T. I. Gulyaeva

Formation of platinum sites on layered double hydroxides type basic supports: I. Effect of the nature of the interlayer anion on the structure characteristics of the layered aluminum-magnesium hydroxide and the formation of an oxide phase

A layered aluminum-magnesium hydroxide of the hydrotalcite type containing interlayer carbonate counterions (HT-CO3) and activated hydrotalcite containing interlayer OH− ions (HT-OH) were studied for the subsequent use as the precursors of supports for platinum catalysts. It was found that the nature of an interlayer anion in the composition of an aluminum-magnesium layered hydroxide is an important factor affecting both the formation of the oxide support and its texture characteristics. The replacement of the interlayer CO32− anion by OH− resulted in changes in the structural parameters of the initial double hydroxide: a decrease in the interlayer distance with the retention of the Mg/Al ratio and an increase in the imperfection of the layered material. X-ray diffraction studies in the temperature range of 30–900°C showed that HT-OH is characterized by the ability to form low-temperature spinel at 375°C. As a result, two types of aluminum-magnesium oxide supports, which were characterized by different pore space organizations at the same Mg: Al ratio, were obtained from the given layered hydroxides.

Chemical composition optimization and characterization of the NiO/B2O3-Al2O3 system as a catalyst for ethylene oligomerization

The samples of the NiO/B2O3-Al2O3 system with NiO contents from 0.48 to 38.30 wt % were synthesized by the impregnation of borate-containing alumina (20 wt % B2O3). It was found that nickel oxide occurred in an X-ray amorphous state in the samples containing to 23.20 wt % NiO. At a NiO content of 4.86 wt % or higher, the support was blocked by the modifier to cause a decrease in the specific surface area from 234 to 176 m2/g and in the amount of acid sites from 409–424 to 333 μmol/g. An extremal character of the dependence of catalyst activity in ethylene oligomerization on NiO content was found with a maximum in the range of 4.86–9.31 wt %. Based on spectroscopic data, it was found that ethylene activation on the NiO/B2O3-Al2O3 catalyst can be associated with the presence of Ni2+ cations, which chemically interact with the support. The catalyst containing 4.86 wt % NiO at 200°C, a pressure of 4 MPa, and an ethylene supply rate of 1.1 h−1 provided almost complete ethylene conversion at the yield of liquid oligomerization products to 90.0 wt %; the total concentration of C8+ alkenes in these products was 89.0 wt %.

Formation of platinum sites on layered double hydroxide type basic supports: II. Effect of the nature of the interlayer anion of the layered aluminum-magnesium hydroxides on platinum binding and Pt/MgAlO x formation

The interaction of aqueous H2PtCl6 solutions with hydrotalcite-type aluminum-magnesium hydroxides differing in the nature of their interlayer anion is reported. In the case of CO32− as the interlayer anion, the introduction of the platinum(IV) chloro complex does exerts no significant effect on the structural properties of the support, on its thermal decomposition dynamics, and on the textural characteristics of the resulting oxide phase. The binding of the platinum complexes to “activated hydrotalcite” with interlayer OH− anions increases the interplanar spacing and enhances the thermal stability of the layered structure. This is accompanied by marked changes in textural characteristics of the material, leading to the formation of a nearly monodisperse mixed oxide phase. In the Pt/MgAlOx samples obtained by reductive treatment, a considerable proportion of platinum is in the form of planar particles, and this corroborates the hypothesis that the metal complex at the sorption stage is mainly localized in the interlayer space of this support. Platinum binds to the support as chloro complexes via rapid anion exchange, and these bound platinum species are characterized by a higher reduction temperature.

Benzene hydroisomerization over Pt/MOR/Al2O3 catalysts

Benzene hydroisomerization is among the promising processes converting benzene into methylcyclopentane (MCP), which is an environmentally friendlier, octane boosting component of motor fuels. Benzene hydroisomerization into MCP over the Pt/MOR/Al2O3 (MOR = mordenite) catalytic system is reported here. The dependence of the yield of the target product on the acidic properties of the support and platinum precursor ([Pt(NH3)4]Cl2 or H2PtCl6) have been investigated in order to optimize the catalyst composition. The acidic properties of the surface have been altered by introducing 30–95 wt % alumina into the support. Catalytic activity has been measured in the hydroisomerization of cyclohexane and a benzene (20 wt %) + n-heptane (80 wt %) mixture in a flow reactor at 250–350°C, 1.5 MPa, H2: CH = 3: 1, a cyclohexane LHSV of 6 h−1, a mixed feedstock LHSV of 2 h−1, a catalyst bed volume of 2 cm3, and catalyst pellet sizes of 0.25–0.75 mm. The most efficient catalyst for cyclohexane and n-heptane isomerization and benzene hydroisomerization is the platinum-containing catalyst (0.3 wt % Pt) whose support consists of 30 wt % MOR and 70 wt % Al2O3. The highest yield of the target products of isomerization in the presence of this catalyst is attained in the temperature range from 280 to 310°C, which is thermodynamically favorable for MCP formation from benzene. This indicates that this catalyst is promising for the hydroisomerization of benzene-containing gasoline fractions. Use of H2PtCl6, a readily available chemical, as the platinum precursor is favorable for commercialization of the catalyst and ensures price attractiveness in its industrial-scale manufacturing.

Influence of a doubly charged cation nature on the formation and properties of mixed oxides MAlOx (M = Mg2+, Zn2+, Ni2+) obtained from the layered hydroxide precursors

Influence of the nature of a doubly charged cation in the layered double hydroxides (LDH) on the conditions of formation and properties of mixed oxide phase MAlOx (M = Mg2+, Zn2+ and Ni2+), its ability to reconstruct the structure of the original precursor under contact with water has been studied. Hydrotalcite-like compounds and corresponding oxides with different M2+: M3+ ratio were investigated by XRD, TEM, TG-DTG-DTA, 27Al NMR, N2 adsorption, and differentiating dissolution. It has been found that the nature of the cation M2+ influences the conditions of LDH thermal decomposition, structural and textural characteristics of the formed mixed oxides. The obtained data can be used to synthesize the oxide supports with desired acid-base and adsorption properties.

