Ni–Mo sulfide nanosized catalysts from water-soluble precursors for hydrogenation of aromatics under water gas shift conditions

Abstract

<jats:title>Abstract</jats:title><jats:p>The unsupported catalysts were obtained during hydrogenation by in situ high-temperature decomposition (above 300 °C) of water-soluble metal precursors (ammonium molybdate and nickel nitrate) in water-in-oil (W/O) emulsions stabilized by surfactant (SPAN-80) using elemental sulfur as sulfiding agent. These self-assembly Ni–Mo sulfide nanosized catalysts were tested in hydrogenation of aromatics under CO pressure in water-containing media for hydrogen generation through a water gas shift reaction (WGSR). The composition of the catalysts was determined by XRF and active sulfide phase was revealed by XRD, TEM and XPS techniques. The calculations based on TEM and XPS data showed that the catalysts are highly dispersed. The surfactant was found to affect both dispersion and metal distribution for Ni and Mo species, providing shorter slab length in terms of sulfide particle formation and stacking within high content of NiMoS phase. Catalytic evaluation in hydrogenation of aromatics was performed in a high-pressure batch reactor at <jats:italic>T</jats:italic> = 380–420 °С, p(CO) = 5 MPa with water content of 20 wt.% and CO/H<jats:sub>2</jats:sub>O molar ratio of 1.8 for 4–8 h. As shown experimentally with unsupported Ni–Mo sulfide catalysts, the activity of aromatic rings depends on the substituent therein and decreases as follows: anthracene&gt;&gt;1-methylnaphthalene≈2-methylnaphthalene&gt;1,8-dimethylnaphthale-ne&gt;&gt;1,3-di-methylnaphthalene&gt;2,6-dimethylnaphthalene≈2,3-dimethylnaphthalene&gt;2-ethyl-naphthalene. The anthracene conversion reaches up to 97–100% for 4 h over the whole temperature range, while for 1MN and 2MN it doesn’t exceed 92 and 86% respectively even at 420 °С for 8 h. Among dimethyl-substituted aromatics the higher conversion of 45% was achieved for 1,8-dimethylnaphthalene with 100% selectivity to tetralines at 400 °С for 6 h. Similar to 1- and 2-methylnaphtalenes, the hydrogenation of asymmetric dimethyl-substituted substrate carries out through the unsubstituted aromatic ring indicating that steric factors influence on the sorption mechanism over active metal sites. The catalysts were found to be reused for at least six cycles when the hydrogenation is sulfur-assisted preventing metal oxide formation. It was established, that at the first 2–3 h known as the induction period, the oxide catalyst precursors formed slowly by metal salt decomposition, which reveals that it is the rate-determining step. The sulfidation is rather fast based on high catalytic activity data on 2MN conversion retaining at 93–95% upon recycling.</jats:p>

Biphenyl Hydrogenation with Syngas for Hydrogen Purification and Transportation: Performance of Dispersed Catalytic Systems Based on Transition Metal Sulfides

“…Such systems are resistant to СО, which allows the hydrogenation to be performed in the СО-water system using hydrogen formed in situ by the reaction of CO with H 2 O. Both supported catalysts [28] and dispersions of nanosized sulfides of the corresponding metals [29,30] can be used in the process. The advantages of the unsupported dispersed catalysts are high specific surface area, high content of the active components, and resistance to catalytic poisons.…”

“…The advantages of the unsupported dispersed catalysts are high specific surface area, high content of the active components, and resistance to catalytic poisons. In addition, the unsupported catalytic systems can be prepared in situ by high-temperature decomposition of oil-soluble metal salts in the presence of a sulfidizing agent precursor (elemental sulfur) and remain stable in the presence of large amounts of water [29][30][31][32].…”

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

“…Slurry-phase hydrocracking catalysts have been developed by a combination of ultradispersed MoS 2 with an acidic component (an amorphous silica–alumina, among others) in the range of 0.1–10 wt %. , Usually, the MoS 2 phase is obtained in situ during the catalytic reaction due to the advantages in the structure and morphology of unsupported transition metal sulfides compared to conventional supported MoS 2 catalysts. − We have reported on the improved performance of ultradispersed bifunctional hydrocracking catalysts obtained by the in situ formation of MoS 2 in the presence of amorphous silica–alumina . The positive effect of combining MoS 2 with a low acidity component (i.e., SiO 2 –ZrO 2 mixed oxides) was recently confirmed by Ma et al …”