Activity and surface structure of sulfided NiW/Al2O3 catalyst:: Effects of chelating agents on the catalytic activity for the hydrogenation of tetralin and o-xylene

The present study investigated the effects of chelating agents on the aromatic hydrogenation activity and the surface fine structure of NiW/Al2O3 catalyst. NiW/Al2O3 catalyst was prepared from impregnating solution containing Ni, W and chelating agent (IDA, NTA, DTPA, EDTA, TTHA and/or CyDTA) and used for the hydrogenation of tetralin and o-xylene. NiW/Al2O3 Prepared with chelating agents showed higher activities than NiW/Al2O3. CyDTA was the most effective additive for both reactions. NiW/Al2O3 prepared with CyDTA also showed higher activity than commercial NiW catalyst. NO pulse adsorption and XPS measurements indicated that the addition of chelating agents improved the dispersion of Ni species. W L-III-edge EXAFS measurements showed that the W-S coordination number of WS2 was improved by the addition of CyDTA. These results suggest that the chelating agent enhances the formation of the Ni-W-S structure. Chelating agent forming a stable complex with Ni in the impregnating solution had a greater promoting effect on hydrogenation activity. Formation of the stable chelate-Ni complex affects the sulfidation process of Ni species during the sulfiding pretreatment, which enhances the formation of the active Ni-W-S structure.