title: Structure of the active sites of Co-Mo Hydrodesulfurization catalysts as studied by magnetic susceptibility measurement and NO adsorption.
abstract: The elucidation of a molecular structure of the active sites (i.e., the Co-Mo-S phase) of Co-Mo hydrodesulfurization catalysts has received extensive attention. In the present study, we unambiguously determined, for the first time, the NO adsorption behavior and magnetic property of the Co-Mo-S phase by preparing unique Co-Mo/Al(2)O(3) catalysts (CVD-Co/MoS(2)/Al(2)O(3)), in which all the Co atoms are present as the Co-Mo-S phase. The catalysts were characterized by NO adsorption (pulse technique and FTIR), Co K-edge XANES, and the magnetic susceptibility and effective magnetic moment of Co. Nitric oxide molecules were adsorbed on 33% of the Co atoms in CVD-Co/MoS(2)/Al(2)O(3) after sulfidation and on only half of the Co atoms even after an H(2)-treatment of the sulfided catalyst at 573-673 K. The Co atoms in CVD-Co/MoS(2)/Al(2)O(3) exclusively exhibited an antiferromagnetic property, indicating that even-numbered Co atoms are interacting with each other in the Co-Mo-S phase. A Co-Mo/Al(2)O(3) catalyst, prepared by a conventional impregnation technique, was composed of the antiferromagnetic Co sulfide species as observed in CVD-Co/MoS(2)/Al(2)O(3) in addition to Co(9)S(8). On the basis of the NO adsorption behavior and magnetic property, it is empirically proposed that the structure of the Co-Mo-S phase is represented as a Co sulfide dinuclear cluster located on the edge of MoS(2) particles. The magnetic property of Co/Al(2)O(3) sulfide catalysts depended on the preparation method.
authors.affiliation: Department of Material Science, Shimane University, Matsue 690-8504, Japan. yokamoto@riko.shimane-u.ac.jp
authors.forename: Yasuaki
authors.initials: Y
authors.lastname: Okamoto
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Kawano
authors.forename: Takao
authors.initials: T
authors.lastname: Kawabata
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kubota
authors.forename: Ichiro
authors.initials: I
authors.lastname: Hiromitsu