Influence of Na₂O and its introduction sequence on the hydrodesulfurization performance of Ni-Mo/MCM-41

Na₂O was introduced to NiMo/MCM-41 catalyst precursor by different sequences, and the hydrodesulfurization (HDS) performances of the prepared catalysts were studied by using a model fuel of decalin solution containing 0.8% DBT. The results indicated that the introduction of Na₂O not only facilitated the formation of β-NiMoO₄, leading to decreased dispersion of active species, but also suppressed the reducibility of NiMo/MCM-41 precursor. The coordination states of Mo species were affected by Na₂O introduced by the consecutive impregnation methods. The HDS activity of NiMo/MCM-41 was strongly affected by the Na₂O introduction sequence. For the catalyst in which Na₂O was introduced by a co-impregnation method, both the activities of the hydrogenation pathway (HYD) and direct desulfurization pathway (DDS) were suppressed, resulting in a decrease in the overall HDS activity. Compared with the co-impregnation and the introduction of Na₂O after NiMo active components, the addition of Na₂O before the deposition of these active components showed much less influence on the HYD activity, but significantly enhanced DDS activity of NiMo/MCM-41, thus an improvement in the overall HDS activity was observed. Both the activity and selectivity of the sulfide catalysts can be modified by adapting a proper addition sequence of the alkali-metal oxides, which is an effective way for the modification of HDS catalysts.