Studies of molybdena-alumina catalysts: XVI. Effect of high-temperature sulfiding

Abstract

Candia et. al. recently reported an increase in hydrodesulfurization (HDS) activity of CoMo/Al{sub 2}O{sub 3} catalysts sulfided at 600 C. They attributed the increase in activity to a more active CoMoS phase (Type II) compared to the regular Type I CoMoS phase found in catalysts sulfided at 400 C. Breysse et. al. found a similar effect with NiW/Al{sub 2}O{sub 3} catalysts. Prada Silvy et. al., however, reported no change in HDS activity in sulfiding CoMo/Al{sub 2}O{sub 3} catalysts up to 700 C. In these studies, sintering of the support occurred due to the higher sulfiding temperatures employed compared with the original calcining temperature of the catalyst ({approximately}500 C). The authors decided to determine the effect of sulfiding temperature on the HDS and hydrogenation (HYD) activity of Mo and CoMo catalysts on an alumina support stabilized by calcining at a higher temperature than that used in the sulfiding treatments in order to avoid the complications due to support sintering during sulfiding. The catalysts were sulfided at 400, 550, or 700 C. Sulfided catalysts were characterized by CO{sub 2} and NO chemisorption using a pulse technique. At least duplicate measurements were made on each sample. Catalytic activities for HDS of thiophene andmore » HYD of hexene were carried out at 350 C and under atmospheric pressure in a fixed-bed reactor. Pseudo first-order rate constants were calculated from conversions.« less