MoS 2 and Ni-promoted MoS 2 catalysts supported on γ-Al 2 O 3 , siliceous SBA-15, and Zr-and Ti-modified SBA-15 were explored for the simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and hydrodenitrogenation (HDN) of o-propylaniline (OPA). In all cases, OPA reacted preferentially via initial hydrogenation, and DBT was converted through direct sulfur removal. HDN and HDS activities of MoS 2 catalysts are determined by the dispersion of the sulfide phase. Ni promotion increased its dispersion and activity for DBT HDS and also increased the rate of HDN via enhancing the rate of hydrogenation. On nonpromoted MoS 2 catalysts, HDS was strongly inhibited by NH 3 , and the addition of Ni dramatically reduced this inhibiting effect. The conclusion is that HDS is proportional to the concentration of Mo and Ni on the edges of sulfide particles. In contrast, the direct hydrodenitrogenation of OPA occurs only on accessible Mo cations and, hence, decreases with increasing Ni substitution. The nature of the support influences the dispersion of the nonpromoted catalysts as well as the decoration degree of Ni on the edges of the Ni−Mo−S phase. Furthermore, the acidity of the support influences the acidity of the supported sulfide phase, which may play an important role in HDN.

No abstract

The chemical composition and structure of NiMo sulfides supported on γ‐Al2O3 and its properties for hydrogenation of polyaromatic compounds is explored. The presence of Ni favors the formation of disperse octahedrally coordinated Mo in the oxide precursors and facilitates its reduction during sulfidation. This decreases the particle size of MoS2 (measured by transmission electron microscopy) and increases the concentration of active sites up to a Ni/(Mo+Ni) atomic ratio of 0.33. At higher Ni loadings, the size of the MoS2 did not decrease further, although the concentration of adsorption sites and accessible Ni atoms decreased. This is attributed to the formation of NiSx clusters at the edges of MoS2. Nickel also interacts with the support, forming separated NiSx clusters, and is partially incorporated into the γ‐Al2O3, forming a Ni‐spinel. The hydrogenation of phenanthrene follows two pathways; by adding one or two H2 molecules, 9,10‐dihydrophenanthrene or 1,2,3,4‐tetrahydrophenanthrene are formed as primary products. Only symmetric hydrogenation, leading to 9,10‐dihydrophenanthrene, was observed on unpromoted MoS2/γ‐Al2O3. In contrast, symmetric and deep hydrogenation (leading to 9,10‐dihydrophenanthrene and 1,2,3,4‐tetrahydrophenanthrene, respectively) occur with similar selectivity on Ni‐promoted MoS2/γ‐Al2O3. The rates of both pathways increase linearly with the concentration of Ni atoms in the catalyst. The higher rates for symmetric hydrogenation are attributed to increasing concentrations of reactive species at the surface, and deep hydrogenation is concluded to be catalyzed by Ni at the edge of MoS2 slabs.

Supported MoS2/γ‐Al2O3 and Ni‐MoS2/γ‐Al2O3 as well as unsupported Ni‐MoS2 were investigated in the hydrodenitrogenation (HDN) of quinoline in the presence of dibenzothiophene (DBT). The supported oxide catalyst precursors had a well‐dispersed amorphous polymolybdate structure that led to the formation of a highly dispersed sulfide phase. In contrast, the unsupported catalyst precursor consisted of a mixture of nickel molybdate and ammonium nickel molybdate phases that formed stacked sulfide slabs after sulfidation. On all catalysts, the reaction pathway for the removal of N in quinoline HDN mainly followed the sequence quinoline→1,2,3,4‐tetrahydroquinoline→decahydroquinoline→propylcyclohexylamine→propylcyclohexene→propylcyclohexane. The hydrodesulfurization of DBT proceeded mainly by direct desulfurization towards biphenyl. For both processes, the activity increased in the order MoS2/γ‐Al2O3

No abstract