BETTER SULFIDE CATALYSTS THROUGH OPTIMIZED ACTIVE PHASE-SUPPORT INTERACTION

In this project, improved hydrotreating catalysts have been synthesize d by varying the active phase-support interaction. This interaction ha s been changed by differing the calcining procedures and choice of cat alyst precursors and carriers. The active phase consisted basically of molybdenum or tungsten disulphide, and Ni, Co, Cr or Fe as the promot er. Also phosphorus has been added as secondary promoter. As for the p reparation of the catalysts, a new type of carrier, filamentary carbon supported by alumina, has been synthesized. To improve the interactio n between Co and Mo in the active catalyst, nitrilotriacetic acid (NTA ) has been added as a complexing agent to a solution containing both m etal salts. Also, a new type of active phase precursor (acetylacetonat e) has been used with a number of solvents (water, ethanol, toluene). The final consequences of these variations have been investigated from a physico-chemical point of view in relation to the actual performanc e of the newly prepared catalysts in the hydrodesulphurization of thio phene. In the physico-chemical characterization of the catalysts, Moss bauer emission and absorption spectroscopy (MES, MAS), X-ray photoelec tron spectroscopy (XPS), extended X-ray absorption fine structure spec troscopy (EXAFS) and X-ray absorption near edge structure (XANES) have been used. As a result, a detailed model of the so-called 'Co-Mo-S' p hase could be proposed. Mossbauer experiments on the sulphidation of c arbon-supported Co and Co-Mo catalysts indicate the formation of Co sp ecies (consisting of Co and Co-Mo, respectively), which have the same spectral features in Mossbauer spectroscopy. Hence, care should be tak en into account when referring to the so called 'Co-Mo-S' phase. In ad dition, fingerprinting techniques such as TPR (temperature programmed reduction) and TPS (temperature programmed sulphidation) have been app lied extensively. The sulphided catalysts contain different sulphur sp ecies. The existence of a very reactive sulphur species called 'excess sulfur' is correlated with the hydrodesulphurization activity. A mode l has been developed describing the coke deposition on hydrotreating c atalysts under commercial reaction conditions. As a result, improved h ydrotreating catalysts have been developed and a better understanding of the fundamental characteristics of the catalysts has been acquired. Novel equipment has been developed. Two of its major features are a s imple design and the possibility for the in situ measurement of physic al parameters of the autoclave contents. For future development of the catalysts, a detailed kinetic analysis of their performance, and the application of in situ characterization techniques is of paramount imp ortance.