M. A. Kerzhentsev

Development and Testing of Granular Catalysts for Combustors of Regenerative Gas Turbine Plants

Two types of granular catalysts for effective methane combustion in combustors of gas turbine plants (GTPs) were developed: (1) catalysts based on noble metals with a low Pd content (1–2 wt %), characterized by a low methane ignition temperature, and (2) catalysts based on manganese oxides and hexaaluminates, which have an increased thermal stability. The methane oxidation kinetics was investigated, and combustion in the catalyst chamber of the GTP was simulated. For optimizing the combustion technology, the following two-step process using a combined catalytic package is suggested. The inlet zone of the combustor is filled with a highly active Pd catalyst, which initiates methane oxidation and ensures that the temperature at the exit of this zone is the initial temperature of methane combustion. This takes place in the next zone, which is filled with an oxide catalyst tolerant to high temperatures. The pilot testing of the catalysts was carried out in a model catalytic combustor. The results are in satisfactory agreement with calculated data. Long-term tests indicate the high stability of the catalysts. The Pd catalyst was demonstrated to retain its high activity and to provide an ignition temperature of 240°C. The initial activity of the hexaaluminate-based catalysts remains unchanged after tests at 930°C. The use of a combined charge of the palladium (7–15%) and manganese (85–93%) catalysts in the model GTP combustor allows a high natural gas combustion efficiency to be achieved at a low level of hazardous emissions (NOx, 0–1 ppm; CO, 1–3 ppm; hydrocarbons, 3–10 ppm).

Characterization of new catalysts based on uranium oxides

Catalysts based on uranium oxides were systematically studied for the first time. Catalysts containing various amounts of uranium oxides (5 and 15%) supported on alumina and mixed Ni-U/Al2O3 catalysts were synthesized. The uranium oxide catalysts were characterized using the thermal desorption of argon, the low-temperature adsorption of nitrogen, X-ray diffraction analysis, and temperature-programmed reduction with hydrogen and CO. The effects of composition, preparation conditions, and thermal treatment on physicochemical properties and catalytic activity in the reactions of methane and butane oxidation, the steam and carbon dioxide reforming of methane, and the partial oxidation of methane were studied. It was found that a catalyst containing 5% U on alumina calcined at 1000°C was most active in the reaction of high-temperature methane oxidation. For the Ni-U/Al2O3 catalysts containing various uranium amounts (from 0 to 30%), the introduction of uranium as a catalyst constituent considerably increased the catalytic activity in methane steam reforming and partial oxidation.

Effect of support modification on the physicochemical properties of a NiPd/Al2O3 catalyst for the autothermal reforming of methane

For the development of effective catalysts for the autothermal reforming of methane, the NiPd catalysts were synthesized based on modified aluminum oxide and their physicochemical properties were studied using X-ray diffraction analysis, low-temperature nitrogen adsorption, transmission electron microscopy, and temperature-programmed reduction with hydrogen. It was found that the variation of modifying components (CeO2, ZrO2, La2O3, Ce0.5Zr0.5O2, and La2O3/Ce0.5Zr0.5O2) and their concentrations (10–30 wt %) makes it possible to regulate the particle size of NiO, the composition of a Ni-containing phase (NiO, La2NiO4, NiAl2O4, or Ni-La-Al-O) and the redox properties of nickel ions. It was shown that the average particle size of NiO increased from 6.7 to 17.5 nm in the following order of supports: La2O3/Al2O3 < La2O3/Ce0.5Zr0.5O2/Al2O3 < Al2O3 < Ce0.5Zr0.5O2/Al2O3 < CeO2/Al2O3 < ZrO2/Al2O3. On the introduction of the modifying oxides CeO2 and ZrO2 into aluminum oxide, the fraction of nickel in the composition of NiAl2O4 decreased and, therefore, the fraction of difficult-to-reduce Ni2+ decreased. The addition of La2O3 and La2O3/Ce0.5Zr0.5O2 strengthened the interaction of nickel cations with the support up to the formation of Ni-La-Al-O and La2NiO4 phases and increased the fraction of difficult-to-reduce Ni2+ ions. The resulting NiPd catalysts are promising in the catalysis of the autothermal reforming of methane.

