Support oxygen atoms

The LTL zeolites have a Si/Al ratio of 3.027. Based upon the crystallographic formula of LTL ([K9(H20)2i][Al9Si27072]), the number of Bronsted acid sites in the LTL with a K/Al = 0.47 is 1.76 mmol/g. In the case of the LTL [0.82], this is 0.57 mmol/g. The LTL zeolites with K/A1>1 have no Bronsted acid sites, and after calcination at elevated temperatures, the excess K is probably present as KOH or K20. Increased amounts of K results in a more basic support, with an increased electron-richness on the support oxygen atoms. ... 

Fourth, a bond is formed between the support and metal particle, mainly via the interstitial bond orbital of the metal particle. For a basic support with electron rich support oxygen atoms, electrons are donated to the Pt particle and the IBO is geometrically located at the surface of the metal particle. The opposite occurs for acidic supports, where Pt particles becomes positively charged and the IBO is geometrically located at the metal-support interface region. Since reactants will adsorb on the metal via this IBO, the different geometrical locations will have large effects on the catalytic properties of a supported Pt catalyst. 

As mentioned above, the support has three effects on the electronic structure of supported Pt particles. An increasing electron richness of the support oxygen atoms results in (i) a shift in the total density of states to higher energy, (ii) rearrangement of the s-p states within the particle from the particle-support interface to the particle surface and (iii) rehybridization of the valence band to more 6sp and less 5d character. A crucial question to answer is how these change in s,p and d-states influences the chemisorption of H and CHX on the Pt particles. 

In an earlier paper, it was shown that the location of the IBO within the Pt particle shifts from the metal-support interface to the Pt surface with increasing electron richness of the support oxygen atoms (more basic support)18,19. In addition, some anti-bonding 6sp states are shifted below the Fermi-level and become populated at the cost of the Pt 5d. This can also be seen when the H DOS on Pt4/F20 (Figure 3) and Pt4/Na20 (Figure 4) are compared. There are 178... 

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