High pressure (<= 5.1 MPa) DRIFT study on surface structure of Co-Mo/Al2O3and Ni-Mo/Al2O3 using NO as probe molecule

The surface structures of Co-Mo/Al2O3 and Ni-Mo/Al2O3 sulfided at 0.1-5.1 M Pa were investigated by the in situ DRIFT of adsorbed NO and Mo K-edge EXAF S. The relative intensities of IR bands of NO adsorbed on Co-Mo/Al2O3 and N i-Mo/Al2O3 changed depending on the pressure of sulfiding. It was indicated that CUS were selectively formed on the promoters of Co-Mo/Al2O3 and Ni-Mo /Al2O3 when the catalysts were sulfided above 1.1 MPa, In other words, CUS of Mo disappeared by higher pressure of sulfiding. On the other hand, Mo K- edge EXAFS indicated that MoS2-like structure of Co-Mo/Al2O3 was not sinter ed by higher pressures of sulfiding. Based on these results, it is conclude d that the selective formation of CUS on the promoters of Co-Mo/Al2O3 and N i-Mo/Al2O3 is caused by Co-Mo and Ni-Mo interaction by higher pressure of s ulfiding resulting in the selective capping of CUS on Mo by the promoters. (C) 1999 Elsevier Science B.V. All rights reserved.