Surface properties and catalytic activity of ferrospinels of nickel, cobalt and copper, prepared by soft chemical methods

Abstract

Ferrospinels of nickel, cobalt and copper and their sulphatcd analogues were prepared by the room temperature coprecipitation route (0 yield samples with high surface areas. The intrinsic acidity among the ferrites was found to decrease in the order: cobalt> nickel> copper. Sulphation caused an increase in the number of weak and medium strong acid sites, whereas the strong acid sites were left unaffected. Electron donor studies revealed that copper ferrite has both the highest proportion of strong sites and the lowest proportion of weak basic sites. All the ferrite samples proved 10 be good catalysts for the bcnzoy lation of toluene with benzoyl chloride. copper and cobalt ferrites being much more active than niekel ferrite. The catalytic activity for benzoylation was not much influenced by sulphation, hut it increased remarkably with calcination temperature of the catalyst. Surface Lcwis acid sites, provided by the octahedral cations on the spinel surface. are suggested to be responsible for the catalytic activity for the benzoylation reaction.

The distinct effects of Mn substitution on the reactivity of magnetite in heterogeneous Fenton reaction and Pb(II) adsorption

“…The introduction of Co [13], Ti [19,20], V [18] and Cr [21] improves the Fenton catalytic activity of magnetite, while Ni shows an inhibitory effect [13]. Such distinct effects greatly depend on the oxidation states and occupancy of substituting cations [22,23]. Therefore, the experimental determination of cation distribution in the spinel structure and their oxidation states is an interesting challenge.…”

A comparative study about the effects of isomorphous substitution of transition metals (Ti, Cr, Mn, Co and Ni) on the UV/Fenton catalytic activity of magnetite

“…Ti 4+ [8], Cr 3+ [9], Mn 2+ [10], Co 2+ [11], and Ni 2+ [10]. Previous studies have investigated the effect of above substitutions on the heterogeneous Fenton catalytic activity of magnetite, which was greatly dependent on the occupancy, nature and amount of substituting metals [12][13][14]. For example, the catalytic activity relied on the octahedral cations rather than the tetrahedral ones, as the octahedral sites were almost exclusively exposed at the surface of inverse spinel structure [14].…”

“…Previous studies have investigated the effect of above substitutions on the heterogeneous Fenton catalytic activity of magnetite, which was greatly dependent on the occupancy, nature and amount of substituting metals [12][13][14]. For example, the catalytic activity relied on the octahedral cations rather than the tetrahedral ones, as the octahedral sites were almost exclusively exposed at the surface of inverse spinel structure [14]. Cr 3+ , Co 2+ and Mn 2+ obviously increased the • OH production for organic pollutant degradation by Fenton reaction, while Ni 2+ and Ti 4+ inhibited this process [8,10].…”

The contribution of vanadium and titanium on improving methylene blue decolorization through heterogeneous UV-Fenton reaction catalyzed by their co-doped magnetite

“…Mn 2+ /Mn 3+ and Co 2+ /Co 3+ ) can remarkably enhance the catalytic activity of magnetite in H 2 O 2 decomposition and organic oxidation [5,9]. The octahedral sites are almost exclusively exposed at the surface of the spinel crystallites and the catalytic activity is mainly due to octahedral cations [10]. Beyond all doubts, these experimental evidences are favorable for the application of metal-substituted magnetites in environmental engineering.…”

“…MB adsorption is closely related to the surface properties of the used adsorbent, including specific surface area, point of zero charge (PZC) and the amount of superficial hydroxyl [29][30][31]. The catalytic activity of metalsubstituted magnetite is mainly associated with the valence and occupancy of the doping metals [10]. Herein, complementary characterization technologies were utilized to investigate the influence of substituted cations on the above-mentioned properties, which is of high importance for well understanding the contribution and mechanism of V and Ti substitution on improving the adsorption and catalytic activity of magnetite.…”