Methylpyrazine Ammoxidation over Binary Oxide Systems: V. Effect of Phosphorus Additives on the Physicochemical and Catalytic Properties of a Vanadium–Titanium Catalyst in Methylpyrazine Ammoxidation

Oxide vanadium–titanium catalysts modified by phosphorus additives (20V₂O₅–(80 –n)TiO₂–nP₂O₅, n = 1, 3, 5, 10, and 15 wt %) are studied in methylpyrazine ammoxidation. Two regions of compositions are found corresponding to radically different catalytic properties, namely, catalysts with a low (5 wt % P₂O₅) and high (10 wt % P₂O₅) concentration of the additive. In the first case, the introduction of phosphorus is accompanied by a gradual increase in the activity. In the second case, an increase in the additive concentration results in a decrease in the activity and selectivity to the target product, pyrazineamide, and a simultaneous increase in the selectivities to by-products, pyrazine and carbon oxides. The catalysts are characterized by X-ray diffraction analysis, differential dissolution, IR, and NMR spectroscopic data. As in the binary system, the active sites of the samples with a low concentration of phosphorus contain V⁵⁺ cations in a strongly distorted octahedral oxygen environment, which are strongly bound to a support due to the formation of V–O–Ti bonds. The catalytic properties of the samples containing 10 wt % P₂O₅ are due to the presence of the phase of a triple V–P–Ti compound with an atomic ratio V : P : Ti approximately equal to 1 : 1 : 1. The V⁵⁺ cations in this compound occur in a weakly distorted tetrahedral oxygen environment and are bound to the tetrahedral P⁵⁺ cations.     

Ammoxidation of methylpyrazine over vanadium-titanium catalysts modified by alkali additives

Vanadium-titanium catalysts modified with sodium or potassium additives (1-15 wt.% of Me₂O) have been studied in methylpyrazine ammoxidation. Introduction of the additives results in a decrease in the activity and selectivity of the catalysts due to formation of low-active phase - bronzes (MeV₆O₁₅) and vanadates (α-NaVO₃, KVO₃ and K₃V₅O₁₄). The active sites of the modified samples, similar to those in the V-Ti-O catalyst, are found to be V⁵⁺ cations strongly bound to TiO₂ and located in a significantly distorted octahedral oxygen environment. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ammoxidation of methylpyrazine over binary oxide systems: IV. A vanadia—titania system

The catalytic properties of vanadia-titania catalysts in methylpyrazine ammoxidation are studied. The activity monotonically increases on changing the concentration from pure titania to pure vanadia, and the yield of methylpyrazine passes through a broad maximum corresponding to a V₂O₅ concentration from 10 to 75 wt %. The active sites of binary catalysts contain V⁵⁺ cations in a substantially distorted octahedral environment of oxygen atoms, which are strongly bound to anatase, likely due to the formation of V-O-Ti bonds     

Kinetic Peculiarities in the Low-Temperature Oxidation of H2S on Vanadium Catalysts

H₂S oxidation by oxygen on catalysts V₂O₅/Al₂O₃, V₂O₅/TiO₂, V₂O₅/Al₂O₃/TiO₂ was studied at temperatures below the sulfur dew point. High activity and the oscillation character of the oxidation were demonstrated by catalysts with low contents of V₂O₅ (3–5 wt.%). The increase in the V₂O₅ concentration to 10–20 wt.% results in the reduction of the catalytic activity and oscillation ability. On a pure V₂O₅ catalyst, the oscillations were not detected. The difference between the catalysts with the high and low concentrations of V₂O₅ is explained in terms of the structures of the V⁵⁺ species formed in the catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

Formation of the Pore Structure of Oxide Vanadium–Titanium–Phosphorus Catalysts in the Course of Thermal Treatment

The effect of the conditions of the thermal treatment of vanadium–titanium–phosphorus catalysts on the formation of the pore structure and phase composition was studied. It was found that the optimum doping of catalysts with phosphorus (5 wt % P₂O₅) was favorable for retention of the high dispersity of primary particles up to 450°C. The main change in the texture of the catalysts occurred within the range of micropores and mesopores with D < 10 nm. The formation of the coarsely dispersed well-crystallized phase of a vanadium–titanium–phosphorus compound was detected.     

