Wolfgang Mörke

The state of metallic phase in alumina-supported platinum-chromium catalysts

Abstract The reduction behaviour and the phase composition of platinum-chromium samples (unsupported and on alumina carrier) were investigated with the help of temperature-programmed reduction (TPR), X-ray diffraction, ferromagnetic resonance (FMR) spectroscopy and ethane hydrogenolysis. Co-reduction and the formation of alloys was found to occur when H 2 PtCl 6 and (CrO 3 ) x were used as starting materials. Annealing of the samples above 500°C led to the formation of a ferromagnetic Pt 3 Cr superlattice. Addition of chromium to platinum/alumina attenuates the hydrogenolysis activity; annealing results in an additional strong decrease of this demanding reaction.

Catalytical conversion of silicon tetrachloride to trichlorosilane. Characterization of the nickel silicalite catalyst by ferromagnetic resonance spectroscopy

The formation of nickel silicide in the reaction between nickel supported on silicalite and a gas mixture (molar ratio, H2 : SiCl4= 6 : 1) is studied. By ferromagnetic resonance (FMR) based Curie temperature measurements, it was determined that the formation of metal silicides starts at 723 K. From the signal intensity, it follows that the Si content of the silicides increases with increasing temperature from ca. 1 atom% at 723 K up to 6 atom% at 865 K. The geff values suggest the presence of two kinds of alloy containing ca. 1 atom% Si: one kind, produced at temperatures up to 723 K, forms a shell layer at the surface of the Ni metal particle, and the other, generated by decomposition of silicon-rich silicides formed at 865 K, is homogeneously alloyed over the whole particle.