M. D. Smolikov

Effect of Thermal Activation of Supported Catalysts Pt/MeOx, Where MOx = Al2O3, CeO2, La2O3, and ZrO2, for Complete Oxidation

A sharp increase in the atomic catalytic activity (ACA) of supported platinum catalysts in the model reaction of n-pentane complete oxidation is found on going from the preliminary calcination temperature of 500–600°C to a temperature of 700°C. ACA increases by an order of magnitude for the Pt/γ-Al2O3 system, ∼3 times for Pt/ZrO2, and ∼1.5 times for Pt/CeO2. The per-gram activities of all catalysts decrease because of a decrease in the dispersion of supported platinum with an increase in the temperature of preliminary calcination.

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.

Isomerization of n-heptane on Pt/MOR/Al2O3 catalysts

Pt/MOR/Al2O3 catalysts with mordenite zeolite contents of 10 to 50 wt % are prepared. Solutions of H2PtCl6 and [Pt(NH3)4]Cl2 are used as precursors of Pt. It is shown by means of transmission electron microscopy (TEM) that the localization of platinum on a MOR/Al2O3 mixed support depends directly on the nature of the metal’s precursor. The catalysts are tested in the isomerization of n-heptane. It is shown that the best samples of catalysts provide yields of the target products (dimethyl and trimethyl substituted isomers of heptanes) on the level of 21 wt % at a temperature of 280°C, while those of a C5+ stable catalyzate are on the level of 79–82 wt %. The catalysts can be used to improve the environmental friendliness of gasolines by employing them in the isomerization of the 70–105°C fraction of directly distilled gasoline.

Study of n-hexane isomerization on Pt/SO4/ZrO2/Al2O3 catalysts: Effect of the state of platinum on catalytic and adsorption properties

The state of surface Pt atoms in the Pt/SO4/ZrO2/Al2O3 catalyst and the effect of the state of platinum on its adsorption and catalytic properties in the reaction of n-hexane isomerization were studied. The Pt-X/Al2O3 alumina-platinum catalysts modified with various halogens (X = Br, Cl, and F) and their mechanical mixtures with the SO4/ZrO2/Al2O3 superacid catalyst were used in this study. With the use of IR spectroscopy (COads), oxygen chemisorption, and oxygen-hydrogen titration, it was found that ionic platinum species were present on the reduced form of the catalysts. These species can adsorb to three hydrogen atoms per each surface platinum atom. The specific properties of ionic platinum manifested themselves in the formation of a hydride form of adsorbed hydrogen. It is believed that the catalytic activity and operational stability of the superacid system based on sulfated zirconium dioxide were due to the participation of ionic and metallic platinum in the activation of hydrogen for the reaction of n-hexane isomerization.

Preparing and studying Pt/WO3/ZrO2 catalysts for the isomerization of n-heptane

The effect of the temperature of WO3/ZrO2 support calcination in the range of 700–1000°C on the phase composition, acid, and catalytic properties of Pt/WO3/ZrO2 catalysts is studied. Using ammonia TPD, it is found that calcination in the temperature range of 850–950°C results in the formation of strong acid sites that increase the yield of the target products of the reaction of n-heptane isomerization: high octane di- and trimethylsubstituted isomers. DRIFT is used to determine the role of catalyst calcination in an air flow plays in the formation of charged platinum atoms, which results in higher catalyst activity.

Studying the role of the state of platinum in Pt/SO4/ZrO2/Al2O3 catalysts in the isomerization of n-hexane

Samples of SO4/ZrO2/Al2O3 and Pt/Al2O3 Pt/Al2O3 catalysts and their physical mixtures are prepared, and the catalytic properties of the samples in n-hexane isomerization are studied. The considerable effect of the state of platinum on the catalytic performance of the samples is revealed. IR spectroscopy (COads), oxygen chemisorption, and oxygen-hydrogen titration show that the reduced catalysts contain ionic forms of platinum capable of adsorbing up to three hydrogen atoms per each surface atom of platinum. By means of H/D isotopic exchange, it is found that specific properties of ionic platinum are apparent in the formation of the hydride form of adsorbed hydrogen. It is speculated that the activity and stability of catalysts based on sulfated zirconia in n-hexane isomerization can be attributed to the involvement of ionic and metallic platinum in the activation of hydrogen. The results can be used to develop effective catalysts for the isomerization of C5–C6 gasoline fractions in order to obtain the isomerizate as a high-octane additive for modern gasolines.

