Molybdenum-sulfide particles inside NaY zeolite as a hydrotreating catalyst prepared by adsorption of Mo(CO)6 Original Research Article

NaY zeolite is used as support for optimal dispersed molybdenum-sulfide to study the effect of dispersion on the thiophene HDS. Two molecules Mo(CO)6 are deposited inside the supercages of NaY by both a static as well as a flow type preparation method. During deposition inside the supercages by the flow method 1–1.5 CO ligand per Mo atom is removed. For the formation of Mo-sulfide particles in the zeolite cavities the sulfidation has to be carried out in the absence of water. Once the Mo sulfide particles are formed in the pores in this way, treatment with H2O or NH3 does not change the catalytic activity. In contrast herewith, the activity strongly decreases when the sulfidation is carried out with humidified H2S due to the formation of well-structured MoS2 at the external zeolite surface. The NaY supported molybdenum-sulfide samples are characterized by EXAFS, AAS, XRD and TEM measurements.According to EXAFS, after stepwise sulfidation of Mo(CO)4.5–5/NaY up to 773 K small Mo-sulfide species are formed inside the NaY supercages consisting of two Mo atoms with RMo–Mo=3.16 Å (like in MoS2) surrounded by S and denoted by ‘Mo(3.16 Å)Sx’. The formation of these dimer species inside the zeolite supercages takes place via the intermediate formation of the dimer ‘Mo(2.78 Å)Sx’ species with RMo–Mo=2.78 Å (like in MoS3). In all the formed Mo-sulfide species also some additional light atoms are contributing to the Mo radial distribution function. However, these atoms could not be identified in an unambiguous way and, hence, troubled an easy straight forward analysis of the EXAFS data as will be described.