Bimetallic Rh-Co/ZrO<Subscript>2</Subscript> catalysts for ethanol steam reforming into hydrogen-containing gas

The properties of supported bimetallic Rh-Co/ZrO₂ catalysts in ethanol steam reforming into hydrogen-containing gas were studied. The particles of Rh-Co solid solutions on the catalyst surface were prepared by the thermal decomposition of the double complex salt [Co(NH₃)₆][Rh(NO₂)₆] and the solid solution Na₃[RhCo(NO₂)₆]. It was found that the bimetallic Rh-Co/ZrO₂ catalysts exhibited high activity in the reaction of ethanol steam reforming. The equilibrium composition of reaction products was attained at 500–700°C and a reaction mixture space velocity of 10000 h⁻¹.     

Synthesis characterization and catalytic evaluation of Ni/ZrO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> aerogels catalysts

The Ni/ZrO₂/SiO₂ aerogels catalysts were synthesized via three different routes: (i) impregnation ZrO₂–SiO₂ composite aerogels with a aqueous solution of Ni(NO₃)₂, (ii) impregnation SiO₂ aerogels with a mixed aqueous solution of Ni(NO₃)₂ and ZrO(NO₃)₂ · 2H₂O, (iii) one-pot sol–gel procedure from precursors Ni(NO₃)₂/ZrO(NO₃)₂ · 2H₂O/Si(OC₂H₅)₄. These catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), ammonia temperature-programmed desorption (NH₃-TPD), N₂ adsorption–desorption isotherms and Fourier transform infrared (FT-IR). The Liquid-phase hydrogenation of maleic anhydride (MA) was performed over these catalysts. The results revealed that the different preparation routes result in a difference between the obtained samples, concerning the crystal structure and composition, surface acidity, mixed level of each component, texture, and catalytic selectivity.     

Effect of composition changes on properties and defect structure of crystalline Sm-doped ZrO<Subscript>2</Subscript>

Polymorphous structure, electrical conductivity, absorption coefficient, refractive index, and mechanical characteristics of crystalline system ZrO₂ + x Sm₂O₃ (x = 4–43 mol %) is investigated. Vickers microhardness is investigated by the well-known quasi-static indentation method. Plastic microhardness and the effective elastic modulus are studied by the depth-sensing indentation technique. Special attention is devoted to the ordered defect fluorite structure, pyrochlore phase Sm₂Zr₂O₇, observed for x = 43 mol %. Potential applications of the investigated system are discussed. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 4, pp. 402–411. The text was submitted by the authors in English.     

Influence of ZrO<Subscript>2</Subscript> on the physicochemical properties of the ZrO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> binary system

A series of ZrO₂-TiO₂ mixed oxides with different weight ratios (5, 20, and 30% ZrO₂) were prepared by wet impregnation of TiO₂-P25 Degussa with certain amounts of ZrO(NO₃)₂·6H₂O (Fluka) dissolved in deionised water. The samples were characterized by the XRD, , , , and BET methods. An increase in ZrO₂ content shifted the phase transition temperature (anatase into rutile) toward higher temperatures. X-ray diffraction using an Anton Paar XRK900 reactor chamber indicated that, in the case of samples containing ZrO₂, an additional diffraction peak appeared after cooling down to 25°C. This peak could be attributed to a polymorph of TiO₂ such as in the single crystal of anatase or hexagonal form of TiO₂ which appears in the presence of ZrO₂. Generally, the preparation of dioxide systems can modify the properties of pure compounds or generate new catalytic sites as a result of strong interaction between ZrO₂ and TiO₂ oxides. The binary systems exhibit advantages like strong acidity, extended specific surface area, and high thermal stability in comparison with TiO₂. The article is published in the original.     

Ethanol dehydrogenation on copper catalysts with ytterbium stabilized tetragonal ZrO<Subscript>2</Subscript> support

The physicochemical and catalytic properties of Cu-containing crystalline zirconia, obtained via sol–gel synthesis in the presence of Yb³⁺ ions and polyvinylpyrrolidone, are studied. DTG/DSC, TEM, XRD and BET methods are used to analyze the crystallization, texture, phase uniformity, surface and porosity of ZrO₂ nanopowders. It is shown that increasing the copper content (1, 3, and 5 wt % from ZrO₂) raises the dehydrogenation activity in the temperature range of 100–400°C and lowers the activation energy of acetaldehyde formation. It is found that the activity of all Cu/t-ZrO₂ catalysts grows under the effects of the reaction medium, due to the migration and redispersion of copper.     

