Vol 58, No 14 (2018)

The hydroconversion of tars in the presence of in situ synthesized iron-containing catalysts is studied. Water-soluble iron compounds (FeSO₄, Fe(NO₃)₃, Fe(COOCH₃)₂) are used as precursors which are introduced into the processed feedstock in the composition of the aqueous phase of an inverted emulsion. The tests are conducted on a flow hydroconversion unit with a vertical hollow reactor. It is found that the catalytic activity of the Fe-containing precursors which, under hydroconversion conditions, form Fe_1–xS nanosized particles, in particular, from Fe(COOCH₃)₂, is close to the catalytic activity of previously studied nanodispersed MoS₂. A disadvantage of Fe-containing catalysts in situ synthesized from water-soluble iron compounds (FeSO₄, Fe(NO₃)₃, Fe(COOCH₃)₂) is a relatively high yield of condensation products (coke) under hydroconversion conditions.

The hydroconversion of heavy hydrocarbon feedstocks (fuel oil, tar, rubber, polymer waste, natural bitumen) in the presence of an in situ synthesized suspended nanosized molybdenum catalyst (NMC) is studied. The process is run with recycling of a portion of the unconverted residue containing the in situ synthesized NMC particles. To provide the required NMC concentration in the reaction zone, the process is conventionally divided into stages; at each one, a given NMC concentration is provided by the introduction of a certain amount of the catalyst precursor in the form of an aqueous solution of ammonium paramolybdate into the feedstock and the recycling of a portion of the unconverted residue formed at the previous stage which boils above 500°C and contains the NMC. The balance amount of the unconverted residue boiling above 500°C is used to regenerate the catalyst precursor.

Unsupported nickel–molybdenum sulfide hydrogenation catalysts are ex situ synthesized from precursor-aqueous-solution-in-decalin emulsions. A comparative analysis of the activity of the synthesized catalysts and the GO-38 commercial supported catalyst in polymeric petroleum resin hydrogenation is conducted. It is shown that the activity of the synthesized catalysts is higher than the activity of the supported catalyst at an identical concentration of the active metal in the reaction medium. The effect of the type and concentration of the emulsifier on the size of the emulsion droplets and the catalytic activity of the resulting catalyst is studied. It is shown that polymeric petroleum resins can be used instead of synthetic surfactants as an emulsifier in catalyst synthesis. An optimum Mo/Ni ratio (1/0.25) that provides the maximum degree of hydrogenation (100 and 78% for olefinic and aromatic moieties, respectively) is found. Catalyst activity varies only slightly after reuse in two or three runs; further, activity in the hydrogenation of aromatic moieties decreases, while activity in the hydrogenation of double bonds remains unchanged; in this case, the degree of dispersion does not change.

The catalytic activity of palladium-containing nanodiamonds (Pd/ND) is studied in the model reaction of liquid-phase hydrodehalogenation of monohalobenzenes (chlorobenzene, bromobenzene, and iodobenzene) and ortho-, meta-, and para-isomers of dichlorobenzene under mild conditions (Т = 45°С, \({{P}_{{{{{\text{H}}}_{2}}}}}\) = 1 atm). The obtained results are compared with the catalytic behavior of the palladium-containing activated carbon (Pd/C) under identical conditions. It is found that catalyst Pd/ND is more active than Pd/C and is more stable against the poisonous effect of hydrogen halide forming during the reaction. Study of the effect of HCl and NaOH additives on the catalyst activity shows that, in the presence of HCl, poisoning of the catalyst occurs: the rate of reaction decreases; in the presence of NaOH, the catalyst activity grows; the rate of reaction increases as a result of hydrogen chloride neutralization by an alkali. For both catalysts the rate of reaction decreases in the sequence Cl > Br > I for monohalobenzenes and in the sequence para- > ortho- > meta-isomer in the case of dichlorobenzenes. The obtained dependences are explained using the quantum-chemical modeling of substrates of model reactions.

Ru-containing catalysts based on aluminosilicate halloysite nanotubes (HNTs) are synthesized by preliminary functionalization of the support surface by aminopropyltriethoxysilane (APTES) followed by the microwave-assisted deposition of ruthenium to provide the intercalation of metal nanoparticles into the inner space of nanotubes. The composition and structure of the synthesized catalysts are studied by X-ray fluorescent analysis, low-temperature nitrogen adsorption/desorption, transmission electron microscopy, and hydrogen temperature-programmed reduction. The activity of the catalysts in benzene hydrogenation at a temperature of 80°С and a hydrogen pressure of 3 MPa both in the hydrocarbon medium and in the two-phase system with water is studied. It is shown that, in the presence of water, the hydrogenating activity of the catalyst based on modified halloysite nanotubes is considerably higher than that of the sample prepared using the initial halloysite as a support.

Topochemical transformations occurring during the reduction of low-concentrated catalytic dispersions used for Fischer–Tropsch synthesis in a three-phase slurry reactor are investigated. As evidenced by dynamic light scattering and transmission electron microscopy, catalyst systems containing nanoparticles with sizes of 91 and 3 nm, respectively, are formed in systems containing cobalt at concentrations of 5 and 1 wt %. After catalyst activation via the reduction of cobalt-containing particles by hydrogen, the size of the dispersed phase is 2–3 nm regardless of the content of cobalt in the suspension. The study of magnetic properties of suspension samples in situ indicates that metallic cobalt is formed during the process of catalyst activation, as confirmed by X-ray powder diffraction analysis.

Changes in the phase, morphological, and textural properties of silicoaluminophosphates with the AEI structure during crystallization at 150, 170, and 190°С are studied. Using a combination of physicochemical methods, evolution of the solid phase extracted at different steps of synthesis is shown. It is established that at 150°С the microporous phase containing silicon in tetrahedral positions of the framework appears already at the initial stages of crystallization and further nanostructuring of the solid phase is associated with the incorporation of silicon via the SM3 mechanism. At 170°С, crystallization proceeds through formation of the aluminophosphate and aluminosilicate mixed mesoporous composite. The transformation of mixed composite into the microporous crystalline material is accompanied by the incorporation of [SiO₄] isolated tetrahedra into the forming crystalline framework according to the SM2 mechanism; this provides a strong acidity of the material. The intermediate mesoporous semiproduct extracted at the initial stages of synthesis at 190°С is a mixture of disordered aluminophosphate and coarse mesoporous agglomerates; their transformation into silicoaluminophosphate with the AEI structure occurs only upon silica transfer to the liquid phase, and the incorporation of silicon into the AEI crystalline framework proceeds via the SM3 mechanism with the subsequent formation of silicon islands.