Simultaneous tetralin HDA and dibenzothiophene HDS reactions on NiMo bulk sulphide catalysts obtained from mixed oxides

Abstract

NiMo bulk sulphide catalysts were obtained from mixed-oxides. The mixed-oxides were obtained by calcining the as-synthesized lamellar precursor with the so-called ϕ_y structure and (NH₄)H_2xNi_3−x(OH)₂(MoO₄)₂ formula. The corresponding mixed-oxides obtained by calcination were characterized by nitrogen adsorption, XRD, and ICP. Mixtures of α-NiMoO₄ and β-NiMoO₄ were obtained. A batch reactor was used for CS₂/n-hexadecane in situ sulphidation of the mixed-oxides. A mixture of dibenzothiophene and tetralin was used for the liquid phase reaction carried out at 613 K and 70 bar. After the catalytic tests, the bulk sulphide catalysts were characterised by nitrogen physical adsorption, synchrotron light XRD, EXAFS and HR-TEM. The EXAFS simulations are consistent with disordered nickel sulphide particles dispersed in the catalysts. HR-TEM images showed randomly oriented, stacked-layer particles typical of Mo sulphide. The bulk catalysts had larger HDS and HDA activities and selectivities for hydrogenation reactions than alumina supported conventional catalysts containing the same Ni : Mo ratio. A pronounced support effect was observed for both HDS and HDA reactions. The use of the support strongly suppressed both cyclohexylbenzene formation in HDS of DBT and cis-decalin formation in HDA of tetralin. This suggests that similar active sites are involved in the formation of these compounds on the one hand, while another type of site is involved in biphenyl and trans-decalin formation on the other.