Strong-metal-support-interaction

These results are a small fraction of the published data concerning metal-support interactions. While, as discussed later, there are some logical conclusions that can be drawn concerning the nature of the strong metal-support interactions there are too many factors involved to be able to sort through the mass of data concerned with the interaction of non-reducible or non-reduced supports and the metal particles on them. 

One obvious problem concerns the comparison of catalysts having varying dispersions or metal particle sizes since, as discussed above, the MSI are particle size dependent. Less obvious factors are the metal precursor salts and the methods used to prepare the catalysts. It is known that trace amounts of some of the ions that may be present in the catalyst preparation can influence catalyst activity. Such ions may or may not be present in the metal salts used to prepare the catalyst and the amount of such material left on the catalyst can vary with different preparation procedures. It is also possible that one support may be more able than another to absorb such ions to keep them away from the catalytically active sites on the metal.2 It is best to keep these matters in mind when evaluating any MSI data. 

A significant change in catalytic activity occurs when a metal-supported on a reducible oxide such as titania is heated in hydrogen at relatively high temperatures. For one thing these high temperature reduced (HTR) materials show a dramatic decrease in hydrogen and carbon monoxide chemisorption, a 

Stiles, Catalyst Supports and Supported Catalysts, (A. B. Stiles, Ed.) Butterworths, Boston, 1987, p 87. 

Anderson, Structure of Metallic Catalysts, Academic Press, New York, 1975, p 41. 

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It is now well established that spillover-backspillover phenomena play an important role in numerous catalytic systems. It is worth reminding that the effect of strong-metal-support interactions (SMSI), which was discovered by Tauster74 and attracted the intense interest of the catalytic community for the least a decade75 was eventually shown to be due to backspillover of ionic species from the Ti02 support onto the supported metal surfaces. 

S.J. Tauster, S.C. Fung, and R.L. Garten, Strong metal-support interactions. Group 8 noble metals supported on T1O2, JACS 100, 170-175 (1978). 

To Illustrate the utility of the technique, we have addressed the question of the anomalous chemlsorptlve behavior of tltanla-supported group VIII metals reduced at high temperatures. The suppression of strong H2 chemisorption on these catalysts has been ascribed to a strong-metal-support Interaction (SMSI) ( ). It has also been found that the reaction activity and selectivity patterns of the catalysts are different In normal and SMSI states... 

The interactions between metals and supports in conventional supported metal catalysts have been the focus of extensive research [12,30]. The subject is complex, and much attention has been focused on so-called strong metal-support interactions, which may involve reactions of the support with the metal particles, for example, leading to the formation of fragments of an oxide (e.g., Ti02) that creep onto the metal and partially cover it [31]. Such species on a metal may inhibit catalysis by covering sites, but they may also improve catalytic performance, perhaps playing a promoter-like role. 

The structure of supported rhodium catalysts has been the subject of intensive research during the last decade. Rhodium is the component of the automotive exhaust catalyst (the three-way catalyst) responsible for the reduction of NO by CO [1], In addition, it exhibits a number of fundamentally interesting phenomena, such as strong metal-support interaction after high temperature treatment in hydrogen [21, and particle disintegration under carbon monoxide [3]. In this section we illustrate how techniques such as XPS, STMS, EXAFS, TEM and infrared spectroscopy have led to a fairly detailed understanding of supported rhodium catalysts. 

At the end of the seventies, scientists at Exxon discovered that metal particles supported on titania, alumina, ceria and a range of other oxides, lose their ability to chemisorb gases such as H2 or CO after reduction at temperatures of about 500 °C. Electron microscopy revealed that the decreased adsorption capacity was not caused by particle sintering. Oxidation, followed by reduction at moderate temperatures restored the adsorption properties of the metal in full. The suppression of adsorption after high temperature reduction was attributed to a strong metal-support interaction, abbreviated as SMSI [2]. 

We conclude that strong metal-support interaction is in fact an incorrect name for a phenomenon which is satisfactorily explained by the blocking of adsorption sites due to the covering of metal particles by mobile oxide species from the support. Additionally, these oxide species may act as promoters in catalytic reactions. 

Kalakkad, Datye, and coworkers—TEM indicates strong metal-support interactions in Pt/ceria and Pt/Ce/Al catalysts. Kalakkad et al 362,369 published TEM and probe reaction studies on 0.6%Pt/CeO2 catalysts relevant to ACC catalysis. The... 

Imamura, Kaito, and coworkers—metal-support effects observed after calcination. Imamura et al 9X reported a strong metal-support interaction between Rh and Ce02, whereby high surface area ceria calcined at low temperature (550 °C) was able to transport Rh particles to the bulk, as measured by XPS. They suggested that despite the low degree of exposure of the Rh particle at the surface, the exposed Rh was highly active for the methanol decomposition reaction. 

The crystalline structure of the metal is also affected by the metal-support interaction. Metal particles supported on CNFs have a highly crystalline structure due to strong metal-support interaction [155], whereas Pt particles supported on Vulcan and OMCs have a more dense globular morphology due to weak metal-support... 

The use of supports such as Ti02, where the effect of a strong metal-support interaction (SMSI) was observed at high reduchon temperature, is one of the recommended routes. It is proposed that TiO having coordinatively unsaturated Ti cations that could interact with the electron pair donor site of the C=0 bond, facilitates adsorption of the unsaturated aldehyde in a favorable way to produce UOL [74, 75]. As for the metaUic phase, both theoretical and experimental studies indicate that larger particles improve the selectivity to UOL. In effect, it has been... 

The phenomena which occur in metal-ceramic interface interactions are of great importance in catalysis. There are two types of interactions those which depend on the epitaxy between the metal and the support and those which are independent of it. Strong metal-support interactions are described by the term SMSI. 

Strong metal-support interactions (SMSI) and electronic structures In situ atomic resolution ETEM... 

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