Том 58, № 5 (2017)

Ir complexes are important homogeneous catalysts for formic acid (FA) dehydrogenation. This paper reports that the activity of Ir complexes can be greatly improved through the activation by trace amounts of oxygen. After activation the activity of the heterodinuclear Ir–Ru catalyst increased 18-fold whereas for the mononuclear catalyst a 23-fold increase was observed. Oxygen is the key factor for the activation. But an excessive concentration of oxygen has a negative effect on the activity. There is an optimal concentration of H₂O₂ for the activation of Ir complex catalysts in HCOOH dehydrogenation. A very low concentration of oxygen (2.4 × 10^–6 M) is needed for the activation of the heterodinuclear Ir–Ru catalyst while the mononuclear catalyst requires the presence of oxygen in a much higher concentration (290 × 10^–6 M). From the results of the study it can be inferred that the activation of complex catalysts is due to the interplay of chemical and structural changes. These findings may be helpful in the attempts to improve the catalytic activity of homogeneous catalysts, which are widely used in formic acid dehydrogenation, CO₂ reduction and in other processes. In addition, this paper indicates that iridium complexes are excellent catalysts for the direct synthesis of H₂O₂ from the H₂ and O₂.

The expression of pseudo-second-order rate constants (k_X) for cationic nanoparticle (CN) [CTABr/NaX/H₂O, X = Br, Cl, CTABr = cetyltrimethylammonium bromide] catalyzed piperidinolysis-ionized phenyl salicylate (PSa^–), at constant [CTABr]_T, 0.1 M piperidine (Pip), and 35°C, were calculated from the relationship: k_obs = (k₀ + k_X[NaX])/(1 + K^X/S[NaX]), in which k₀, k_X, and K^X/S are constant kinetic parameters and k_obs represents the pseudo-first-order rate constant for Pip reaction with phenyl salicylate ion in the presence of CN. The source of the large catalytic effect of CN catalyst was shown to be due to the transfer of PSa^– from pseudo-phase of the CNs to the bulk aqueous phase through X^–/PSa^– ion exchange at the surface of the CNs.

Two routes of catalytic hydrochlorination of acetylene were found by the isotopic label method for systems with supported palladium K₂PdCl₄/C and Н₂PdCl₄/C catalysts: with formation of the products of syn- and anti-addition of the H(D)Cl molecule to the triple bond of acetylene. Two isotopic effects that differ in magnitude were determined for these systems from the reaction kinetics and the ratio of the yields of the nondeuterated and monodeuterated isotopomers of the product, which are due to the participation of the H(D)Cl molecule in the two reaction stages: limiting chloropalladation and rapid protodemetallation. The effective activation energies and kinetic isotope effects coincided within the experimental errors, which suggests that the reaction mechanisms are similar and the active centers of the catalysts in systems with K₂PdCl₄/C and Н₂PdCl₄/C are of the same nature.

A theoretically justified mechanism of transmetalation of 2-alkyl substituted titanacyclopropanes with BCl₃ is proposed based on the DFT calculations of the thermodynamic and activation parameters of possible reaction pathways. Based on the data obtained, phenyl- and alkyldichloroboranes were proposed to be used as transmetalating agents along with BCl₃ in the catalytic cycloboration in the presence of Cp₂TiCl₂ and Mg metal. It was shown that the barely accessible 1-phenyl-2-hexylborirane can be synthesized using PhBCl₂.

The structure, texture, and acid properties of platinum catalysts on oxide (Al₂O₃, ZrO₂, ZrO₂–Al₂O₃) and borate-containing supports (B₂O₃–Al₂O₃, B₂O₃–ZrO₂) are studied. The catalysts are tested in the process of hydrocracking sunflower-seed oil at 380°C, 4.0 MPa, and a weight stock feed rate of 1.0 h^–1. It has been found that aluminum oxide (A) contains the γ-Al₂O₃ phase, zirconium dioxide (Z) includes 85 and 15 rel. % of the monoclinic (M) and tetragonal (T) phases, respectively, while zirconium dioxide with the addition of 2.5 wt % Al₂O₃ (ZA) comprises 14 and 86 rel. % of the M–ZrO₂ and T–ZrO₂ phases, respectively. The B₂O₃–Al₂O₃ (BA) and B₂O₃–ZrO₂ (BZ) systems modified with boron oxide (20 wt %) are X-ray amorphous. A Pt/BA catalyst differs from a Pt/A catalyst, while a Pt/BZ catalyst has a larger specific surface area and acidity than Pt/Z and Pt/ZA catalysts and contains Bronsted acidic centers (BACs) along with Lewis acidic centers (LACs). Only LACs are present on the surface of Pt/A, Pt/Z, and Pt/ZA catalysts. The LAC/BAC ratio in Pt/BA and Pt/BZ catalysts is 0.3 and 1.0, respectively. All the catalysts provide complete oil conversion to give C₅₊ hydrocarbons with a yield of 81.7–87.3 wt %. Pt/A catalyzes mainly decarboxylation and hydrogenation–dehydration reactions, while Pt/Z and Pt/ZA provide decarboxylation. The yield of diesel fraction reaches 71.8–73.9 wt % with an n-alkane content of 94.0–95.9 wt %. One-stage oil hydrocracking with the prevalence of hydrodecarbonylation and hydrogenation–dehydration reactions occurs on Pt/BA and Pt/BZ catalysts for 20 h to give the yield of the diesel fraction of at least 81.4 and 74.4 wt % and the total content of iso-alkanes and cycloalkanes of at least 28.3 and 60.7 wt %, respectively.

