Fritz Vogt

Acidity of aluminophosphate structures. Part 1.—Incorporation of sillicon into chabazite-like structure 44

SAPO-44 samples have been prepared with different silicon contents up to 34.3 mass% SiO2. Characterization of the samples by X-ray diffraction (XRD), thermal analysis, adsorption measurements, chemical analysis, microprobe analysis and IR spectroscopy reveals that the samples are highly crystalline, even those with the highest SiO2 content. The number of Bronsted acid sites determined by NH3 sorption [calorimetric and temperature-programmed desorption (TPD) measurements] is independent of the SiO2 content of the samples and amounts to about one acid centre per double-six-ring of the chabazite-like structure.Concerning the silicon ordering within the framework, it is proposed that aluminophosphate-based as well as aluminosilicate-based double-six-rings form the structure.

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.