Metal Oxide−Support Interactions in Fe/ZrO₂ Catalysts

Abstract

To reveal the metal oxide−support interactions in ZrO2-supported Fe oxide catalysts as a function of calcination temperature, 5 wt % Fe/ZrO2 was characterized by means of 57Fe Mössbauer spectroscopy, IR, XRD, and thermogravimetric analysis. The catalytic activity of Fe/ZrO2 was examined at 523 K for NO−CO reaction. It is shown that when Fe/ZrO2 is calcined below 573 K, small particles of hydrated Fe3+ oxyhydroxides (superparamagnetic at 297 K) are formed together with Fe3+ paramagnetic species ion-exchanged with the surface OH groups of ZrO2. In addition to the Fe3+ ion-exchanged species, Fe3+ oxide clusters and crystalline α-Fe2O3 particles are formed by successive dehydration of the oxyhydroxides on calcination at 973 K. When Fe/ZrO2 is calcined at 1073 or 1173 K, the Mössbauer spectroscopic results suggest the formation of Fe3+ cations trapped in surface vacant sites of ZrO2 at the expense of the Fe3+ oxide clusters. On the calcination at a higher temperature, crystalline α-Fe2O3 predominates with a small portion of the Fe3+ cations being in surface vacant sites. With 2 wt % Fe/ZrO2 prepared by a coprecipitation method and calcined at 1173−1373 K, Fe3+ cations dissolved in a ZrO2 lattice are formed in addition to a small amount of magnetically split component.

Effect of iron oxide loading on the phase transformation and physicochemical properties of nanosized mesoporous ZrO2

“…Okamoto et al [6] observed that Fe/ZrO 2 shows significantly weaker IR bands than ZrO 2 , indicating that the surface -OH groups are extensively consumed on the addition of 5 wt.% Fe. The authors also estimated the -OH group IR band intensities and approximately 65% of the -OH groups were lost for Fe/ZrO 2 sample.…”

“…Of these, tZrO 2 shows enhanced textural properties and lability and has oxygen atoms that can be readily exchanged; thus, this phase is suitable for numerous catalytic reactions [5]. In addition, the stabilization of t-ZrO 2 is considered the reason for the superiority of this catalyst for both activity and selectivity [6]. However, it should be noted that t-ZrO 2 is only stable at high temperatures (greater than 700 8C).…”

“…Boot et al [14] supported Fe oxides on ZrO 2 and suggested the formation of aFe 2 O 3 particles in a bimodal size distribution (7 nm and 12 nm), and they also studied the catalytic behavior of these catalysts for the dehydrogenation of butene. Okamoto et al [6] reported that at low Fe content (less than 5 wt.%), Fe/ZrO 2 catalysts exhibited a high catalytic activity in the NO-CO reaction. The same authors [ Despite a number of studies on the influence of Fe 2 O 3 on the stabilization of the ZrO 2 structure and its subsequent effect on catalytic performance in various reactions, an understanding of the differing interactions between Fe 2 O 3 and the surface of ZrO 2 at low calcination temperatures and high Fe loadings is considerably limited.…”

Incorporation of manganese and iron into the zirconia lattice in promoted sulfated zirconia catalysts

“…Impregnation of ZrO 2 with metal cation solutions followed by calcination produced supported α-Fe 2 O 3 46-49 with sometimes additional highly dispersed Fe 3+ species present, 48,49 or, accordingly supported α-Mn 2 O 3 . 50 Solid solutions may also form through solid state reaction between e.g.…”

Platinum- and iron-doubly promoted tungstated zirconia catalyst for n-butane isomerization reaction

“…On the other hand, Yamamoto et al [16] concluded that iron atoms form interstitial-type solid solution in the lattice of zirconia, that is, the atoms are located at the center of distorted oxygen octahedra. Okamoto et al [17] reported on a study of metal oxide-support interaction in Fe/ZrO 2 catalysts by Mossbauer spectroscopy. Quite recently, Carrier et al [18] has characterized the state of iron promoter in WZ catalysts and suggested that iron is occupying substitutional positions in the first surface layer of zirconia with a distorted octahedral coordination for Fe 3+ .…”