Intergrowth between V2O5 and TiO2 (anatase): High resolution electron microscopy evidence

V₂O₅/TiO₂ (anatase) with 5 and 20 wt.% loadings of V₂O₅ have been studied using high resolution electron microscopy. This has provided the first direct evidence for the formation of a coherent interfacial boundary between two crystalline TiO₂ and V₂O₅ phases. The type of the interfacial stacking was found to be similar for all the samples, whereas the length of the boundary formed depended on the V₂O₅ loading. A model for the atomic arrangement of this boundary based on a comparison of structural positions of oxygen and metal atoms in the crystal lattices of both phases is proposed.     

Catalytic properties of V?Sb?O systems in acrolein oxidation

Catalytic properties of V-Sb-O systems in acrolein oxidation have been studied. It has been established that the changes in the activity and selectivity of the catalysts are due to the phase and chemical properties of the system.

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Formation of vanadia-titania oxide catalysts

The formation of vanadia-titania catalysts was studied with a complex of physicochemical methods. The use of highly dispersed anatase with a defect structure results in the formation of coherent boundaries of coalescence of the V₂O₅ and TiO₂ crystallites with the ratio V : Ti =1 : 1 in a wide range of vanadium and titanium concentrations. The catalysts containing coherent boundaries are active and selective in Β-picoline oxidation to nicotinic acid.     

Localization of the copper-containing component in the pore volume of zeolite ZSM-5

The distribution of the copper-containing component in the pore volume of zeolite ZSM-5 has been investigated by H₂ and N₂ adsorption at 77 K and IR spectroscopy. Samples were synthesized by ion exchange and incipient wetness impregnation. Copper-containing clusters are mostly located on the surface of the mesopores formed by packed zeolite nanocrystallites. This causes partial blocking of the volume of microporous channels for N₂ molecules, but these channels remain accessible for H₂ molecules. It has been deduced that no considerable amount of copper located in the structural channels of the zeolite. According to IR spectroscopic data, the sorption of copper ions in the Cu/ZSM-5 catalysts takes place on extraframe-work aluminum, which forms Al-OH-Al bridges and terminal Al-OH groups, and on terminal Si-OH groups located on the zeolite crystal surface.     

Effect of silica on the stability of the nanostructure and texture of fine-particle alumina

The effect of the modification of aluminum oxide with silicon oxide on the stability of fine-particle Γ- and δ-Al₂O₃ phases upon heat treatment in the wide temperature range of 550–1500°C was studied. It was found that the Γ- and δ-Al₂O₃ phases modified with silica are thermally stable up to higher temperatures than pure aluminum oxide. This is due to changes in the real structure of the modified samples, specifically, an increase in the concentration of extensive defects stabilized by hydroxyl groups bound to not only aluminum atoms but also silicon atoms. It is likely that Si-OH groups, which are thermally more stable than Al-OH groups, stabilize the microstructure of Γ- and δ-Al₂O₃ to higher temperatures, as compared with aluminum oxide containing no additives. Simultaneously, an increase in the thermal stability of the modified samples is accompanied by the retention of a high specific surface area and a developed pore structure at higher treatment temperatures.     

The state of Cu2+ ions in concentrated aqueous ammonia solutions of copper nitrate

Stabilization of Cu²⁺ ions in concentrated aqueous ammonia solutions of copper nitrate in a wide range of ammonium ion concentrations has been studied by EPR and electronic absorption spectroscopy. Three types of Cu²⁺ associates with different types of orbital ordering have been identified. The ammonium ion concentration in a solution has a decisive effect on the type of orbital ordering of Cu²⁺ ions in associates. In all cases, Cu²⁺ ordering in associates is caused by the existence of bridging OH groups in the axial and equatorial positions of [Cu(NH₃) _n (H₂O)_{6 ? n} ]²⁺ complexes (n < 6). At a high concentration of ammonium ions, weakly bound associates of tetramminecopper with the $d_{x^2 - y^2 }$ ground state are formed. In solutions with low ammonium concentrations, bulky associates with the $d_{y^2 }$ and $d_{x^2 - z^2 }$ ground states and associates of Cu²⁺ ions with the $d_{x^2 - y^2 }$ ground state with hydroxyl groups in the equatorial plane and axial water molecules are formed.     

The State of Copper Ions in Aqueous and Aqueous Ammonia Solutions of Copper Acetate

Stabilization of Cu²⁺ ions in aqueous and aqueous ammonia solutions of copper acetate was studied for a wide range of ammonia concentrations. The structure of copper acetate hydrate complexes was shown to markedly change upon dissolution in water. In aqueous solutions, copper is stabilized as strongly bound Cu²⁺ associates (dimers) in a distorted octahedral environment composed of water molecules and acetate groups oxygen atoms in equatorial positions with strong exchange interaction via acetate groups. In solutions of copper acetate in aqueous ammonia, the concentration of ammonia has a crucial effect on the ordering of Cu²⁺ ions in associates. At high ammonia concentration, disordered copper tetra-ammoniate associates with the \({d_{{x^2} - {y^2}}}\) ground state are formed, whereas at low ammonia concentration, bulky Cu²⁺ ion associate structures are generated, with the \({d_{{x^2} - {y^2}}}\) ground state, hydroxyl groups in the equatorial plane, and water molecules in the axial positions.     

HREM Study of Nanostructured Molybdenum and Vanadium Doped Titania Catalysts

MoO₃/V₂O₅/TiO₂ (anatase) catalyst with 5 and 20 wt.% loadings of MoO₃ and V₂O₅ has been studied, using high resolution electron microscopy. Main structural peculiarity of this system was found to be the presence of nanometer size layers of a complex Mo-V-O phase on the surface of the titania support. The observed structure seems to be a metastable and may exist only on the surface of TiO₂ particles.     

Formation of the structure of cerium oxide-modified titanium dioxide

The formation of the structure of titanium dioxide containing 3–15 wt % CeO₂ in a wide temperature range (300–850°C) has been investigated by X-ray powder diffraction, electron microscopy, and adsorption methods. Modification of titanium dioxide with cerium oxide causes the formation of nanostructured Ce-Ti-O compounds consisting of incoherently intergrown fine anatase crystallites. The crystallites are separated by interblock boundaries in which cerium ions are stabilized. The nanostructure formed in the Ce-TiO₂ oxide system stabilizes the anatase phase, prevents the sintering of anatase particles at high temperatures, and allows modified anatase to retain a larger specific surface area and a higher porosity upon heat treatment than pure titanium dioxide does.     

Structure Peculiarities of Reduced Vanadium–Titanium Oxide Catalysts

The properties of vanadium–titanium oxide catalysts, which contain coherent phase boundaries formed by V₂O₅ and TiO₂ crystallites during reduction by hydrogen at 150–500°C, are examined. The phase boundary is preserved over the entire examined temperature range regardless of the structure of vanadium oxide, which is formed. The state of vanadium ions at the phase boundary is determined. The presence of a phase boundary in the catalyst is responsible for the V₂O₅ V₂O₃ transition without the formation of intermediate structures.