Pt/BEA–Al2O3 catalysts for the isomerization of benzene/heptane mixtures. I: Optimizing the support’s composition

Pt/BEA–Al2O3 catalysts for the hydroisomerization of benzene-containing gasoline fractions are studied using a model feedstock (20% benzene and 80% n-heptane). The catalysts are prepared by varying the zeolite content from 5 to 70 wt % at a constant Pt loading of 0.3 wt % in all samples, with an aqueous H2PtCl6 solution being used as the Pt precursor. The acid properties of the samples are studied by means of temperature-programmed desorption (TPD). The effect of the support’s zeolite/binder ratio on the activity of the catalysts is determined: an increase in the zeolite content raises the system’s acidity and shifts the range of the reaction toward lower temperatures. The optimum zeolite/binder ratio is found to be 30% BEA/70% Al2O3. Changing the SiO2/Al2O3 ratio of the zeolite from 25 to 40 is shown to have no noticeable effect on catalyst activity. The use of the catalysts supported on 30% BEA/70% Al2O3 in the hydroisomerization of benzenecontaining gasoline fractions can be recommended for improving environmental performance.

Synthesis and study of Pt(Pd)-containing WO3/ZrO2 catalysts for isomerization of n-heptane

The effect of zirconia precursor in Pt-containing WO3/ZrO2 catalysts on isomerization of n-heptane was studied. Samples synthesized with zirconium sulfate as a ZrO2 precursor were shown to be more ...

A study of the effects produced by tin modification of alumina-supported Pt/SO4/ZrO2 catalysts for n-hexane isomerization

The modifying effect of tin introduced at different steps from various tin precursors on characteristics of n-hexane isomerization in the presence of supported Pt/SZ/Al2O3(Sn) catalysts was studied. The addition of Sn was shown to substantially affect the porosity characteristics of the catalysts and dispersion (particle size) of the active phase of tetragonal zirconia. The use of Sn(IV) hydroxide as an additive to the initial aluminum hydroxide allowed obtaining the supported catalyst with the particle size of the t-ZrO2 active component 3.2 nm and specific surface area of zirconia 294 m2/g. At a zirconia content of ca. 20 wt.% the catalytic performance of the catalyst in n-hexane isomerization approached the performance of the bulk samples in which ZrO2 content attained 70-75 wt.%.

Isomerization of n-heptane over Pt(Pd)/WO3/ZrO2 catalysts

The effect of Pt and Pd concentration in WO3/ZrO2 catalysts on their acidic and catalytic properties in isomerization of n-heptane has been studied. It was found that the highest yield of the target products of the reaction – di- and trimethyl substituted (DTMS) high-octane heptane isomers – is reached on the samples with the platinum content of 1.0–1.5 wt.% and is equal to 29.2–29.3 wt.%. When Pd is used as a metallic component, the DTMS yield of ca. 29.1 wt.% is attained at a palladium content of 0.1 wt.%. Pt(Pd)/WO3/ZrO2 catalysts were subjected to thermal treatment in a hydrogen medium and effect of the treatment conditions on isomerization of n-heptane was investigated. The reduction of the catalysts at temperatures above 300°C was shown to reduce tungsten atoms with the formation of Lewis acid sites (LAS), thus promoting the side reactions leading to cracking of heptanes.The effect of Pt and Pd concentration in WO3/ZrO2 catalysts on their acidic and catalytic properties in isomerization of n-heptane has been studied. It was found that the highest yield of the target products of the reaction – di- and trimethyl substituted (DTMS) high-octane heptane isomers – is reached on the samples with the platinum content of 1.0–1.5 wt.% and is equal to 29.2–29.3 wt.%. When Pd is used as a metallic component, the DTMS yield of ca. 29.1 wt.% is attained at a palladium content of 0.1 wt.%. Pt(Pd)/WO3/ZrO2 catalysts were subjected to thermal treatment in a hydrogen medium and effect of the treatment conditions on isomerization of n-heptane was investigated. The reduction of the catalysts at temperatures above 300°C was shown to reduce tungsten atoms with the formation of Lewis acid sites (LAS), thus promoting the side reactions leading to cracking of heptanes.