Strong metal support interactions SMSI

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. 

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 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... 

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

During the late 1970s, 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 as 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 (SMSI) [2]. 

Metal-support interactions have been recently reviewed by Bond (93), who drew special attention to catalysts that gave evidence for strong metal-support interactions (SMSI). This condition was first observed in 1978 by Tauster et al. (94) for Pt on titania catalysts. The catalysts seemed to lose their capacity for H2 and CO chemisorption but nevertheless retained and enhanced their activity for only two types of reaction methanation and Fischer-Tropsch synthesis. Since then a considerable number of papers devoted to SMSI studies have been published all over the world. 

Ceria/noble metal (such as Ru, Rh, and Pd) catalysts are composed of noble metal species such as nanoparticles and clusters dispersed on the ceria supports. The catalysts show typical strong metal-support interactions (SMSI) (Bernal et al., 1999), that is, the catalysts exhibit a number of features for SMSI effects including (1) reducible supports (2) "high temperature" reduction treatments (3) heavily disturbed chemical properties and significant changes in catalytic behavior of the dispersed metal phase (4) reversible for recovering the conventional behavior of the supported metal phase. In these cases, the reducibility of ceria NPs is greatly enhanced by the noble metal species and the catalytic activities of the noble metals are enhanced by ceria NPs. 

Metal-support interactions can be defined as being weak, medium or strong.28 Non-reducible metal oxides such as silica, alumina, and magnesia as well as carbon or graphite are considered to exert only a weak influence on the metal and, thus, exhibit only a weak metal-support interaction (WMSI). Zeolites (Chapters 10 and 13) exert a medium metal-support interaction (MMS1)28 while metals supported on reducible oxides when reduced at high temperatures exhibit a strong metal-support interaction (SMSI).27-32... 

Jennison DR, Dulub O, Hebenstreit W, Diebold U (2001) Structure of an ultrathin TiO film, formed by the strong metal support interaction (SMSI), on Pt nanocrystals on UO ll 10). Surf Sci 492 L677... 

The phenomenon of strong metal-support interactions (SMSI) discovered by Tauster et al. [96] which attracted worldwide attention for many years [7]. 

Titania-supported Metals. - After reduction at 473 K, platinum-group metals supported on Ti02 chemisorbed both hydrogen and carbon monoxide in quantities indicative of moderate-to-high dispersion, but following reduction at 773 K chemisorption was drastically lowered e.g., H/Mt <0.01 for Pt, Ir, and Rh, 0.05-0.06 for Pd and Ru, and 0.11 for Os). Agglomeration, encapsulation, and impurities were eliminated as possible causes and a strong metal-support interaction (SMSI) was proposed. Titania is not unique in its SMSI properties and 11 oxides used to support iridium were classified as follows ... 

One of the main aspeets that determine the properties of a given catalyst is the nature of the interaction between the oxide support and the dispersed active metal. The influence of this interaction on the activity, selectivity and stability of the catalyst is determined by factors such as the preparation method, the atmosphere and temperature of the calcination and reduction stages (1,2), and the specific metal-support system studied. The latter is especially important for catalysts based on transition metals supported on partially reducible oxides (3). Such catalysts displaying strong metal-support interaction (SMSI) exhibit suppression of chemisorption of H2 and CO (4-6) when reduced at temperatures up to 773 K. 

Ti02 catalysts reduced at 700°K and is presently accepted as the key step in the induction of strong metal-support interaction (SMSI). The present observation appears to be the first case in which SMSI can be induced at normal (500 K) catalyst reduction temperatures. High resolution electron energy loss spectroscopy (EELS) experiments of CO on Ni/Mn0x reduced at 500°K showed dramatic reduction of the C-0 stretching frequency of adsorbed CO. These EELS results are discussed in light of... 

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