Active Sites on Nickel‐Promoted Transition‐Metal Sulfides That Catalyze Hydrogenation of Aromatic Compounds

Abstract

Hydrogenation on Mo and Wsulfides occurs at the edges of the sulfide slabs.T he rate of hydrogen addition is directly proportional to the concentration of sulfhydryl (SH) groups at the slab edge and the metal atom attached to it. Sulfhydryl groups vicinal to edge-incorporated Ni hydrogenate with muchh igher rates than SH close to Mo and W. Each subset of SH groups,however,exhibits nearly identical intrinsic activity and selectivity,independent of the sulfide composition. The higher activity of Ni-WS 2 compared to Ni-MoS 2 stems from ah igher concentration of SH groups on the former sulfide associated with ah igher tendency of its surface vacancies to react with H 2 .

Enhancing hydrogenation activity of Ni-Mo sulfide hydrodesulfurization catalysts

“…These cleaned mixed sulfides also allow us to relate nature and concentration of active sites to catalytic properties and to corroborate recent insight into active sites (11).…”

“…We surmise that these are a fraction of CUS in NiS x . The direct proportionality suggests a fixed ratio between CUS and SH sites in the treated samples, as we have also observed with supported sulfide catalysts (11). Therefore, we used the CUS concentration (half of NO uptake) as a quantity for the concentration of active sites in the studied materials while noting that some of the CUS from nonpromoted sites contribute only to a minor extent to DDS and HYD activities.…”

Maximizing Active Site Concentrations at Ni-Substituted WS2Edges for Hydrogenation of Aromatic Molecules

“…25−27 Figure 1 shows the rate of reaction of Phe hydrogenation as a function of the measured atomic Ni/(Ni + W) ratio (bulk) for the parent and the acidtreated series of materials. The variation of the Phe conversion with residence time is shown in Figure S3 for the acid-treated (Ni)WS 2 /γ-Al 2 O 3 catalysts (plots for the parent catalysts are shown elsewhere 25 ), and the corresponding reaction rates are listed in Table S3. Hydrogenation of Phe produces 9,10dihydrophenanthrene (DiHPhe) and 1,2,3,4-tetrahydrophenanthrene (TetHPhe) as primary products, while 1,2,3,4,5,6,7,8-octahydrophenanthrene (symOHPhe) and 1,2,3,4,4a,9,10,10a-octahydrophenanthrene (asymOHPhe) are secondary products.…”

“…Hydrogenation of Phe produces 9,10dihydrophenanthrene (DiHPhe) and 1,2,3,4-tetrahydrophenanthrene (TetHPhe) as primary products, while 1,2,3,4,5,6,7,8-octahydrophenanthrene (symOHPhe) and 1,2,3,4,4a,9,10,10a-octahydrophenanthrene (asymOHPhe) are secondary products. A simplified reaction network under these conditions comprises two parallel routes, 23,25 i.e., initial hydrogenation of the middle ring (Phe → DiHPhe → asymOHPhe) and initial hydrogenation of a lateral ring (Phe → TetHPhe → symOHPhe), and the rates of these two routes are denoted r 1 and r 2 , respectively. The r 1 :r 2 ratio was 4:1 on WS 2 /γ-Al 2 O 3 -a and 1:1 to 1:1.7 on Ni(x)WS 2 /γ-Al 2 O 3 -a and -b catalysts (Table S3).…”

“…These observations are in agreement with those reported for (Ni)MoS 2 /γ-Al 2 O 3 23 and parent (Ni)WS 2 /γ-Al 2 O 3 . 25 The yields and selectivities of the products as a function of Phe conversion are shown in Figures S4 and S5. On WS 2 /γ-Al 2 O 3 -a, secondary products were not detected at <10% conversions.…”