PETR 76 |
| Additivation of hydrotreating catalysts by glycol molecules is an efficient procedure to improve catalytic activity. Nevertheless, controversial explanations about the activity enhancement mechanism exist in the literature. This may be due to different catalyst preparation procedures, different additivation methods or simply because several phenomena are implied in these improvements. The aim of this work is thus to rationalize the roles of additivation with respect to (i) species present in the impregnation solution as well as on the catalyst surface and (ii) the preparation step where additivation is performed, i.e. after drying or after calcination. Different impregnation solutions have been used containing a) ammonium heptamolybdate or cobaltomolybdate heteropolyanions for CoMo catalysts and b) phosphomolybdate heteropolyanion with different P/Mo molar ratio for CoMoP catalysts. Surface species have been thoroughly characterized for dried and calcined catalysts prior to and after additivation by triethyleneglycol. For all dried and calcined CoMo and CoMoP catalysts, a redissolution phenomenon has been evidenced after additivation, leading to the formation of the Anderson heteropolyanion AlMo6O24H63-. This redissolution phenomenon is however limited by the low solubility of AlMo6O24H63-. Moreover, in the case of CoMoP dried catalysts (P/Mo molar ratio ³0.4), characterization of additivated catalysts evidenced PCoMo11O407- formation. Redissolution and redispersion due to additivation are thus enhanced because phosphomolybdic species have a much higher solubility than AlMo6O24H63-. Similar observations, although less pronounced, may be drawn for calcined catalysts. Indeed, a stronger precursor-support interaction has been created during calcination. Catalysts performances were evaluated in toluene hydrogenation and activities obtained match perfectly. |
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3rd International Symposium on Hydrotreating/Hydrocracking Technologies
1:30 PM-4:20 PM, Tuesday, August 21, 2007 Boston Park Plaza -- White Hill Rm, Oral
Division of Petroleum Chemistry |