Effect of the nature of sulfur compounds on their reactivity in the oxidative desulfurization of hydrocarbon fuels with oxygen over a modified CuZnAlO catalyst

The reactivity of thiophene, dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT), which are the representatives of the main classes of sulfur compounds that are the constituents of diesel fractions, was studied in the course of their oxidative desulfurization with oxygen on a CuO/ZnO/Al2O3 catalyst modified with boron and molybdenum additives. At T ≥ 375°C, the reactivity increased in the order thiophene < DBT < 4,6-DMDBT. The degree of sulfur removal in the form of SO2 from hydrocarbon fuel, which was simulated by a solution of 4,6-DMDBT in toluene, was 80%. Under the assumption of a first order reaction with respect to sulfur compound and oxygen, the apparent activation energies of the test processes were calculated. An attempt was made to reveal the role of the adsorption of sulfur compounds in the overall process of oxidative desulfurization with the use of X-ray diffraction analysis, X-ray photoelectron spectroscopy, and differential thermal and thermogravimetric analysis with the massspectrometric monitoring of gas phase composition.

Structural and morphological properties of Ce 1– x M x O y (M = Gd, La, Mg) supports for the catalysts of autothermal ethanol conversion

A complex of physicochemical methods (powder XRD analysis, transmission and scanning electron microscopy, electron spectroscopy of diffuse reflectance, low-temperature nitrogen adsorption) is used for the comparative study of structural and morphological properties of oxide supports Ce1–xMxOy (M = Gd, La, Mg; x = 0-0.5; 1.5 ≤ y ≤ 2.0) for catalysts for the autothermal reforming of bioethanol to a hydrogen-bearing gas. It is shown that Ce1–xMxOy samples synthesized by the method of ester polymer precursors are mesoporous materials being the homogenous substitutional solid solutions with the fluorite-type cubic structure. The structural and textural properties of the Ce1–xMxOy materials are regulated by varying the type of the dopant cation (M = Gd, La, Mg), the molar ratio M/Ce (0, 0.1, 0.25, 1), and heat treatment conditions (temperature 300-800 °C; duration 4-24 h). The relationship between the synthesis parameters and the characteristics of the Ce1–xMxOy materials is found.

Capillary microreactor with a catalytic coating based on mesoporous titanium dioxide for the selective hydrogenation of 2-methyl-3-butyn-2-ol

A continuously working capillary microreactor with a catalytic coating based on mesoporous titanium dioxide with embedded Pd nanoparticles was tested in a reaction of the selective hydrogenation of 2-methyl-3-butyn-2-ol (MBI). The catalytic coatings were obtained by the supporting of a carrier sol, which contained colloidal Pd nanoparticles, onto the internal wall of a quartz capillary with a diameter of 250 μm in the dynamic mode. The effects of the concentration of MBI in methanol (0.05–0.2 mol/L), the partial pressure of hydrogen (0.28–1.0 atm), and the reaction temperature (308–333 K) on the catalyst activity and the selectivity of reaction were studied. High selectivity for the formation of the semi-hydrogenated product 2-methyl-3-buten-2-ol was reached at 313 K in an atmosphere of pure hydrogen. At a conversion of 99.9%, the selectivity was 92.3%, which is 15.5% higher than that in a batch reactor. The rate of hydrogenation on the Pd/TiO2 coating was higher by one order of magnitude than that on a commercial Lindlar catalyst. The coating remained stable upon the continuous passage of the flow of a reaction mixture for 500 h.

Cu-Zn-Al-O catalysts for the oxidative desulfurization of dibenzothiophene, a typical sulfur-containing compound of the diesel fraction

The possibility of oxidative desulfurization of dibenzothiophene dissolved in toluene as a model organosulfur compound of diesel fuel in the presence of catalytic CuZnAl compositions was studied. It was shown that the CuZnAl catalysts at 350–450°C ensure sulfur removal from the model fuel to the extent of up to 40–45%. Part of the sulfur is removed as SO2, and some sulfur is absorbed on the catalyst surface.