Racemization of chiral amino alcohols III: Effect of Mg or Ca addition on the activity and stability of the Co/γ-Al2O3 catalyst

The racemization of R-(-)-2-amino-1-butanol in a reaction using Co/γ-Al₂O₃ catalysts and catalysts modified by Mg or Ca was investigated in this paper. Complete racemization was achieved with a yield of over 83% at using the Mg modified Co/γ-Al₂O₃ catalyst under optimized reaction conditions of 170°C and 2.5 MPa of H₂. The catalysts were thoroughly characterized by XRD, XPS, TPR, SEM and TEM. The addition of Mg and Ca may be advantageous for dispersing and stabilizing the active species of the Co/γ-Al₂O₃ catalyst, protecting from sintering, significantly improving its catalytic activity and stability.     

Catalytic reduction of sulfuric acid to sulfur dioxide

The reduction of H₂SO₄ to SO₂ occurs with a relatively good efficiency only at high temperatures, in the presence of catalysts. Some experimental results, regarding conversion of sulfuric acid (96 wt.%) to sulfur dioxide and oxygen, are reported. The reduction has been performed at 800 ?C 900°C and atmospheric pressure, in a tubular quartz reactor. The following commercial catalysts were tested: Pd/Al₂O₃ (5 wt.% and 0.5 wt.% Pd), Pt/Al₂O₃ (0.1 wt.% Pt) and ??-Fe₂O₃. The fresh and spent catalysts were characterized by X-Ray diffraction and BET method. The highest catalytic activity was determined for 5 wt.% Pd/Al₂O₃, a conversion of 80% being obtained for 5 hours time on stream, at 9 mL h^?1 flow rate of 96 wt.% H₂SO₄. A conversion of 64% was determined for 0.5 wt.% Pd/Al₂O₃ and 0.1 wt.% Pt/Al₂O₃. For ??-Fe₂O₃, a less expensive catalyst, a conversion of 61% for about 60 hours was obtained.      

Selective hydrogenation of phenylacetylene on Ni and Ni-Pd catalysts modified with heteropoly compounds of the Keggin type

It is established that unmodified Ni catalysts and Ni catalysts modified with Mo- and W-heteropoly compounds (HPC) of the Keggin type (6 wt %) along with catalyst containing 6% K₄SiW₁₂O₄₀/Al₂O₃ appear to be active in the reaction of phenylacetylene (PA) hydrogenation. At low temperatures (100?C150°C), the selectivity of the process strongly depends on the nature of the modifier or second active metal (Pd). It is demonstrated that in the presence of 6% Ni-0.015% Pd/Al₂O₃ modified by HPC K₄SiMo₆W₆O₄₀, the conversion of PA at 100°C was 87% at a styrene: ethylbenzene ratio of 1: 1. The acidity of HPC is found to influence the side reactions of alkylation and condensation. Transmission electron microscopy demonstrates that Ni in modified HPC 6% Ni/Al₂O₃ is present in the form of the particles below 2 nm in size, and these particles of Ni become larger when affected by the reaction medium during PA hydrogenation.     

A comparative study of Ir/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>, Pt/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>, and Ru/Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in selective hydrogenation of crotonaldehyde

Catalytic performance of gallia-supported iridium catalysts in the reaction of selective hydrogenation of crotonaldehyde in the gas phase was studied and compared to that of platinum and ruthenium catalysts. The best catalytic properties in terms of the selectivity to crotyl alcohol are shown by 5 wt % Pt/α-Ga₂O₃ and 5 wt % Ir/α-Ga₂O₃ catalysts prepared from nonchlorine precursors: Pt(acac)₂ and Ir(acac)₃, but for the 5 wt % Pt/α-Ga₂O₃ a very high selectivity of 75% at the high conversion (ca. 60%) is observed. A high selectivity of galia-supported iridium and platinum catalysts was explained by the surface reducibility of gallium oxide leading to covering (decoration) of platinum and iridium by gallium suboxides and the promoting effect of gallium.     

