ELECTRON-MICROSCOPY STUDY OF NIW AL2O3-F(X) SULFIDED CATALYSTS PREPARED USING OXISALT AND THIOSALT PRECURSORS/

Two different series of sulfided NiW catalysts supported on alumina mo dified with different amounts of fluoride, in the range 0.0-2.5 wt%, h ave been prepared by using two different tungsten precursor salts: amm onium metatungstate and ammonium tetrathiotungstate. Samples of both c atalyst series have been examined by the use of high-resolution electr on microscopy. For the oxisalt-prepared catalysts the results indicate that fluoride incorporation increases the size of WS2 crystallites bu t has little effect on the number of layers. On the other hand, the ch ange of precursor salt significantly influences the stacking of WS2 cr ystallites without greatly affecting their size. The thiosalt method o f preparation also leads to an excess of sulfur in the catalysts, whic h is distributed in a nonhomogeneous way. (C) 1996 Academic Press, Inc .