Effect of the preparation conditions on the physicochemical and catalytic properties of Ni<Subscript>2</Subscript>P/SiO<Subscript>2</Subscript> catalysts

The effect of the reduction conditions on the physicochemical and catalytic properties of Ni₂P/SiO₂ catalysts was studied. The catalysts were prepared by impregnating silica with a solution of nickel acetate and diammonium hydrogen phosphate followed by drying, calcination, and temperature-programmed reduction. The Ni₂P/SiO₂ catalysts were reduced prior to hydrodeoxygenation (HDO) of methyl palmitate in the catalytic reactor (in situ) at temperatures of 550, 600, and 650 °С for 3 h and at 600 °С for 1 and 6 h. The reduction temperature and reduction time were shown to affect the conversion of methyl palmitate, and the optimal reduction conditions of the Ni₂P/SiO₂ catalysts were found. The Ni₂P/SiO₂ catalyst synthesized according to a widely used preparation method, including steps of passivation and rereduction at 450 °С in addition to the reduction step, is inferior in activity to the samples prepared in situ.     

Catalytic properties of Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in the aqueous-phase reforming of ethylene glycol: Effect of the alumina support

The influence of the alumina support on the catalytic activity of Pt/Al₂O₃ catalysts in aqueous phase reforming of ethylene glycol to hydrogen was studied. The catalysts were prepared by impregnation of γ-, δ-, and α-alumina with H₂PtCl₆. The highest rate of hydrogen production (452 μmol min⁻¹ g⁻¹) obtained with the Pt/α-Al₂O₃ catalyst can be related to the highest extent of dispersion of Pt on α-Al₂O₃. XPS, TEM-EDX and TPR-H₂ measurements showed the absence of chloride-containing surface complexes in the Pt/α-Al₂O₃ catalyst. However, chloride-containing entities were found on the surface of Pt/γ-Al₂O₃ and Pr/δ-Al₂O₃ catalysts. When chloride ions are removed chlorinated Pt species facilitate the sintering of Pt crystallites and in this way affect the extent of Pt dispersion. Moreover, depending upon the particular crystalline form, alumina atoms have different coordination and alumina surfaces contain varying amounts of OH groups of different nature which affect the interaction between Pt and the support.     

Effect of the alkoxides addition order on the properties of Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> catalysts used for methane combustion

A series of Pd/Al₂O₃–ZrO₂ catalysts were prepared to be used in methane oxidation. The effect of the addition order of metal alkoxides on the texture, structure and catalytic properties of the solids is studied. The control of the preparation parameters is achieved via sol gel way as an attractive route of the preparation of these catalysts. N₂ physisorption, XRD, Scanning Electronic Microscopy (SEM) and H₂ chemisorption are the main techniques used to characterize the prepared Pd/Al₂O₃–ZrO₂ catalysts. Textural analysis reveals the mesoporosity of all the catalysts independently of the addition order of alkoxides while surface area is more pronounced when the aluminium alkoxide is added before or with the zirconium precursor. XRD patterns show the development of the zirconia tetragonal phase for all the catalysts. Better metallic dispersion is obtained when aluminium alkoxide is added first which can be justified by the high homogeneity observed on the corresponding catalyst as revealed by SEM technique.     

Thermal stability and catalytic properties of the composite amorphous Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-nanocrystals ZrO<Subscript>2</Subscript>

Catalytic properties in relation to the hydrogen oxidation reaction and thermal stability of materials based on the nanocomposite amorphous Al₂O₃-nanocrystalline ZrO₂ were studied.     

Mechanism of methanol conversion on ZrO<Subscript>2</Subscript> and 5% Cu/ZrO<Subscript>2</Subscript> according to in situ IR spectroscopic data

It is demonstrated by in situ IR spectroscopy that, in methanol conversion on ZrO₂ and 5% Cu/ZrO₂ catalysts, methoxy groups are present on the catalyst surface, which result from O-H or C-O bond breaking in the methanol molecule. Two types of formate complexes, localized on ZrO₂ and CuO, are also observed. The formate complexes form via the oxidative conversion of the methoxy groups. There are two types of linear methoxy groups. First-type linear methoxy groups condense with the formate complex located on CuO to yield methyl formate and then CO and H₂. Second-type methoxy groups appear as intermediate products in the formation of dimethyl ether. The main hydrogen formation reactions are the recombination of hydrogen atoms (which result from the interconversion of surface complexes) on copper clusters and the decomposition of methyl formate. The source of CO₂ in the gas phase is the formate complex, and the source of CO is methyl formate. The effect of water vapor and oxygen the surface reactions and product formation is discussed.     

Study of <Emphasis Type="Italic">n</Emphasis>-hexane isomerization on Pt/SO<Subscript>4</Subscript>/ZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> 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 (CO_ads), 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.     

