posted on 2021-01-21, 18:04authored bySharda Mundotiya, Rupesh Singh, Sulay Saha, Rohit Kakkar, Sachin Pal, Deepak Kunzru, Raj Ganesh S. Pala, Sri Sivakumar
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.