Studies of molybdenum sulfide catalysts: I. Oxygen chemisorption on unsupported and supported MoS 2

Abstract

The use of low-temperature oxygen chemisorption (LTOC) to characterize molybdenum sulfide catalysts has become common, but the values of LTOC are very sensitive to details of catalyst pretreatment. For unsupported MoS 2, the previously reported values for the ratio of BET surface area to LTOC, expressed as A ̊ 2 O 2 , have varied over a 10-fold range. Three samples of MoS 2, prepared by different routes in three laboratories, have now been shown to give values for this ratio which fall in the narrow, and low, range of 84 to 103 A ̊ 2 O 2 , provided that a common pretreatment in H 2 at 450 °C precedes the LTOC measurement. (Prereduction is standard practice for characterization of MO oxide catalysts by LTOC.) Application of the same methodology to a sulfided molyb-dena-alumina sample gives values for LTOC which are much higher than those previously reported for similar (but not H 2-pretreated) samples. LTOC on the sulfide is about 20% lower than that on the same sample in the oxide (reduced-only) condition, and the values after a given pretreatment—reduced-only, or sulfided and reduced—are auite reproducible when the supported catalyst is cycled at 450 °C.