Tauster effect

The scope of the present paper is to emphasize that the interactions between support, metal and atmosphere are responsible for both the physical (size distribution, shape of the crystallites, wettability of the substrate by the crystallites and vice versa), the chemical and the catalytic (suppression of chemisorption, increased activity for methanation, etc.) manifestations of the supported metal catalysts. In the next section of the paper, a few experimental results concerning the behaviour of iron crystallites on alumina are presented to illustrate the role of the strong chemical interactions between the substrate and the compounds of the metal formed in the chemical atmosphere. Surface energetic considerations, similar to those already employed by the author (7,8), are then used to explain some of the observed phenomena. Subsequently, the Tauster effect is explained as a result of the migration, driven by strong interactions,... 

Arguments are provided below to emphasize that the Tauster effect is also a result of surface phenomena induced by strong interactions. 

The term SMSl was introduced by Tauster et al. (S.J. Tauster, S.C. Funk, R.L. Garten, J. Am. Chem. Soc. 1978, 100, 170) to denote the effect responsible for the drastic decrease in CO and H2 chemisorption on titania-supported metals after increasing the reduction temperature from 200 to 500°C. More details on this effect can be found in a review paper of Hadjiivanov and Klissurski (K.I. Hadjiivanov, D.G. Klissurski, Chem. Soc. Rev., 1996, 25, 61). 

One characteristic of the SMSI originally reported by Tauster et al. (13) was the restoration of normal chemisorption capacities on oxidation at 673 K followed by reduction at 473 K. Table I gives an example of this effect for the case of Rh/Ti02 catalysts (46). It is observed that the chemisorption capacity is partially restored when the oxidation treatment is carried out at room temperature. 

A vaguely defined metal-support interaction has frequently been used to describe modifications of metal properties observed when oxide-supported catalysts are thermally treated. After the original report by Tauster et al. (13) on the SMSI effect in Ti02-supported catalysts, the same authors (32) extended their operational definition to other reducible oxides. Consequently, several investigations were conducted using reducible oxide supports such as vanadia (87, 106, 154-156), niobia (157-162), or ceria (95). In general, the same characteristic features of Ti02 were obtained for these oxides, i.e., suppression in H2 and CO chemisorption capacity, suppression of catalytic activity for several reactions, promotion of the CO/H2 reaction, and reversibility by oxidation. 

Promotion of the Rates of C— O Bond Hydrogenation by the Oxide-Metal Interface CO hydrogenation catalysis has benefited greatly from the rediscovery of the unique catalytic behavior of oxide-metal interfaces first observed by Schwab [92]. The effect is commonly referred to as strong metal-support interaction, or SMSI (see also reference [93]). Tauster et al. [94, 95] reported large enhancement... 

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