Formation of the active component of a vanadium-molybdenum oxide catalyst in acrolein oxidation

An acrolein-containing reaction mixture reduces V⁵⁺ to V⁴⁺, accompanied by decomposition of the ammonium salt of vanadium-molybdenum-silicon heteropolyacid (HPA) to form a compound with the tentative composition of VMo₃O_11+x, which is the active component of the catalyst.

---

V⁵⁺ V⁴⁺, VMo₃O_II+X, .

     

Catalytic properties of the vanadium-molybdenum oxide system for acrolein oxidation

The catalytic properties and phase composition of the silica-supported vanadium-molybdenum oxide system have been studied in acrolein oxidation. The active component of the catalyst is the compound VMo₃O_11+x, whose maximum content is observed in the compositions range of 10–15 mol.% V₂O₅ –90–95 mol.% MoO₃.

---

, SiO₂. VMo₃O_11+x, 10–15 .% V₂O₅÷90–85 .% MoO₃.

     

Dynamics of structural transformations in the reduction of copper aluminate

The dynamics of structural transformations during copper aluminate reduction in the temperature range used for catalyst activation was studied by high-temperature X-ray analysis under controlled conditions (hydrogen, 2O–4OO‡C). The techniques of neutron diffraction analysis, IR spectroscopy, chemical phase analysis, and electron microscopy were also used at particular stages. In the course of reduction, copper metal is deposited onto the surface of spinel crystals from the bulk. Spinel becomes cation-deficient with respect to copper. An analysis of powder diffraction patterns demonstrated that copper is reduced and released from tetrahedral positions of the spinel structure at temperatures below ~300‡C and from octahedral positions only at temperatures above 300‡C. In this case, a redistribution of aluminum ions was observed simultaneously. It is likely that the electrical neutrality is attained by the formation of OH groups, the appearance of which in reduced samples was detected by IR spectroscopy and confirmed by neutron diffraction analysis. At a reduction temperature of 400‡C, the oxygen framework was partially disintegrated. The structures of reduced copper aluminates and chromites were compared.     

The effect of the precursor structure on the catalytic properties of the nickel—chromium catalysts of hydrogenation reactions

The influence of the Ni²⁺/Cr³⁺ ratio in the precursor compound on the formation of the catalyst structure and its transformation upon the thermal treatment and reductive activation in hydrogen was studied. The precursors with the cation ratio Ni²⁺/Cr³⁺ = (2.3–3)/1 represent a homogeneous system of the stichtite-type structure. The treatment of the precursors at T ～400 °C in an inert atmosphere forms a nanosized phase of the NiO-type structure with the lattice parameter a = 4.186±0.005 Å. At 600 °C the lattice parameter of this phase decreases to the tabulated value (a = 4.177±0.005 Å). The phase of nickel chromite of the cubic spinel structure with the lattice parameter a = 8.320±0.005 Å is also observed. Hydrogen activation of the catalyst preheated at 300 °C in an inert gas leads to the formation of Ni⁰ crystallites with a size of ～5.5 nm and a specific surface area of ～7.0 m² g^?1. This catalyst exhibits high activity and selectivity in benzene hydrogenation and preferential CO hydrogenation in the presence of CO₂. The catalysts with the ratio Ni²⁺/Cr³⁺ = 1/(2?3) containing nickel and chromium hydroxocarbonates as precursors are less active in the hydrogenation of benzene to cyclohexane.     

Effect of the oxidation state of manganese in the manganese oxides used in the synthesis of Mn-substituted cordierite on the properties of the product

Catalysts based on Mn-substituted cordierite 2MnO · 2Al₂O₃ · 5SiO₂ have been synthesized using different manganese oxides (MnO, Mn₂O₃, and MnO₂) at a calcination temperature of 1100°C. The catalysts differ in their physicochemical properties, namely, phase composition (cordierite content and crystallinity), manganese oxide distribution and dispersion, texture, and activity in high-temperature ammonia oxidation. The synthesis involving MnO yields Mn-substituted cordierite with a defective structure, because greater part of the manganese cations is not incorporated in this structure and is encapsulated and the surface contains a small amount of manganese oxides. This catalyst shows the lowest ammonia oxidation activity. The catalysts prepared using Mn₂O₃ or MnO₂ are well-crystallized Mn-substituted cordierite whose surface contains different amounts of manganese oxides differing in their particle size. They ensure a high nitrogen oxides yield in a wide temperature range. The product yield increases with an increasing surface concentration of Mn³⁺ cations. The highest NO_x yield (about 76% at 800–850°C) is observed for the MnO₂-based catalyst, whose surface contains the largest amount of manganese oxides.     

Structure of MgO-based catalysts modified with Mg(NO3)2 and LiNO3

The structure of magnesium oxide prepared by hydration in lithium nitrate and magnesium nitrate solutions and further thermal treatment is examined by X-ray analysis on a precision diffractometer using synchrotron irradiation. Magnesium oxide with a distorted lattice is formed when this preparation procedure is used, and the symmetry is reduced from cubic to rhombohedral. Distortions were more pronounced in the case of a sample treated with magnesium nitrate. The distortions are due to NO₃ groups incorporated into the oxygen framework of the oxide. Such a structure is stable up to 1000°C. The defects formed lead to the structure and charge inhomogeneity of the crystalline lattice. It is likely that these defects are responsible for the high catalytic activity of the samples.     

Nature of the active component of copper-zinc-aluminium catalyst for methanol synthesis

Comparative studies of the catalytic properties and thermal stability of a copper-zinc-aluminium catalyst and its components have revealed that the catalytic activity is determined by a solid solution of copper and aluminium in zinc oxide containing OH^– and CO ₃ ^2– groups in its anion skeleton. The presence of aluminium in the solid solution ensures the increase of the catalyst thermal stability in the reaction medium.

---

-- , , OH^– CO ₃ ^2– -. .

     

Influence of sodium on the phase composition of bismuth-molybdenum oxide catalysts supported on SiO2

Using an x-ray phase analysis, it has been shown that the application of sodiumstabilized sols to the Bi₂O₃·2.75MoO₃/SiO₂ system leads to the interaction of molybdenum and bismuth oxides with sodium, and the formation of a double Na–Bi-molybdate.

---

, Bi₂O₃·2.75 MoO₃/SiO₂ , , Na–Bi-.