Home – Home – Jornals – Chemistry for Sustainable Development 2015 number 6

Results of the analysis of monographs, papers and patents dealing with the studies of physicochemical and catalytic properties of the catalysts of petroleum processing synthesized with the help of mechanical activation are presented. The results of Russian and foreign studies in the area of changes in the efficiency of catalyst performance in the case if intense mechanical load is involved in the technological process of catalyst synthesis.

The effect of modification of sulphated zirconium dioxide by aluminium oxide additives on its texture, phase composition, acidity and catalytic properties in the process of isobutane alkylation with butanes was studied. It is shown that the best catalytic properties are those of the SO₄^2-−ZrO₂−Al₂О₃ sample with aluminium oxide content 20 mass %, annealed at a temperature of 650 °C.

Pd/Sibunit catalysts with palladium content 1 and 1.5 % were studied in aqua-phase hydrogenation of furfurol at different temperatures (323 and 363 K) and hydrogen pressure (0.5 and 2.0 MPa). The sample with palladium content 1.5 % exhibited activity in the studied reaction only at a temperature of 363 K. Under rigid reaction conditions (363 K, 2.0 MPa) the catalyst 1.5 % Pd/Sibunit has advantages over the samples based on carbon nanotubes (CNT) and technical-grade carbon (TC): it is more active than 1.5 % Pd/TC in furfurol transformation (transformation degree 96 %) and is highly selective (76 %) in the formation of furfuryl alcohol in comparison with 1.5 % Pd/CNT, with close degrees of furfurol transformation. A decrease in palladium content in the sample did not lead to worsening of the catalytic characteristics in the studied reaction under the most rigid reaction conditions. The degree of furfurol transformation on the sample 1 % Pd/Sibunit (91 %) turned out to be higher than that with the catalyst 1.5 % Pd/TC, while in the selectivity of the formation of furfuryl alcohol (77 %) it exceeded the sample 1.5 % Pd/CNT substantially.

Acidity of a series of the samples of borate-containing aluminium oxide with B₂O₃ content 0.9 to 27.5 mass % used as a support for the catalysts of hydrocarbon hydroisomerization was studied by means of probe EPR spectroscopy. On the basis of the data on the interaction of probe molecule TEMPO with acidic centres, it was established that Lewis acidity decreases with an increase in B₂O₃ content from 0.9 to 13.9 mass %, while for the samples with 17.3 and 27.5 mass % B₂O₃ exclusively Brønsted acidity is manifested. It is demonstrated that the number of Brønsted acidic centres of medium strength, determined with the help of anthracene molecule as an EPR probe, increases with an increase in B₂O₃ content for the whole series of the studied oxide systems.

Effect of the concentration of hydrogenising component of Pt/B₂O₃−Al₂O₃ catalysts on the yield and composition of diesel fractions formed during one-stage hydrocracking of sunflower-seed oil at a temperature of 400 and 350 °C, pressure 4.0 MPa, mass rates of raw material input 5.0 and 1.0 h^-1 was studied. It was established by means of TPR-Н₂, IR spectroscopy of adsorbed СО and ESDR that the hydrogenating component of the catalysts is represented by the particles of metal platinum Pt ⁰. Catalytic systems with metal content 0.3−1.0 mass % provide complete hydrodeoxygenation of oil and the maximal yield of the diesel fraction as a result of decarboxylation, hydrodecarbonylation and "reduction" proceeding on them. The major components of diesel fractions obtained with these systems at a temperature of 350 °C and mass rate of raw material input 1.0 h^-1 are n -alkanes С₁₅−С₁₈. Diesel fractions formed in the presence of the indicated systems at a temperature of 400 °C and mass rate of raw material input 5.0 h^-1 in addition to n- alkanes also include isoalkanes and cycloalkanes (up to 40 mass %). As a result of hydrocracking of oil on the catalyst with Pt content of 0.5 mass % for 20 h at a temperature of 400 °C and mass rate of raw material input 1.0 h^-1, diesel fraction with the yield not less than 82.0 mass % and mass fraction of isoalkanes not less than 76.1 % was obtained.

