Effect of CyDTA on the coordination structure around Ni atom during the preparation steps for NiMo and NiW hydrodesulfurization catalysts

Introduction NiMo/Al2O3 and NiW/Al2O3 catalysts are widely used for the hydradesulfurization (HDS) and hydrogenation (HYD) reactions of petroleum feedstock. It is an urgent issue to improve their catalytic activity to meet severe regulations for the sulfur content of the transportation fuels. These catalysts are usually prepared by impregnating Al2O3 support with an aqueous solution containing Ni and Mo (or W). The impregnated materials are further underwent a drying process and finally sulfided before the reaction. Recently, the authors found that the addition of some chelating agents such as CyDTA to the impregnation solution greatly improves their HDS and HYD activities [1, 2]. Thermodynamic calculations imply that CyDTA forms a stable complex with Ni ion in the impregnating solution, which survives during the impregnation and drying process and eventually affects the sulfide structures [2]. However, no direct evidence for the role of CyDTA during the preparation steps has been reported yet. Therefore, the present study has investigated the coordination structure around Ni atoms during the preparation of NiMo and NiW catalysts by Ni K-edge EXAFS. The local structures around Mo and/or W atoms in these catalysts are also reported in the separate report.