The presence of Na in Ni-promoted MoS₂ provides an interesting case study as Na gets inadvertently incorporated during the reverse micelle synthesis of the nanocatalyst. The effect of Na in Ni-promoted MoS₂ during hydrodesulfurization (HDS) of dibenzothiophene (DBT) is investigated here through combined experiment and density functional theory (DFT) studies. Computations suggest that Na replaces otherwise more HDS active Ni sites, which are likely to be present as metal atoms on S edge or on metallic edge sites of MoS₂(100). The presence of Na dopant instead of Ni results in the molecular hydrogen dissociation step becoming more endothermic, leading to the lowering of HDS catalytic activity. The HDS of DBT decreases with an increase of Na concentration in Ni-promoted MoS₂. However, the concentration of Na has a nonmonotonic effect on the selectivity of different mechanistic pathways of HDS. The selectivity toward a cost-effective direct desulfurization (DDS) pathway increases up to an optimal Na concentration, after which the selectivity decreases as observed from experiments and corroborated by DFT studies. However, DDS selectivity always remains higher, which is the critical feature of Na incorporation in Ni-promoted MoS₂.

中文翻译：

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钠对Ni促进的MoS ₂加氢脱硫反应的影响：联合实验与模拟研究

在Ni促进的MoS ₂中Na的存在提供了一个有趣的案例研究，因为在纳米胶束的逆胶束合成过程中无意中掺入了Na。本文通过结合实验和密度泛函理论（DFT）研究了Na在Ni促进的MoS ₂中的二苯并噻吩（DBT）加氢脱硫（HDS）过程中的作用。计算表明，Na替代了更多的HDS活性Ni位，这些位可能以金属原子的形式出现在MoS _2的S边缘或金属边缘上（100）。Na掺杂剂而不是Ni的存在会导致分子氢解离步骤变得更加吸热，从而导致HDS催化活性降低。在Ni促进的MoS _2中，DBT的HDS随着Na浓度的增加而降低。但是，Na的浓度对HDS不同机理途径的选择性具有非单调影响。对具有成本效益的直接脱硫（DDS）途径的选择性增加，直至达到最佳的Na浓度，此后，如实验观察到的并经DFT研究证实，选择性降低。但是，DDS的选择性始终保持较高，这是在Ni促进的MoS ₂中Na掺入的关键特征。