Formation of platinum sites on layered double hydroxide type basic supports: III. Effect of the mechanism of [PtCl6]2− complex binding to aluminum-magnesium layered double hydroxides on the properties of supported platinum in Pt/MgAlOx catalysts

While synthesizing platinum catalysts supported on aluminum-magnesium oxides (Pt/MgAlOx), we established that, in the binding of the Pt(IV) chloro complex to aluminum-magnesium layered double hydroxides (LDHs), the mechanism of the metal complex-support interaction depends on the nature of the interlayer anion of the LDH. The synthesis may yield chemically identical Pt/MgAlOx samples differing in the particle size and electronic structure of supported platinum. The higher dehydrogenating activity of the catalyst obtained by binding the [PtCl6]2− complex in the interlayer space of LDH via exchange with interlayer OH− anions is possibly due to the larger proportion of metallic platinum (Pt0) in this catalyst. In the catalyst prepared from hydrolyzed platinum complex species using LDH with CO32− interlayer anions, platinum is mainly in an oxidized state similar to Pt2+.

(CuO-CeO2)/glass cloth catalysts for selective CO oxidation in the presence of H2: The effect of the nature of the fuel component used in their surface self-propagating high-temperature synthesis on their properties

The potential of surface self-propagating high-temperature synthesis (SSHS) for obtaining (CuO-CeO2)/glass cloth catalysts is demonstrated. The dependence of the structural and catalytic properties of the catalysts on their preparation conditions (nature of the fuel component) is considered. X-ray diffraction, electron microscopy, and EXAFS data suggest that the short-term action of high temperature in the SSHS leads to the complete decomposition of the precursors and has an effect on the distribution of the resulting phases. According to H2 TPR and XPS data, the degree of dispersion of CuO and the electronic state of the reacting CuO and CeO2 phases depend on the choice of fuel. This is likely due to fuels varying in the amount of heat released in their combustion. The degree of dispersion of CuO and the total contribution from Cu1+ and Ce4+ to the electronic state of the active component increase as the standard enthalpy of combustion increases in the urea < glycerol < citric acid order. This leads to an increase in the catalytic activity of the (CuO-CeO2)/glass cloth system in selective CO oxidation.

Selective oxidation of carbon monoxide in hydrogen-containing gas on CuO-CeO2/Al2O3 catalysts prepared by surface self-propagating thermal synthesis

The CuO-CeO2/Al2O3 catalysts for the selective oxidation of CO in hydrogen-containing mixtures were prepared by surface self-propagating thermal synthesis (SSTS) with the use of cerium nitrate Ce(NO3)3, the ammonia complex of copper acetate [Cu(NH3)4](CH3COO)2, and citric acid C6H8O7 as a fuel additive. The effect of the C6H8O7/Ce(NO3)3 molar ratio on the catalyst activity and selectivity for oxygen was studied. The catalyst samples were studied by X-ray diffraction (XRD) analysis, temperature-programmed reduction (TPR-H2), IR spectroscopy of adsorbed CO, and transmission electron microscopy (TEM). It was found that an increase in the C6H8O7/Ce(NO3)3 ratio resulted in an increase in the degree of dispersion of the resulting CeO2 phase. The greatest amount of dispersed CuO particles, which are responsible for catalytic activity in the oxidation of CO, was formed at C6H8O7/Ce(NO3)3 = 1.

Study of Pt/MgAlO x catalysts in n -decane dehydrogenation

The properties of Pt/MgAlOx catalysts based on aluminum–magnesium layered hydroxides have been investigated in n-decane dehydrogenation. The n-decene formation selectivity depends on the Mg/Al ratio in the support, on the platinum complex binding conditions, and on the platinum content of the catalyst. Increasing the proportion of magnesium decreases the number of acid cites in the support and changes the properties of supported platinum. As a result, the n-decene formation selectivity under the appropriate conditions reaches 90% without a modifier added.

Effect of chemical composition and method of preparation on the physicochemical properties of the NiO/B2O3-Al2O3 system and its catalytic activity in ethylene oligomerization

The effect the chemical composition of a support, the content of nickel, and the method of its binding has on the physicochemical and catalytic properties of the NiO/B2O3-Al2O3 system is studied. The boron oxide content in the support is varied from 2 to 30 wt %, while the nickel concentration is 0.59–3.18 wt %. The catalyst samples are studied via X-ray diffraction analysis, temperature-programmed desorption of ammonia, IR spectroscopy (including that of adsorbed CO), and UV-VIS diffuse reflectance spectroscopy. Tests of the catalysts in ethylene oligomerization are conducted in a fixed-bed flow reactor at a temperature of 200°C, a pressure of 1 MPa, and a space velocity of ethylene of 0.5 h−1. The feedstock is an ethylene-methane gas mixture containing 30 wt % of ethylene. It is suggested that the activity of the NiO/B2O3-Al2O3 system in ethylene oligomerization can be attributed to the formation of octahedral Ni2+ cations environed by borate anions on the surface of the system. The most active catalysts contain 2–3 wt % Ni and 10–20 wt % B2O3 in the supports. The method of preparation (adsorption binding or impregnation) has little effect on the state of nickel in the NiO/B2O3-Al2O3 system samples and their catalytic properties. The prepared catalysts are characterized by the ease of preparation, availability, and a low cost of the initial materials, as compared to known catalysts.