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 degrees 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 degrees 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 Co-Mo-S 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. (C) 2012 Elsevier B.V. All rights reserved.