-like NiO crystallites or aggregates. Only in the sample with the lowest nickel content (2 wt % NiO) may the presence of a second nickel species be deduced. Conversely, ion-exchanged samples are well dispersed and give no evidence of the presence of NiO, but rather contain a surface layer of nickel hydrosilicate. The results were used to account for the dramatic difference in the reducibility of impregnated and ion-exchanged samples.

Joint Use of Xps and Diffuse Reflectance Spectroscopy for the Study of Cobalt Oxide Supported On Boron Modified Alumina

A study, by XPS and UV diffuse reflectance spectroscopy, of cobalt oxide supported on boron modified alumina indicates that boron addition strongly promotes the interaction of cobalt with the carrier. Co3O4 is predominant when cobalt is deposited on boron-free alumina, while only CoAl2O4 is detected on alumina containing 10 wt % B2O3.

Influence of the lithium content on the state, dispersion and reducibility of nickel oxide supported on γ-alumina

The influence of lithium on the dispersion, active phase-carrier interaction and reducibility of nickel oxide supported on alumina carriers has been investigated using X-ray diffraction analysis (X.r.d.), ultraviolet diffuse reflectance spectroscopy (d.r.s.), X-ray photoelectron spectroscopy (X.p.s.) and temperature programmed reduction (t.p.r.).On Li-free alumina, nickel is present in the form of a NiAl2O4 compound and dispersed NiO. Increasing the Li content leads to a decrease in the formation of NiAl2O4, due, presumably, to the concurrent formation of Li-containing spinel phases, and a concurrent increase in the reducibility of the nickel-containing phase.

The dispersion of nickel oxide supported on boron-modified silicas, as determined by TEM and XPS measurements

The dispersion of NiO supported on boron-modified silicas has been studied by transmission electron microscopy (TEM) and XPS. The TEM experiments showed that all NiO is present in the form of crystallites; values for the dispersion were calculated on the basis of measurements of the size distributions of these crystallites. The XPS measurements were interpreted using a model which assumes large particle sizes and no re-partitioning of the supported species between internal pores and the surface when boron-modification is performed. The variations of dispersion with boron content obtained from this model agree well with the variations measured by TEM.

Joint studies by X-ray photoelectron spectroscopy and analytical electron microscopy of the dispersion of nickel oxide supported on silica and silica–aluminas

The dispersion of nickel oxide, NiO, supported on a series of silica and silica–alumina carriers covering the range 100–0 % SiO2 has been investigated by photoelectron spectroscopy (X.p.s.) and analytical electron microscopy (a.e.m.). The results show that according to the nature of the support, two situations may arise: (1) With NiO on SiO2, the active phase is present as badly dispersed NiO aggregates. No surface compound or dispersed phase can be detected. (2) With NiO on SiO2–Al2O3, the supported phase exists in two forms: NiO aggregates and a dispersed phase. Increasing the Al2O3 content of the carrier leads to an increase in the concentration of the dispersed phase and a decrease in the average size of NiO aggregates.The results were interpreted on the basis of the interaction between the nickel salt precursor and the support during impregnation and heat treatment.

Tentative Classification of the Factors Influencing the Reduction Step in the Activation of Supported Catalysts

The communication is an attempt to classify the various parameters which affect the reduction step in the activation of supported oxides. Discussion will mainly be conducted with reference to hydrodesulfurization catalysts. The following groups of parameters will be discussed : dispersion, interaction between active oxides and support, reduction conditions, additives. Extensive reference will be made to mechanisms known in the field of the reaction of solids.

Joint use of X-ray photoelectron spectroscopy and analytical electron microscopy in the investigation of cobalt and nickel oxide supported on Na-doped alumina

The effect of sodium dope content on the repartition and degree of dispersion of alumina supported nickel and cobalt oxides has been studied by combined use of AEM and XPS. For both systems, increasing Na content brings about the segregation of the active species in the outer layers of the carrier particles. As to cobalt, one observes in addition the redispersion of Co in the form of cobalt aluminate, at the expense of the Co 3 O 4 crystallites.