TITLE: CO hydrogenation over cobalt Fischer-Tropsch catalysts.

AUTHOR: A. Hoff.

INST.  AUTHOR: Norges Tekniske Hoegskole, Trondheim.


PUB.  TYPE: Thesis


SOURCE: Department of Energy [DEE],  Oct 93,  204p.  ISBN: 82-7119-556-5



The main aim of the present work has been to study in what way the addition of a second metal influences the CO hydrogenation rate over alumina supported cobalt catalysts. Temperature programmed reduction studies (298-1173 K) show that the calcined 9% Co/Al(sub 2)O(sub 3) contains two main cobalt phases: Crystalline Co(sub 3)O(sub 4) particles and a cobalt oxide layer containing cobalt ions interacting with the alumina support surface. Some amounts of heavily reucible CoAl(sub 2)O(sub 4) are also present in the catalyst. Addition of 0.1 and 1.0 wt% Pt from a chloride containing precursor lowers the temperature for Co(sub 3)O(sub 4) reduction with about 80 K, while the reduction temperature of the oxidic cobalt surface layer is lowered with 100-200 K compared to the monometallic cobalt catalyst. The temperature shift increases with increasing platinum amount. 1 wt% Pt from a chloride free platinum precursor increases the shift for the reduction of Co(sub 3)O(sub 4) to140 K, while reduction of the cobalt surface phase is shifted 100 K compared to the monometallic catalyst. Other second metals (Pd, Ru, Ir or Re) also lowers the cobalt reduction temperature. The size of the shift depends on the type of metal. It is suggested that the second metal must be reduced itself before it promotes the reduction of cobalt. It is found that the bimetallic CoPt and CoRe catalysts are reduced to a larger extent compared to the monometallic cobalt catalyst during an isothermal reduction for 16 hours at 623 K. In the bimetallic catalysts the oxidic cobalt surface layer are reduced, while this is not the case for the monometallic catalyst. Both the extent of decomposition of cobalt nitrate during the calcination and the reductive decomposition temperature are unaffected by addition of a second metal. (ERA citation 19:032351)