Thermal decomposition of bulk K-CoMoSx mixed alcohol catalyst precursors and effects on catalyst morphology and performance

Cobalt molybdenum sulfide-type mixed alcohol catalysts were synthesized via calcination of precipitated bulk sulfides and studied with temperature programmed decomposition analysis. Precursors containing aqueous potassium were also considered. Precipitates thermally decomposed in unique events which released ammonia, carbon dioxide, and sulfur. Higher temperature treatments led to more crystalline and less active catalysts in general with ethanol productivity falling from 203 to 97 g (kg cat)−1 h−1 when the calcination temperature was increased from 375 to 500 °C. The addition of potassium to the precursor led to materials with crystalline potassium sulfides and good catalytic performance. In general, less potassium was required to promote alcohol selectivity when added before calcination. At calcination temperatures above 350 °C, segregated cobalt sulfides were observed, suggesting that thermally decomposed sulfide precursors may contain a mixture of molybdenum and cobalt sulfides instead of a dispersed CoMoS type of material. When dimethyl disulfide was fed to the precursor during calcination, crystalline cobalt sulfides were not detected, suggesting an important role of free sulfur during decomposition.

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► Lower-temperature thermal treatments of K-CoMoSx mixed alcohol catalyst precursors result in higher specific activity.
► Addition of K to catalyst precursor leads to finished materials with different morphology and performance.
► Cobalt segregates from the catalyst precursor during calcination to form bulk cobalt sulfides.
► Addition of gas phase sulfur during calcination reduces or eliminates segregation of cobalt.