95/05792 The effect of catalyst dispersion on the activity of unsupported molybdenum catalysts

Abstract

Unsupported catalysts have received considerable attention for coal liquefaction. These catalysts have been introduced into coal liquefaction systems by impregnation of the coal, as water-soluble salts, as volatile metal carbonyls, as oil-soluble organometallics, as finely divided powders, and as mineral matter associated with the coal and/or solvent. For the most part, the method of catalyst precursor addition affected the observed catalyst performance. Weller et al. found that, with ammonium heptamolybdate, coal impregnation resulted in higher coal conversions than physical mixing of the powder with coal. Others have also observed this result. Additionally, Derbyshire et al. found that the conditions used to dry the impregnated coal (removing the aqueous solvent used for solubilizing the catalyst precursor) affected the activity of the molybdenum. Joseph and Artok et al. reported that expanding the coal structure (by swelling during impregnation) improved the observed activity of the catalyst, possibly by allowing better contacting of the coal with the catalyst. Schlesinger et al. found that results approaching those of impregnated MOS{sub 2} could be obtained by thoroughly mixing a powdered catalyst with the coal using a ball-mill.