2608.     ---------------.  [PERRIN, M.]  [Chemical Evolution of Fischer Catalysts During the Thermal Reducing Treatment.]  Compt. rend., vol. 227, No. 8, 1948, pp. 476-478; Bull. soc. chim., 1949, No. 5-6, pp. 366-367; Chem. Abs., vol. 43, 1949, p. 26.

        Ni catalysts on kieselguhr with small amounts of ThO₂ or Al₂O₃ were subjected to reducing tests in order to ascertain, as  function of time and temperature, the loss in weight and the amounts of H₂O and CO₂ set free.  The catalyst, after drying, tested 26.3% of Ni, the transformation of which to the metallic state involved a loss of 7.2%.  A rapid heating up to 450° in a stream of H₂ for 127 min. caused a loss in weight of 24.8%, and in N₂, 24%.  The same catalyst calcined in air at 900° lost 26.4% of its weight.  The brief treatment up to 450° had an almost identical result and was enough to eliminate almost the whole amount of CO₂ and H₂O in the basic carbonates and the other hydrated substances that made up the dried catalyst.  With a slower treatment of gradual heating up to 450° during a period of 4 hr., the loss in weight was 28.5%.  There was an increased reduction of the NiO.  The H₂O and CO₂ set free measured, respectively, 21.4 and 4.85% of the initial weight, the deficit of 2.25% being CH₄, which was carried away in the stream of H₂.  At the end of a series of operations at different temperatures and times, the weight of the catalyst had diminished 32.5-32.8%, a result very close to that obtained by calcination in air at 900°, including the total reduction of the NiO (26.4%+7.2%=33.6%).  These empirical results, however, do not necessarily agree with general practice; many factors may modify the results.  The rate of temperature increase, the length of treatment, and the flow of H₂ affect the various chemical reactions involved such as dehydration, decarbonation, reduction of CO₂ to CH₄, and reduction of NiO.  The same parameters must likewise influence the formation of hydrated combinations between the silica of the kieselguhr, the Al₂O₃, and the oxides of the heavy metals, as these combinations are formed very easily under the conditions of preparation and reduction of Fischer catalysts.