The effect of nickel and rhenium content in the system NiO−Re₂O₇/B₂O₃−Al₂O₃ on catalyst activity and selectivity in the process of single-stage synthesis of propylene from ethylene was studied. It was established that Ni and Re content in the catalyst which is optimal from the viewpoint of selectivity is 5 mass % per each metal (calculated for NiO and Re₂O₇). On the basis of the data of physicochemical methods (XPA, IR of hydroxyl coating, IR of adsorbed CO, ESDR) it is demonstrated that the precursors of nickel and rhenium interact at the stage of synthesis with the support forming active ionic forms of nickel and rhenium-containing compounds strongly fixed on the surface.

Effect of the addition of zirconium oxide on the structural and catalytic properties of MnO_x−Al₂O₃ in CO oxidation was studied. It was established that the addition of zirconium oxide (5 and 10 mol. % calculated for the metal) into MnO_x−Al₂O₃ stabilizes the structure of γ-Al₂O₃, preventing its transformation into corundum with an increase in annealing temperature, and promotes the formation of spinel Mn_3-xAl_xO₄, which is not typical for the system MnO_x−Al₂O₃ annealed in the air. At the same time, the tetragonal modification of ZrO₂ gets stabilized at high Al₂O₃ content, which is characteristic of binary systems. Two maximal are observed on the curve of the dependence of catalytic activity of the system MnO_x−ZrO₂−Al₂O₃ on the temperature of preliminary annealing; these maxima are likely to be connected with structural transformations in the system with an increase in annealing temperature. The mutual effect of ZrO₂ and Al₂O₃ in the system MnO_x−ZrO₂−Al₂O₃ leads to the shift of the maxima of catalytic activity to higher temperature region with respect to binary systems MnO_x−ZrO₂ and MnO_x−Al₂O₃.

Thermochemical stability of the carbonaceous support Sibunit in the catalysts of low-temperature synthesis of ammonia Ru/Sibunit and Ru−Cs/Sibunit was studied. For Ru and Ru−Cs samples, the curves of temperature-programmed reduction (methanation) were obtained. It was shown that for non-promoted catalysts methane formation starts at 350 °C, while for Ru−Cs/Sibunit the start of СН₄ formation shifts to higher temperatures, while the amount of formed methane decreases during experiment. On the basis of the data obtained, an assumption concerning the role of cesium oxide in the inhibition of methanation process is made.

Effect of methane/platinum ratio on the adsorption properties of alumoplatinum catalyst is considered. The degree of methane dehydrogenation on Pt/Al₂O₃ surface is calculated for the whole range of studied СН₄/Pt ratios. The reactivity of adsorbed forms of methane in the formation of C−C bond during the joint transformation with n-pentane and the formation of aromatic hydrocarbons was discovered.

Effect of the nature of the inert component of the gas phase (argon, nitrogen, helium) on the morphological features of deposited carbon during methane pyrolysis on the resistive catalyst (Fechral coil heated with electric current) was studied. It was shown that fibrous carbon in the form of multiplayer tubes is formed on Fechral surface during the catalytic pyrolysis of methane in mixture with argon at a temperature ≥1050 °C, Both ordered carbon fibres of different diameters with a metal particle situated at the end of the fibre and dispersed carbon deposited from the gas phase are observed in reactor walls. In methane-nitrogen mixture, carbon fibre obtained on Fechral surface is composed of oval formations; each of them consists of narrowing and broadening concentric carbon layers embedded into each other. Carbon fibres formed in helium are distinguished by less defective surface and the smallest diameter in comparison with the fibres obtained in argon and in nitrogen. It is stressed that the growth of carbon fibres proceeds mainly into the space between the coils along which the current passes into different directions.

The problems connected with the effect of the composition of mechanically activated mixture and the modes of mechanical activation on the change of composition and structure of porous inorganic materials - supports for the catalysts of petroleum processing are considered. Results of the studies are reported, aimed at an increase in the efficiency of the performance of catalysts for petroleum processing with the supports synthesized under the conditions of intense mechanical action.