Influence of the composition of carriers based on ZrO<Subscript>2</Subscript> and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> on the properties of cobalt-containing catalysts on the selective reduction of NO with methane

A series of cobalt-containing granulated and structured catalysts based on zirconium and aluminum oxides has been studied. The optimum composition of binary oxide samples (80% ZrO₂ − 20% Al₂O₃) for the selective reduction of nitrogen monoxide with methane (84% conversion of NO achieved at 320 °C) has been determined. The activity of the structured catalysts depends on both the composition of the secondary carrier (ZrO₂, Al₂O₃, and their mixture) and on the nature of the skeleton of the cellular structure (cordierite, kaolin-aerosil). __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 237–241, July–August, 2007.     

Effect of copper precursors on the catalytic activity of Cu/ZSM-5 catalysts for selective catalytic reduction of NO by NH<Subscript>3</Subscript>

The Cu/ZSM-5 catalysts prepared by different copper precursors were used for the selective catalytic reduction (SCR) of NO _x with NH₃. The Cu/ZSM-5 catalyst prepared by the copper nitrate (Cu/ZSM-5-N) presented the best performance among the Cu/ZSM-5 catalysts and showed above 90 % NO _x conversion at 225–405 °C. The average particle size of CuO was 5.82, 9.20, and 11.01 nm over Cu/ZSM-5-N, Cu/ZSM-5-S (prepared by copper sulfate), and Cu/ZSM-5-C (prepared by copper chloride), respectively. The Cu/ZSM-5-N catalyst showed the highly dispersed copper species, the strong surface acidity, and the excellent redox ability compared with the Cu/ZSM-5-C and Cu/ZSM-5-S catalysts. The Cu⁺ and Cu²⁺ existed in the Cu/ZSM-5 catalysts and the abundant Cu⁺ over Cu/ZSM-5-N might be responsible for the superior SCR activity.     

Binary ZrO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> xerogels: Synthesis and properties

Binary systems of silica and zirconia xerogels have been prepared by hydrolysis of zirconium(IV) oxychloride in the silica gel matrix. Systems of various composition have been studied by ¹H NMR, IR spectroscopy, and thermogravimetry and have been tested in a model process of hydrogen peroxide decomposition. It has been shown that the physicochemical properties of binary oxide systems can be tailored by varying the component ratio.     

Effect of the microstructure of the supported catalysts CuO/TiO<Subscript>2</Subscript> and CuO/(CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>) on their catalytic properties in carbon monoxide oxidation

The effect of the microstructure of titanium dioxide on the structure, thermal stability, and catalytic properties of supported CuO/TiO₂ and CuO/(CeO₂-TiO₂) catalysts in CO oxidation was studied. The formation of a nanocrystalline structure was found in the CuO/TiO₂ catalysts calcined at 500°C. This nanocrystalline structure consisted of aggregated fine anatase particles about 10 nm in size and interblock boundaries between them, in which Cu²⁺ ions were stabilized. Heat treatment of this catalyst at 700°C led to a change in its microstructure with the formation of fine CuO particles 2.5–3 nm in size, which were strongly bound to the surface of TiO₂ (anatase) with a regular well-ordered crystal structure. In the CuO/(CeO₂-TiO₂) catalysts, the nanocrystalline structure of anatase was thermally more stable than in the CuO/TiO₂ catalyst, and it persisted up to 700°C. The study of the catalytic properties of the resulting catalysts showed that the CuO/(CeO₂-TiO₂) catalysts with the nanocrystalline structure of anatase were characterized by the high-est activity in CO oxidation to CO₂.     

Ru/Ni/MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> catalysts for steam reforming of methane: effects of Ru content on self-activation property

The effects of Ru on the self-reducibility of Ru-doped Ni/MgAl₂O₄ catalysts, which do not need pre-reduction treatment with H₂, were investigated in the steam reforming of methane (SRM). The Ru-promoted Ni/MgAl₂O₄ catalysts with various amounts of Ru (0–0.5 wt%) were prepared by stepwise impregnation and co-impregnation methods using hydrotalcite-like MgAl₂O₄ support. For comparison, Ru/MgAl₂O₄ catalysts with the same amount of Ru were also prepared by the impregnation method. The catalysts were characterized by the N₂-sorption, XRD, H₂-TPR, H₂-chemisorption, and XPS methods. Ni/MgAl₂O₄ catalyst in the presence of even the trace amount of Ru (Ru content ≥0.05 wt%) showed higher conversion without pre-reduction as compared to Ru/MgAl₂O₄ catalysts in SRM under the same conditions. The self-activation of Ru–Ni/MgAl₂O₄ catalysts is mainly attributed to the spillover of hydrogen, which is produced on Ru at first and then reduces NiO species under reaction conditions. Besides, Ru doping makes the reduction of NiO easier. The stepwise impregnated Ru/Ni/MgAl₂O₄ catalyst produced superior performance as compared to co-impregnated Ru–Ni/MgAl₂O₄ catalyst for SRM.     

