Bifunctionality of a MoS₂-Amorphous Silica–Alumina-Dispersed Catalyst for Slurry-Phase Hydroconversion: Effect of Acid and Hydrogenating Site Ratios

Abstract

To achieve maximum yield from bifunctional catalysts in slurry-phase hydrocracking of heavy oil, an appropriate balance between the acidic and hydrogenating functions of the catalyst is required. In this study, the bifunctional behavior of MoS2-amorphous silica–alumina (ASA) catalysts was investigated by varying the number of Brønsted acid sites (ηH+) and MoS2 edge sites (ηMo) associated with ASA and MoS2, respectively. Using a model feed consisting of phenanthrene and decalin, we report evidence of bifunctional catalysis for MoS2-ASA catalysts with ηH+/ηMo ratios between 3.1 and 15.5. Deviations from bifunctional behavior were also observed: at a low ηH+/ηMo ratio (0.39), phenanthrene hydrogenation was preferred, whereas at the highest ηH+/ηMo ratio (30.9), acid-catalyzed reactions dominated and promoted coke formation that resulted in catalyst deactivation. Considering that the in situ formation of MoS2 blocked some acid sites on the ASA, we introduced a new parameter that quantified the number of Brønsted acid sites available in the reactor system (ηH+ c). We show that the total product yield correlated with ηH+ c and that the maximum yield occurred for the catalyst with the highest ηH+ c.

Detailed understanding on thermodynamic and kinetic features of phenanthrene hydroprocessing on Ni‐Mo/HY catalyst

“…Moreover, due to the low cost and abundant resources, transition metal catalysts are suitable for large‐scale application in industry. However, the activity and selectivity of transition metal catalysts are lower than those of noble metal catalysts 17–20 . To enhancing the activity and selectivity of transition metal catalysts, many studies have been devoted to observe the behaviors of transition metal catalysts in the hydrogenation of polyaromatic hydrocarbons 17–20 .…”

“…To enhancing the activity and selectivity of transition metal catalysts, many studies have been devoted to observe the behaviors of transition metal catalysts in the hydrogenation of polyaromatic hydrocarbons 17–20 . Sánchez et al found that, on a MoS 2 ‐amorphous silica‐alumina catalyst, at a ratio of Brønsted acid site number (ηH + ) to MoS 2 edge site number (ηMo) (ηH + /ηMo) of 0.39, phenanthrene hydrogenation was preferred, whereas at a ηH + /ηMo ratio of 30.9, acid‐catalyzed reactions, and coke formation were dominated 18 . Restrepo‐Garcia et al reported that the selective hydrogenation of the central ring of phenanthrene was enhanced on the catalyst fabricated by loading sulfurized Fe–W on Al‐modified SBA‐15, and the catalyst with an Al/Si molar ratio of 0.04 had the highest selectivity to produce 9,10‐dihydrophenanthrene 19 .…”

“…Transition metal catalysts exhibit excellent ability in resisting poisons and superior stability in the hydrogenation of polyaromatic hydrocarbons, especially at the high temperatures and pressures widely used for the hydrotreating process of gasoline and diesel in industry. [13][14][15][16][17][18][19][20] Moreover, due to the low cost and abundant resources, transition metal catalysts are suitable for large-scale application in industry. However, the activity and selectivity of transition metal catalysts are lower than those of noble metal catalysts.…”

“…However, the activity and selectivity of transition metal catalysts are lower than those of noble metal catalysts. [17][18][19][20] To enhancing the activity and selectivity of transition metal catalysts, many studies have been devoted to observe the behaviors of transition metal catalysts in the hydrogenation of polyaromatic hydrocarbons. [17][18][19][20] Sánchez et al found that, on a MoS 2 -amorphous silica-alumina catalyst, at a ratio of Brønsted acid site number (ηH + ) to MoS 2 edge site number (ηMo) (ηH + /ηMo) of 0.39, phenanthrene hydrogenation was preferred, whereas at a ηH + /ηMo ratio of 30.9, acid-catalyzed reactions, and coke formation were dominated.…”

“…[17][18][19][20] Sánchez et al found that, on a MoS 2 -amorphous silica-alumina catalyst, at a ratio of Brønsted acid site number (ηH + ) to MoS 2 edge site number (ηMo) (ηH + /ηMo) of 0.39, phenanthrene hydrogenation was preferred, whereas at a ηH + /ηMo ratio of 30.9, acid-catalyzed reactions, and coke formation were dominated. 18 Restrepo-Garcia et al…”