The effect of potassium and calcium additives on the catalytic activity of the Ce_0.8Zr_0.2O₂ system in the reaction of CO oxidation was studied. With the use of X-ray diffraction analysis, it was found that the Ce_0.8Zr_0.2O₂ and Ce_0.8Zr_0.2O₂–Ca,K samples contained a mixed oxide of cerium and zirconium; the presence of the independent phases of potassium and calcium compounds in the modified system was not detected. With the use of the low-temperature adsorption–desorption of nitrogen, X-ray photoelectron spectroscopy, and temperature-programmed reduction, it was established that the Ce_0.8Zr_0.2O₂–Ca,K system (in spite of the fact that its specific surface area was lower than that of Ce_0.8Zr_0.2O₂) contained more active oxygen on the surface; peroxide and superoxide complexes formed upon the chemisorption of O₂ can act as active oxygen species. This can be the reason for a higher efficiency of the Ce_0.8Zr_0.2O₂–Ca,K system in comparison with that of the unmodified oxide. The results obtained indicate that the ash impurities of Ca and K can increase the catalytic activity of the biomorphic mixed oxides Ce_0.8Zr_0.2O₂ prepared with the use of sawdust as a template.

The effects of the Pd content (0–1 wt %) and the synthesis method (joint impregnation with Ni + Pd and Pd/Ni or Ni/Pd sequential impregnation) on the physicochemical and catalytic properties of Ni–Pd/CeZrO₂/Al₂O₃ were studied in order to develop an efficient catalyst for the conversion of methane into hydrogen-containing gas. It was shown that variation in the palladium content and a change in the method used for the introduction of an active constituent into the support matrix make it possible to regulate the redox properties of nickel cations but do not affect the size of NiO particles (14.0 ± 0.5 nm) and the phase composition of the catalyst ((γ + δ)-Al₂O₃, CeZrO₂ solid solution, and NiO). It was established that the activity of Ni–Pd catalysts in the reaction of autothermal methane reforming depends on the method of synthesis and increases in the following order: Ni + Pd < Ni/Pd < Pd/Ni. It was found that, as the Pd content of the Ni–Pd/CeZrO₂/Al₂O₃ catalyst was decreased from 1 to 0.05 wt %, the ability for self-activation, high activity, and operational stability of the catalyst under the conditions of autothermal methane reforming remained unaffected: at 850°C, the yield of hydrogen was ~70% at a methane conversion of ~100% during a 24-h reaction.

The samples of MnMW/SiO₂ (M = Na, K, and Rb) were synthesized using various synthesis methods under varied heat treatment conditions and their physicochemical properties and activity in the reaction of the oxidative condensation of methane (OCM) were studied for the development of an effective catalyst for the resource-saving process of natural gas conversion into ethylene. It was found that the preparation method exerts an effect on the textural characteristics of the samples and the reducing properties of the cations of manganese and tungsten. It was determined that the composition of a W-containing phase depends on the alkali metal, and a ratio between the polymorphous modifications of SiO₂ is controlled by the method of synthesis and the conditions of catalyst heat treatment. It was established that the yield of C₂ hydrocarbons in the OCM reaction increased with the use of incipient wetness impregnation instead of the method of mixing with a suspension for catalyst preparation and with an increase in the catalyst heat treatment temperature from 700 to 1000°C. The optimum composition of the catalyst and the condition of its synthesis were found: 2Mn_0.8Na₃W/SiO₂ obtained by the impregnation method and calcined at 1000°C ensured the yield of target products of ~20% with a CH₄ conversion of ~35% at a reaction temperature of 850°C.

The interaction of silver with the surface of CeO₂ in the Ag/CeO₂ catalysts prepared by coprecipitation and impregnation techniques was studied by temperature-programmed reduction, X-ray diffraction, and high-resolution transmission electron microscopy. It was shown that coprecipitation technique led to formation of strong silver–support interaction and the epitaxy of silver particles (d₁₁₁ = 2.35 Å) on the surface of CeO₂ (d₁₁₁ = 3.1 Å). This provided incresed catalytic activity in the oxidative dehydrogenation of ethanol at relatively low temperatures (a 15% conversion of ethanol with 100% selectivity for the formation of acetaldehyde was reached at 85°C). Above 130°C, the deep oxidation of ethanol to CO₂ becomes the predominant direction of a catalytic reaction, and the Ag/CеО₂ catalyst obtained by impregnation technique was most active in this region as a consequence of the weaker metal–support interaction.

Composites with the sulfated perfluoropolymer (SFP) (Nafion, etc.)—mesoporous support composition (SFP/support)—are promising solid acid catalysts with strong acid sites and very stable sulfo groups towards leaching processes. The effect of the SFP on the carbon nanofiber (CNF) (SFP/CNF) composite synthesis method, as well as the precursors of the acid phase, on the key acid catalyst characteristics (specific surface area and concentration and accessibility of the acid sites) is studied. The possibility of the direct composite synthesis from SO₂F-polymer latexes obtained as a result of the water emulsion SFP synthesis (without the intermediate stages of isolating the SO₃H form) is shown. The acid phase precursor types which are acceptable for the SFP/CNF composite synthesis (the equivalent polymer weight > 580 g/mol) are selected. The effect of the amount of the supported polymer on the total specific surface area and concentration and accessibility of the composite acid site is investigated. The structure of the synthesized composites is studied (by TEM, SAXS, and isopropanol TPD), and their catalytic activity in the test acetic acid esterification reaction is compared to the catalytic activity of pure polymer samples and acetic acid. It is found that the synthesized SFP/CNF samples outperform commercial SFP/SiO₂ samples (SAC, DuPont), as well as the SFP/CNF samples prepared using polymer solutions in the SO₃H form, in terms of the catalytic characteristics.