Dispersion state and catalytic properties of vanadia species on the surface of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> catalysts

The dispersion state and catalytic properties of anatase-supported vanadia species are studied by means of X-ray diffraction (XRD), laser Raman spectroscopy (LRS), H₂ temperature-programmed reduction (TPR) and the selective oxidation of o-xylene to phthalic anhydride. The almost identical values of the experimental dispersion capacity of V₂O₅ on anatase and the surface vacant sites available on the preferentially exposed (001) plane of anatase suggest that the highly dispersed vanadium cations are bonded to the vacant sites on the surface of anatase as derived by the incorporation model. When the loading amount of V₂O₅ is far below its dispersion capacity, the dispersed vanadia species might mainly consist of isolated VO_x species bridging to the surface through V-O-Ti bonds. With the increase of V₂O₅ loading the isolated vanadia species interact with their nearest neighbors (either isolated or polymerized vanadia) through bridging V-O-V at the expenses of V-O-Ti bonds, resulting in the increase of the ratio of polymerized to isolated vanadia species and the decrease of the reactivity of the associated surface oxygen anions and, consequently, although the activity increases with loading to reach a maximum value, the turn over number (TON) of the V₂O₅/TiO₂ catalyst decreases linearly. When the loading amount of V₂O₅ is higher than its dispersion capacity, the turn over number decreases more rapidly with the increase of V₂O₅ loading due to the formation of V₂O₅ crystallites in which the oxygen anions associated with V-O-V bonds are less reactive and only partially exposed on the surface.     

Effect of the modification of ZrO<Subscript>2</Subscript>-containing pillared clay with Pt and Cu atoms on the properties of inorganic complex intermediates in the selective catalytic reduction of nitrogen oxides with propylene according to in situ IR-spectroscopic data

It was found that only bridging and bidentate nitrate complexes were formed on the surface of Pt,Cu/ZrO₂-pillared interlayered clay (ZrO₂-PILC) upon the interaction with a flow of the (0.2% NO + 2.5% O₂)/N₂ mixture, whereas monodentate and nitrosyl complexes were not detected. The concentration of nitrate complexes on Pt,CU/ZrO₂-PILC was higher and the strength of their bond to the surface was weaker than those on unmodified ZrO₂-PILC. Isopropoxide and acetate complexes and coordinatively bound acetone were formed on the surface in the interaction of Pt,Cu/ZrO₂-PILC with a flow of the (0.2% C₃H₆ + 2.5% O₂)/N₂ mixture. The supporting of Pt and Cu onto zirconium dioxide pillars resulted in considerable changes in the concentration and the temperature region of the existence of hydrocarbon surface compounds, as compared with ZrO₂-PILC. Under reaction conditions at relatively low temperatures, isopropoxide and nitrate intermediates on the surface of Pt,Cu/ZrO₂-PILC formed a complex structurally similar to adsorbed dinitropropane. At elevated temperatures, a surface nitromethane complex was formed in the interaction of the acetate complex with nitrate species. The spectrokinetic measurements demonstrated that the apparent rate constants of consumption of nitrate and nitroorganic complexes considerably increased on going from ZrO₂-PILC to Pt,Cu/ZrO₂-PILC. Moreover, the constants of consumption of nitroorganic and nitrate complexes were similar for both of the catalysts. This fact suggests that, on the test catalysts, nitroorganic complexes were reaction intermediates in the selective catalytic reduction of NO_x (NO_x SCR) with hydrocarbons. The found differences in the activation species and thermal stabilities of reactants can explain different activities of ZrO₂-PILC and Pt,Cu/ZrO₂-PILC in the SCR reaction of NO_x with propylene in an excess of oxygen.     

Photocatalytic properties of mesoporous TiO<Subscript>2</Subscript>/ZrO<Subscript>2</Subscript> films in gas-phase oxidation of alcohols

We have used the sol-gel template synthesis method to obtain mesoporous zirconium-containing titanium dioxide films and have studied their structural and sorption characteristics, surface acid function, and photocatalytic activity during gas-phase oxidation of aliphatic alcohols. We have shown that the zirconium content changes the acidity and specific surface area of the films, determining the rate at which the studied processes occur and the relative yield of reaction products. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 41, No. 6, pp. 354–359, November–December, 2005.