Vol 56, No 6 (2016)

This review is concerned with the analysis of nanoheterogeneous catalysis (catalysis in heterogeneous-dispersed systems with nanosized particles of the dispersed phase) in the hydroconversion of a vacuum distillation residue, hydrogenation of individual aromatic hydrocarbons and technical mixtures, and Fischer–Tropsch synthesis. For nanoheterogeneous catalysis, in addition to factors that are typical for heterogeneous catalysis, important factors are the size effect, the all-round accessibility of catalytically active species to reagents, the absence of a porous structure, a high efficiency of heat transfer in the dispersion medium, and an extremely low mass concentration of the catalyst in the suspension reactor (0.05–0.5%) at a high concentration of nanoparticles per reactor volume unit (10¹³–10¹⁵ particles per cubic centimeter). A fine tuning of catalytic processes may be performed in nanoheterogeneous catalysis via a change in the morphology, size, and structure of nanoparticles and variation in their concentration in a suspension reactor. In many cases, the aggregation of nanoparticles accompanied by the formation of nanoaggregates may become the decisive factor for the final outcome of the test reaction and special efforts are needed to stabilize the suspension of catalytically active particles. Technologies based on catalysis by nanosized particles of the dispersed phase have undergone benchmark and pilot tests and are entering the period of wide implementation in the hydroconversion of oil vacuum distillation residue and partially in the Fischer–Tropsch synthesis.

Nanoheterogeneous catalysts based on ruthenium nanoparticles dispersed in crosslinked dendrimer matrixes with a size of polymer particles of 100–500 nm show high activity in the hydrogenation of aromatic compounds under two-phase conditions. The addition of water to the reaction medium exerts a strong promoting effect on the activity of the catalysts: The turnover frequency increases by a factor of 3–90 depending on the substrate. When bimetallic (PdRu) nanoparticles are incorporated into the catalyst composition, the rate of benzene hydrogenation increases while the rate of transformation of substituted benzenes decreases.

Nickel–tungsten sulfide catalysts for the hydrogenation and hydrodesulfurization of aromatic hydrocarbons are synthesized by the in situ decomposition of thio salts using different methods: the in situ decomposition of a [BMPip]₂Ni(WS₄)₂ precursor in an ionic liquid, the in situ decomposition of a [BMPip]₂Ni(WS₄)₂ precursor in a hydrocarbon feedstock, the in situ breaking of a SPAN-80 surfactant-stabilized suspension of solid Ni/(NH₄)₂WS₄ precursor particles in a hydrocarbon feedstock, and the decomposition of oil-soluble precursors (tungsten hexacarbonyl and nickel(II) 2-ethylhexanoate) in a hydrocarbon feedstock. The resulting catalysts are characterized by X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy; their catalytic activity is studied in a batch reactor using the example of the hydrofining of light cycle oils with different compositions.

Features of Fischer–Tropsch synthesis in the presence of an iron-containing catalyst supported on spherical nanosilica (the average sizes of spherical SiO₂ and iron-containing particles on the silica surface are 250 and 14 nm, respectively) are studied. The catalyst exhibits high activity in the conversion of syngas, viz., 7.6 times higher than the activity of a 20% Fe/silica gel catalyst. A distinctive feature of a catalyst supported on spherical silica is higher selectivity for liquid products, which decreases only slightly with increasing temperature. Reduction characteristics are studied using the temperature-programmed reduction method; the specific surface area is measured and the phase composition of the synthesized catalyst systems is determined by X-ray diffraction analysis.