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Abstract

Gamma-alumina samples precalcined at 773 or 1073 K, respectively, were coimpregnated with approximately 10 w/w% Co and Mo in the molar ratio Co/(Co + Mo) = 0.65. These catalyst precursors were subjected to a second heat treatment at 723 or 1073 K. The catalytic activity of calcined, prereduced and presulfided (by H2S) samples was checked in the HDS reaction of thiophene model compound in H-2. The ''apparent surface percentages'' of catalyst precursors and used catalysts - monitoring lines of Co, Mo, Al and also S and C - were determined by XPS. These values are not equal to the nominal bulk compositions and depend on the support and catalyst treatments. Possible correlations between the catalytic activity and the apparent surface percentage of Mo, Co and S are evaluated. High-temperature pretreatment of the support is advantageous for catalytic activity and so is a high-temperature calcination of the catalyst itself; highest activity is observed when these treatments are followed by presulfidation.