STRONG METAL-SUPPORT INTERACTIONS transformations

Abbreviations BCC. body centered cubic DOS. density of states ESR. electron spin resonance HX.AI S, extended X-ray absorption fine structure F CC. face centered cubic (a crystal structure). FID, free induction decay FT, Fourier transform FWHM, full width at half maximum HCP, hexagonal close packed HOMO, highest occupied molecular orbital IR, Infrared or infrared spectroscopy LDOS, local density of states LUMO, lowest unoccupied molecular orbital MAS. magic angle spinning NMR. nuclear magnetic resonance PVP. poly(vinyl pyrrolidone) RF. Radiofrequency RT, room temperature SEDOR, spin echo double resonance Sf, sedor fraction SMSI, strong metal-support interaction TEM. transmission electron microscopy TOSS, total suppression of sidebands. 

As the dissociative adsorption of H2 requires the presence of multiple-vacancy sites (at least two vacancies on the same metal atom, or two adjoining vacancies on nearby atoms are needed), this is a further indication of a strong Ce02/Pt interaction that renders virtually null the probability of multiple-vacancy sites (ii) When the y-Al203 -. G-AUOj phase transformation occurs in the presence of Pt, all the adsorptive capacity of ACe rPt catalysts is lost. Although the surface area of the catalyst still remains appreciable (see Table 1), the transformation of the porous texture (dealt with in a previous work [6]) and the modified metal-support interaction buries all the available Pt, so that the catalysts become inactive. 

Obviously, use of such databases often fails in case of interaction between additives. As an example we mention additive/antistat interaction in PP, as observed by Dieckmann et al. [166], In this case analysis and performance data demonstrate chemical interaction between glycerol esters and acid neutralisers. This phenomenon is pronounced when the additive is a strong base, like synthetic hydrotalcite, or a metal carboxylate. Similar problems may arise after ageing of a polymer. A common request in a technical support analytical laboratory is to analyse the additives in a sample that has prematurely failed in an exposure test, when at best an unexposed control sample is available. Under some circumstances, heat or light exposure may have transformed the additive into other products. Reaction product identification then usually requires a general library of their spectroscopic or mass spectrometric profiles. For example, Bell et al. [167] have focused attention on the degradation of light stabilisers and antioxidants... 

Chemical interactions between metal and support are also observed on main group metal oxides such as Si02, AI2O3, and MgO, which can normally be regarded as chemically highly inert. Strong interactions have also been found between various metals of Groups 8-10 and carbon supports. Palladium and nickel form carbide phases, and the transformation of carbon and the encapsulation of metal crystallites have been proven [18],... 

---