Fischer-Tropsch reaction on Co-containing microporous and mesoporous Beta zeolite catalysts: the effect of porous size and acidity

Abstract

• The most active catalyst was Red-Me-CoSiBeta with CO conversion of 91%. • Red-Mi-CoSiBeta was less active than Red-Me-CoSiBeta. • With CO conversion of 71.6% and selectivity towards liquid products of 86.6%. • Red-Mi-CoSiBeta more selective towards isoalkanes than Red-Me-CoSiBeta. • Formation of the bigger cobalt nanoparticles is the key factor of FTS. This work deals with the investigation of the influence of the preparation procedure on the activity of microporous and mesoporous CoBeta zeolite in Fischer – Tropsch synthesis (FTS). The series of CoSiBeta, CoAlSiBeta and CoAlBeta zeolites were prepared by: i) two-step postsynthesis procedure (CoSiBeta with totally dealuminated Beta and CoAlSiBeta with partially dealuminated Beta) and ii) classical wet impregnation (CoAlBeta with undealuminated Beta), respectively. The calcination of as prepared CoSiBeta, CoAlSiBeta and CoAlBeta zeolites at 500 °C, for 3 h in the air and then reduction by treatment in flowing H 2 at 400 °C for 1 h allows to obtain Red-C-CoAlBeta, Red-C-CoAlSiBeta and Red-C-CoSiBeta catalysts with different properties in Fischer – Tropsch reaction. The two-step postsynthesis method allowed obtaining very active, more stable and more resist to carbon deposition catalysts. Two series of zeolite catalysts were prepared using microporous (Mi) and mesoporous (Me) supports. The most active catalysts in Fischer-Tropsch synthesis was Red-Me-CoSiBeta with high CO conversion of 91% and selectivity towards liquid products of 88.9% and Red-Mi-CoSiBeta with CO conversion of 71.6% and selectivity towards liquid products of 86.6%. Such results seem to be related to the formation of the larger cobalt nanoparticles on SiBeta support than on HAlSiBeta and HAlBeta supports. Larger particles exhibit weaker interaction with the support and hence, higher activity in Fischer-Tropsch synthesis. Red-Mi-CoSiBeta zeolite catalyst shows much higher selectivity towards isoalkanes than Red-Me-CoSiBeta with the ratio isoalkanes/n-alkanes of 1.32 for Red-Me-CoSiBeta and of 2.38 for Red-Mi-CoSiBeta.