Oxidative condensation of methane in the presence of modified MnNaW/SiO2 catalysts

The effects of cationic (Ce, Zr, and La) and anionic (S, P, and Cl) admixtures on the activity and physicochemical properties of MnNaW/SiO2 were studied in order to optimize the composition of a catalyst for the oxidative condensation of methane (OCM). It was found that OCM process characteristics can be regulated by varying the type (Ce, Zr, La, S, P, and Cl) and concentration (0.5–5 wt %) of a modifying admixture. For the modified MnNaW/SiO2 catalysts, the yield of the target reaction products increased in the following order of modifying admixtures: S < Zr < P < Ce < La < Cl. The addition of lanthanum, cerium, or phosphorus admixtures insignificantly affected the activity of the MnNaW/SiO2 catalyst, whereas the introduction of sulfur or zirconium led to a decrease in the yield of C2 hydrocarbons. Modification with chlorine improved process characteristics and shifted a maximum yield of C2 hydrocarbons to the low-temperature region. It was established that the introduction of lanthanum considerably improved the stability of catalyst operation. The catalyst composition 2Mn-1.6Na-3.1W-2La/SiO2 was developed to afford a 22% yield of target C2 hydrocarbons at a 54% conversion of methane after a 24-h reaction performed under optimum conditions (reaction temperature, 800°C; reaction mixture flow rate, 117 mL min−1gCat−1 and O2/CH4 molar ratio, 0.5).

Effect of the support composition on the physicochemical properties of Ni/Ce 1– x La x O y catalysts and their activity in an autothermal methane reforming reaction

The effect of the Ce1–xLaxOy (x = 0–1, 1.5 ≤ y ≤ 2.0) support composition on the physicochemical properties of supported Ni catalysts and their activity in autothermal methane reforming was studied. The textural and structural characteristics of Ce1–xLaxOy and Ni/Ce1–xLaxOy samples and the process of their reduction in an atmosphere of hydrogen were examined using a set of techniques (low-temperature nitrogen adsorption, X-ray diffraction analysis, transmission electron microscopy, and thermal analysis). It was established that the Ce1–xLaxOy supports (x = 0–0.9) are mesoporous materials containing a fluorite-like solid solution based on cerium dioxide, in which the unit cell parameter increases and the average crystallite size decreases with the mole fraction of La. It was shown that the average size and composition of Ni-containing particles in the Ni/Ce1–xLaxOy catalysts depends on the composition of the support: at x = 0–0.8, a phase of NiO was formed, whereas a phase of LaNiO3 was formed at x = 0.9–1. The dispersity of the active constituent and its stability to agglomeration increased as the mole fraction of La in the Ce1–xLaxOy support was increased from 0 to 0.8, whereas the reduction of Ni-containing oxide particles shifted to the higher temperature region. The Ni/Ce1–xLaxOy catalysts provided high methane conversion (96–100%) and the yield of H2 (35–55%). The yield of hydrogen increased with decreasing the mole fraction of La in the Ce1–xLaxOy support composition; this can be caused by a decrease in the fraction of difficult-to-reduce Nin+ cations due to the weakening of metal–support interactions.

Synthesis of nanosized thin-film bimetallic catalysts based on mesoporous TiO2 for microstructured reactors

A synthetic procedure for the production of effective catalysts for the selective hydrogenation of organic substrates was developed, and the samples of thin-film Pt-Sn/TiO2 materials, which are characterized by high dispersity and a narrow size distribution of bimetallic particles in a mesoporous matrix of titanium dioxide, were prepared. With the use of a set of physicochemical techniques (low-temperature nitrogen adsorption, X-ray diffraction analysis, thermal analysis, and transmission electron microscopy), the formation and surface properties of the mesoporous Pt-Sn/TiO2 materials as powder and coatings on the surfaces of silica capillaries and plates were studied. Based on the effects of the sol composition and calcination temperature on the texture properties of TiO2, an optimum sol composition (1Ti(O-iPr)4: 0.009 F127: 0.13 HNO3: 1.3 H2O: 25 C2H5OH) and heat treatment conditions (calcination at 673 K; stepwise increase in the temperature) were determined to form a mesoporous coating with a specific surface area of 130 m2/g and an average pore diameter of 5.4 nm. It was found that the concentrations of metals (0.5–4 wt %), average particle sizes (1.0–3.5 nm), and particle size distributions in the Pt-Sn/TiO2 materials can be mainly regulated by varying the nature of the solvent, the concentration of Pt-Sn carbonyl complexes, and the time of adsorption, whereas the electronic state of metals can be fine-tuned by thermal treatment conditions. In an oxidizing atmosphere, the Pt-Sn carbonyl complexes decomposed with the formation of a two-phase system (Pt○ and SnO2). Thermal treatment in a vacuum and an inert or reducing atmosphere led to the formation of bimetallic phases (PtSn and Pt3Sn), whose stucture was regulated by the composition of a gas atmosphere and by the calcination temperature.