Bifunctional MoS₂-Silica-Alumina Catalysts for Slurry Phase Phenanthrene-Decalin Hydroconversion

Abstract

MoS2-amorphous silica-alumina (MoS2-ASA) bifunctional catalysts for slurry-phase hydroconversion of the model reactants phenanthrene and decalin were prepared using three distinct methodologies. The MoS2-ASA catalysts were prepared by (i) a mechanical mixture of MoS2 (prepared separately) and ASA, which were mixed directly in the reactor for the hydroconversion test (MM catalyst); (ii) in situ sulfidation of the molybdenum precursor in the presence of the ASA, both dispersed in the phenanthrene-decalin reaction mixture (IS catalysts); and (iii) impregnation of molybdenum octoate onto ASA, followed by thermal treatment to chemically link the Mo precursor to the ASA surface followed by sulfidation prior to the catalytic test (IMP catalyst). Among the three preparation methods, the MoS2-ASA catalysts prepared in situ (IS) had the highest MoS2 dispersion and degree of sulfidation and yielded the highest hydrogenating activity at the lowest Mo catalyst content (2.9Mo-ASA). Although the MoS2 blocked Brønsted acid sites decreasing the ASA acidity, especially in IS and IMP catalysts, at the low Mo concentrations required with the IS methodology, most of the acidity was retained. In addition, in the case of IS catalysts, MoS2 particles were also found dispersed in the slurry feed independently of the ASA. Consequently, the IS catalyst retained the advantages of the unsupported MoS2 with the additional functionality of the acid component of the bifunctional catalyst; hence, conversion was promoted due to both hydrogenation and hydrocracking reactions. These observations suggested that the bifunctional MoS2-ASA catalysts prepared in situ promotes hydrocracking reactions at lower temperatures reducing the severity of reaction conditions and limiting coke formation in slurry-phase hydroconversion.

Slurry-Phase Hydrocracking of a Decalin–Phenanthrene Mixture by MoS2/SiO2–ZrO2 Bifunctional Catalysts

“…According to Sanchez et al, they can be divided into seven groups: (1) C 10 −C 12 AROalkylmonoaromatics and alkyl-diaromatics mainly comprising alkyl-benzenes, alkyl-indanes, alkyl-tetralines, and alkyl-naphthalenes; (2) C 10 ISOskeletal isomerization products of decalin mainly comprising alkyl-dinaphthenes; (3) C 10 RO ring-opening products of decalin mainly comprising alkylcyclohexanes and alkyl-cyclopentanes; (4) C 7 −C 9 cracking products mainly comprising alkyl-cyclopentanes and alkylcyclohexanes; (5) C 14 HYDhydrogenation products of phenanthrene mainly comprising dihydrophenanthrenes, tetrahydrophenanthrenes, octahydrophenanthrenes, and perhydrophenanthrenes; (6) C 14 ROring-opening products of phenanthrene mainly comprising alkyl-diaromatics; and (7) C 14 + combination products mainly comprising alkyl phenanthrenes and alkyl-benzyl-benzenes. 19 The detailed structural information about these products is presented in the Supporting Information (see Figure S1). The selectivity (S i ) and yield (Y i ) of each product group were calculated using the following equations…”

“…It has been demonstrated in the previous literature that Brønsted acid sites are necessary for the conversion of decalin, which is subject to a β-fracture mechanism with isomerization taking place first followed by ring opening and cracking. 19,36 On the other hand, Brønsted acid sites can promote the ringopening reactions of phenanthrene. 37 Thus, catalysts with more Brønsted acid sites are more favorable for the catalytic conversion of decalin and phenanthrene.…”

“…Additionally, mixed metal oxides have high thermal stability, and the number and strength of acid sites can be more easily adjusted. Meanwhile, mixed metal oxides with nanosized particles and large surface areas can be more easily prepared by simple methods. − Among various mixed metal oxides, amorphous SiO 2 –Al 2 O 3 mixed oxides are commonly used ones for slurry-phase hydrocracking. − New Brønsted acid sites can be formed at Si–O–Al bridge bonds through the interaction between the two oxides. These Brønsted acid sites are very favorable for the hydrocracking reaction.…”

Slurry-Phase Hydrocracking of Heavy Oil with Bifunctional Catalysts In Situ Generated from Oil-Soluble Ionic Liquid and Mixed Metal Oxide

“…The cracking reactions are promoted by thermal cracking; therefore, the slurry-phase hydrocracking should be performed at high temperatures. To address this issue, researchers proposed to combine nanosized transition metal sulfides and metal oxides to formulate bifunctional catalysts for slurry-phase hydrocracking. , Within such bifunctional catalysts, the nanosized transition metal sulfides are in situ generated from oil-soluble precursors and provide active sites for hydrogenation reactions. The metal oxides are presynthesized with abundant acidic sites and provide active sites for cracking reactions.…”