Metal-Support Interactions MSI

A variety of metal-support effects can occur to alter the adsorptive and/or catalytic behavior of a metal surface, and these include 1) Incomplete reduction of the metal 2) Support-induced cluster size 3) Epitaxial growth 4) Particle morphology 5) Contamination by the support 6) Bifunctional catalysis 7) Spillover and porthole phenomena and 8) Charge transfer between a metal and a semiconductor [2]. In addition, one might cite the stabilization of extremely small (1-3 atom) metal clusters on a support [7]. 

there is one additional type of metal-support effect that was originally termed SMSI (Strong Metal-Support Interactions) by the researchers at Exxon, where it was discovered [8], and its presence using a reducible oxide support was demonstrated by a marked decrease in H2 and CO chemisorption capacity, especially the former, with no increase in metal crystallite size, i.e., no decrease in dispersion [8]. This was subsequently shown to be primarily due to reduction of the support accompanied by its migration or the migration of one of its suboxides onto the metal surface, thus causing decreased chemisorption capacity due to physical blockage of 

Boudart and G. Djega-Mariadassou, Kinetics of Heterogeneous Catalytic Reactions , Princeton University Press, Princeton, NJ, 1984. 

Boudart, Kinetics of Chemical Processes , Prentice-Hall, Englewood Cliffs, 

An Introduction to Chemical Engineering Kinetics Reactor Design , J. Wiley, NY, 1977. 

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Prereduced at 500 °C, Metal-Support Interaction (MSI) suppressed CO adsorption. 

The NEMCA effect is closely related to classical promotion and to the phenomenon of metal-support interactions (MSI) with oxide supports and that MSI can be viewed as a self-driven NEMCA microsystem where the promoting O2- ions are thermally migrating from the support to the dispersed catalyst nanoparticles and replenished in the support by gaseous 02 [v]. 

It appeared finally that the support can no longer be considered as a pure inert stabilizing partner. Actually, the support acts as a supramolecular ligand and has been claimed to promote specific electronic properties and/or geometrical features of the nano-sized supported metal particles. Any metal-support interaction (MSI) does occur in any case when small particles are deposited on a carrier. However, the extent of their interaction depends on the nature of the metal, but much more on the size of the particles and the nature of the support. 

Pt-Sn/Al 03 is one of lhe most important commercial bimetallic catalysts for j i fnrining and dehydrogerm I ion of hydrocarbon feedstocks. Pre ious investiga-1 ii-ns refs 4-Ti) have shown that the state of the tin component as well as the of metal-support interaction (MSI) and metal-metal-interaction (MMI) exerl grcoi influence on the properties of this type of catalyst. It lias also beer found that Ihcse characteristics uf the catalysts not only depend on the preparation techniques of the calalysis, but also on the treatment condi-... 

A possible mechanism for the hydrogenation of carboxyl bond over titania supported ruthenium catalyst with the involvement of Metal Support Interaction (MSI) is seen in Scheme 6. The reaction proceeds via the formation of alkoxide surface intermediates. 

A new preparation method is described to synthesize porous silicon carbide. It comprises the catalytic conversion of preformed activated carbon (extrudates or granulates) by reacting it with hydrogen and silicon tetrachloride. The influence of crucial convoaion parameters on support properties is discussed for the SiC synthesis in a ftxed bed and fluidized bed chemical vapour deposition reactor. The surface area of the obtained SiC ranges ftiom 30 to 80 m /g. The metal support interaction (MSI) and metal support stability (MSS) of Ni/SiC catalysts are compared with that of conventional catalyst supports by temperature programmed reduction. It is shown that a Ni/SiC catalyst shows a considnable Iowa- MSI than Ni/Si(>2- and Ni/Al203-catalysts. A substantially improved MSS is observed an easily reducible nickel species is retained on the SiC surface after calcination at 1273 K. 

The chemical species present on the support surface interact, more or less, with the metal nanoparticles deposited thereon. This phenomenon is currently called as metal-support interaction (MSI) and is usually stronger when the metal particles are smaller. It regulates the mobility of metal atoms and clusters on the support surface. In practice, when a strong metal-support interaction (SMSI) occurs, smaller (and more resistant to sintering) metal nanoparticles are usually obtained. 

Torr) [32-36], Alternatively, higher H2 pressures at 300 K can be used to both form the hydride and saturate the Pd surface with H atoms, then an evacuation step is used to rapidly decompose the bulk hydride, and this is followed by obtaining a second isotherm. Similar to the situation in Figure 3.3, the difference, a, represents the irreversible H adsorption on the Pd surface. This approach may be preferred because it provides additional information about the Pd crystallites, i.e., once the surface Pds atoms are counted by the irreversible uptake, the remainder of the atoms can be attributed to bulk (Pdb) atoms, i.e., Pdb = Pdt Pds, and the apparent bulk hydride ratio can be determined [32]. Values near PdHo b are typically attained with large clean Pd crystalhtes, but on small Pd crystallites this apparent hydride ratio can become larger than 0.6 because reversible chemisorption on the Pds atoms can dominate the second isotherm as the Pd dispersion approaches unity. Consequently, valuable information can be obtained regarding surface cleanliness and metal-support interactions (MSI) [32,37]. An example of such an effort is provided by Illustration 3.1. 

The dependencies of the electronic properties on cluster size have been interpreted both by intrinsic ( initial state ) and spectroscopy-induced ( final state ) effects. A separation of both effects is difficult, especially in view of an unknown influence of metal-support interaction (MSI) and of sample charging effects (different for insulating, semiconductive, or conductive substrates). See [3, 4], and the comments on PES of supported metal clusters in [6], and further discussions in [7, 8]. 

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