CATALYST PREPARATION VARIABLES THAT AFFECT THE CREATION OF ACTIVE-SITES FOR HDS ON CO MO/AL2O3 CATALYTIC MATERIALS/

In a recent paper (J. Catal, 158, 411, 1996) we demonstrated that the intensity of a specific peak (pK similar to 6) in proton affinity dist ributions (PADs) measured for a series of Co-Mo/Al2O3 catalysts could be correlated to the variation in HDS activity within the series. PADs access information about species on the catalyst's surface from analy ses of proton binding data collected using potentiometric titration. I f the species determined at the solid/aqueous interface are present af ter catalyst activation and are active during catalytic testing, then this methodology can provide a simple, surface sensitive procedure for catalyst characterization which should correlate with other character ization techniques. To test this hypothesis we provide herein results from more conventional catalyst characterization techniques in order t o corroborate the PAD results. The techniques of temperature-programme d reduction, X-ray photoelectron spectroscopy, and laser Raman spectro scopy were used to provide additional characterization of Co-Mo/Al2O3 catalysts in their oxide state. PADs were obtained for this catalyst s ystem in their oxide and sulfided states, The HDS activity for each me mber of this series was measured using hydrodesulfurization of thiophe ne as a test reaction. The effect of cobalt loading, molybdenum conten t, presulfidation conditions, and pH during catalyst preparation were the variables used, Based on the experimental data we propose that the active site for HDS activity is a Co-Mo interaction species consistin g of molybdate octahedra and a dispersed Co which could also be octahe drally coordinated. This species can be transformed reversibly during the processes of sulfidation and reoxidation and its formation is cont rolled by pH. (C) 1996 Academic Press, Inc.