New insights into the formation of bulk NiMo hydrotreating catalysts: Influence of the Ni/Mo molar ratio

Abstract

A series of granular NiMo bulk catalysts with Ni/Mo molar ratio – 0.5–2.0, and alumina as a binder was prepared by the spray drying of Ni-Mo-citrate solution followed by calcination, plasticizing and granulation. The samples were characterized by a variety of techniques (N₂ physisorption, XRD, UV–vis DRS, IR spectroscopy, STEM, EDS and XPS). The catalytic activity was evaluated in the hydrotreating of SRVGO, carried out in a fixed bed reactor at P = 5.0 MPa, volume ratio H₂/SRVGO = 600 Nm³/m³, WHSV = 1.5 h⁻¹, T₁ = 360 °C, T₂ = 380 °C. The investigation techniques data show that the catalysts with low Ni/Mo molar ratio contain amorphous phases, AlOOH and crystal NiMoO₄. After sulfiding, it results in the formation of bulk spherical particles of MoS₂ and some MoS₂ being distributed over alumina binder in sulfide catalysts. Ni is distributed on the inner part of the formed MoS₂ or as NiMoS phase. When Ni content increases, the catalysts mostly contain amorphous Ni-Mo phase and some crystallite Mo-containing phase (Ni/Mo molar ratio of 2), spherical particles lose their «correct» spherical shape and Ni particles become much bigger. It also leads to the collapse of catalyst’s texture. XPS data show correlation between Ni^NiMoS/Mo⁴⁺ and rate constant of HDS reactions. According to residual S content, the highest HDS volume activity was observed for the catalyst with Ni/Mo molar ratio of 1/1 at both process temperatures. The values of residual N content correlate well with residual S content in hydrotreating products.