Vol 57, No 14 (2017)

The review concerns recent progress in the design and synthesis of encapsulated nanomaterials based on Group VIII base metals useful for energy and environmental catalysis, including syngas conversion, CO₂ dry reforming, steam reforming, methane conversion, and NH₃ decomposition, as well as other nanocatalytic processes, for example, electrochemical synthesis. Catalysts with various encapsulated structures (core@shell, yolk@shell, core@tube, mesoporous, and layered structures) are described. The performance of encapsulated structures in catalytic reactions, including protection of metal nanoparticles from sintering which is favorable for activity preservation owing to the confinement effect and intensification of processes by multifunctional catalysts, is discussed. Prospects for application of encapsulated materials are analyzed.

The activity of supported and in situ synthesized sulfide Ni–W catalysts based on a low-silicon zeolite Y (SiO₂/Al₂O₃ = 5.2) in the hydrocracking of vacuum gas oil is studied. It is shown that the temperature and time of reaction affect the fractional composition and the sulfur content in conversion products. It is found that the phase of tungsten sulfide as well as the mixed Ni−W−S phase active in hydrogenation are formed on the catalyst surface. It is proposed that an increase in activity for the in situ formed catalyst may be explained by a high content of sulfide phases on the catalyst surface and accessibility of the zeolite pore system.

The hydrodearomatization and hydrodesulfurization of the coking resin fraction (below 360°C) in the presence of in situ synthesized Ni–W–S catalysts are studied using tungsten hexacarbonyl W(CO)₆ and nickel(II) 2-ethylhexanoate Ni(C₇H₁₅COO)₂ oil-soluble salts at a molar ratio of W: Ni = 1: 2 as precursors for the Ni–W–S catalysts. The resulting catalysts are characterized by transmission electron microscopy; the formation of agglomerates of nanoparticles with an average diameter of 100–200 nm is shown. The optimum temperature for the hydrotreating of the coking resin (380°C) is determined.

The formation of nanosized stable iron-containing suspensions for implementing Fischer–Tropsch synthesis in the three-phase system is studied. The introduction of a polymer component in the composition of the dispersion medium is favorable for formation of particles of the dispersed phase of catalytic suspension with a size of nearly 170 nm. It is shown that the concentration of polyacrylonitrile in the composite metal-polymer systems affects their catalytic and physicochemical properties. Optimization of the catalyst system composition with respect to the content of the polymer component in the dispersion medium makes it possible to increase the yield of target products of Fischer–Tropsch synthesis in the studied temperature range by 30−35% compared with the system synthesized without any polymer component.