O. B. Belskaya

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.

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.

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.

Hydroisomerization of benzene-containing gasoline fractions on a Pt/SO42−-ZrO2-Al2O3 catalyst: II. Effect of chemical composition on acidic and hydrogenating and the occurrence of model isomerization reactions

The acidic and hydrogenating of Pt/SO42−-ZrO2-Al2O3 samples containing from 18.8 to 67.8 wt % Al2O3 as a support constituent were studied by the IR spectroscopy of adsorbed CO and pyridine, and the model reactions of n-heptane and cyclohexane isomerization on these catalysts were examined. The total catalyst activity in the conversion of n-heptane decreased with the concentration of Al2O3; this manifested itself in an increase in the temperature of 50% n-heptane conversion from 112 to 266°C and in an increase in the selectivity of isomerization to 94.2%. In this case, the maximum yield of isoheptanes was 47.1 wt %, which was reached on a sample whose support contained 67.8 wt % Al2O3. A maximum yield (69.6 wt %) and selectivity (93.7%) for methylcyclopentane formation from cyclohexane were also reached on the above catalyst sample. This can be explained by lower concentrations of Lewis and Brønsted acid sites in the Pt/SO42−-ZrO2-Al2O3 system, as compared with those in Pt/SO42−-ZrO2. The experimental results allowed us to make a preliminary conclusion that the Pt/SO42−-ZrO2-Al2O3 catalyst whose support contains 67.8 wt % Al2O3 is promising for use in the selective hydroisomerization of benzene-containing gasoline fractions in the thermodynamically favorable process temperature range of 250–300°C.

FTIR Spectroscopy of Adsorbed Probe Molecules for Analyzing the Surface Properties of Supported Pt (Pd) Catalysts

Supported metal catalysts are important for many fields of applied chemistry, including chemical synthesis, petrochemistry, environmental technology, and energy generation/storage. For prediction of catalyst performance in a chosen reaction and optimization of its functions, it is necessary to know the composition of the surface active sites and have methods for estimating their amount and strength. One of the most available and well-developed methods for studying the composition and structure of the surface functional groups of supported metal catalysts is vibrational spectroscopy, in particular with the use of adsorbed probe molecules.

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+.

Effect of carbon support nature and palladium content on the properties of Pd/C catalysts in hydrogenation of benzaldehyde

In the series of studied Pd/C catalysts, the highest selectivity for benzyl alcohol formation with complete conversion of benzaldehyde was demonstrated by the sample containing 1% palladium supported on carbon nanotubes when the reaction was carried out at 40 °C and 0.5 MPa. The 0.3% Pd/C catalysts have low activity. Increasing the palladium content and raising the reaction temperature leads to an increase in the toluene fraction in the reaction products.

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.

Use of Platinum Carbonyl Complexes in the Synthesis of Pt/MgAlO x Catalysts

Pt/MgAlOx samples have been obtained by the adsorption of platinum carbonyl complexes on aluminum-magnesium oxides with Mg: Al = 2, 3, and 4. The composition of the adsorbed complexes has been determined. The catalysts synthesized from the carbonyl precursor show a higher activity in propane dehydrogenation and are less prone to deactivation than the catalysts prepared using platinum chloro complexes.

Catalysts on the basis of anion-modified metal oxides for production of ecologically pure components of motor fuels

Experimental evidence on the production, structure, and physiochemical properties of aluminum, zirconium, and titanium oxides modified with halides, sulfates, and boron and tungsten oxides. Information on the application of anion-modified metal oxides as catalysts in the production of ecologically pure components of motor fuels, with decreased contents of aromatic hydrocarbons and sulfur compounds. Therewith, along with traditional hydrocarbon oligomerization, isomerization, alkylation reactions, actual arene hydroisomerization processes and production of diesel fuels from vegetable materials are considered.