Influence of the composition and morphology of nanosized transition metal sulfides prepared using the Anderson-type heteropoly compounds [X(OH)6Mo6O18] n− (X = Co, Ni, Mn, Zn) and [Co2Mo10O38H4]6− on their catalytic properties

Abstract

Using the Anderson-type heteropoly compounds (HPCs) [X(OH)6Mo6O18]n− (X = Co, Ni, Mn, Zn) and [Co2Mo10O38H4]6− and cobalt (or nickel) nitrate, XMo/Al2O3 and Co(Ni)-XMo/Al2O3 catalysts were prepared. The catalysts were studied by low-temperature nitrogen adsorption, X-ray diffraction, and high-resolution transmission electron microscopy. The average length of the active-phase particles of the catalysts was 3.5 to 3.9 nm, and the average number of MoS2 layers in a packet was 1.4 to 2.1. The catalytic properties of the samples, which were estimated in dibenzothiophene (DBT) hydrodesulfurization and in the hydrotreating of the diesel fraction, are considerably dependent upon both the type and composition of the HPC, and the nature of the applied promoter (Ni or Co). As compared to the Ni-promoted catalysts, the Co-promoted samples exhibit a higher desulfurization activity, whereas the hydrogenation ability of the Ni-XMo/Al2O3 catalysts surpasses that of the Co-XMo/Al2O3 ones. The catalytic properties depend on the morphology of the nanostructured active phase. With a growing number of MoS2 layers in the packet of the catalysts’ active phase, the DBT hydrodesulfurization rate constants for both the direct desulfurization route and the preliminary hydrogenation rote rise linearly and the selectivity falls linearly for the hydrogenation route. The selectivity of Ni-XMo/Al2O3 decreases to a greater extent than that of Co-XMo/Al2O3. The dependences of the catalytic properties on the morphology of the catalysts’ active phase are consistent with the “dynamic” model of the functioning of the active sites of transition metal sulfides.