SYNTHESIS AND PROPERTIES OF POLY(1,6-HEPTADIYNE) HAVING A BULKY AND RIGID t-BUTYLBENZOYL GROUP

The polymerization of 4,4-bis(t-butylbenzoylmethyl)-1,6-hepta-diyne (BTBH) was carried out by group 5,6-transition metal catalysts. MoCl₅- as well as WCl₆-based catalysts were effective for the cyclopolymerization of BTBH. The polymer structure was analyzed to have conjugated backbone and recurring 5-membered ring by various spectroscopes. The polymer showed good solubility in common organic solvents. The polymer had good thermal stability and mechanical property. The oxygen permeability coefficient (PO₂) and permselectivity of oxygen to nitrogen (PO₂/PN₂) of poly(BTBH) with bulky and rigid t-butyl benzoyl group were 23.2 barrer and 4.63, respectively.     

Transformations of cyclohexane and benzene on the bimetallic Ru-Pt oxide catalysts

The bimetallic Ru-Pt/Al₂O₃ catalysts with an overall metal content of 1 wt. % and Pt: Ru weight ratios from 1: 3 to 3: 1 were studied. The catalytic activity for cyclohexane and benzene transformations, including hydrogenation, hydrogenolysis, and skeletal isomerization of the initial substrates and products of intermediate transformations, was studied at temperatures 180–350 °C and H₂ pressures from 1.0 to 5.0 MPa. The maximum yield of n-hexane from cyclohexane and benzene was obtained on the catalysts with a ruthenium content of 0.75–1.0%, being ∼29–30 wt.% at 40% selectivity. The selectivity to form n-hexane decreases with an increase in the cyclohexane conversion and is almost independent of the composition of the Ru-Pt system. On the catalysts under study, benzene is converted to the same products but at temperatures by 60 °C lower as compared to cyclohexane conversion. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 633–637, April, 2006.     

Preparation and characterization of V2O5/MgO catalysts for selective oxidation of 4-methylanisole to anisaldehyde

A series of V₂O₅/MgO catalysts containing 1 to 20 wt % V₂O₅ were prepared and characterized by means of X-ray diffraction, FT-infrared, electron spin resonance, scanning electron microscopy, NH₃ and CO₂ uptake measurements. Activity and selectivity of the catalysts were evaluated for selective oxidation of 4-methylanisole to p-anisaldehyde. Characterization results suggest that the vanadia when impregnated on magnesia interacts strongly with the support and results in the formation of a magnesium orthovanadate compound instead of two-dimensional over layers on the support surface. The V−Mg−O compound formed exhibits good conversion and product selectivity for the title reaction. Attempts are made to correlate the acid-base characteristics of the catalysts, obtained from NH₃ and CO₂ uptakes, with their catalytic properties.     

Synthesis and characterization of poly[4,4-bis(pivaloxymethyl)-1,6-heptadiyne] having high oxygen permselectivity

Cyclopolymerization of 4,4-bis(pivaloxymethyl)-1,6-heptadiyne containing a bulky ester group was examined by group 5,6-transition metal catalysts. Both of the MoCl₅-based and WCl₆-based catalysts were effective for the cyclopolymerization. The obtained polymer was characterized to have planar backbone and recurring cyclic ring structure by various spectroscopy. The poly[4,4-bis(pivaloxymethyl)-1,6-heptadiyne] was soluble in common organic solvents to easily cast the free standing film. The polymer film had good mechanical property and high oxygen permselectivity to nitrogen. The oxygen permeability coefficient (PO₂) and permselectivity of oxygen to nitrogen (PO₂/PN₂) of poly[4,4-bis(pivaloxymethyl)-1,6-heptadiyne] were 19.7 barrer and 5.71, respectively. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4135–4139, 1999     

Catalytic properties of metal-containing oxidized coal catalysts in some redox reactions

An increased activity in some redox reactions was observed for some metal ions bound by ion-exchange to oxidized coals. The similarity of the catalytic properties of oxidized coals modified by Fe(III), Cu(II), Mn(II) and other cations has been established for various redox reactions: decomposition of H₂O₂, oxidation of some organic and inorganic substances by hydrogen peroxide and oxygen. The catalytic activity of the modified coals depends on how the modifying additive is bonded to the surface and the amount of the dopant. New methods for the practical use of catalysts with regulated activity are noted. Translated from Teoreticheskiya i éksperimental’naya Khimiya, Vol. 33, No. 4, pp. 256–260, 1997.     

不同磷含量对NiMoP/Al2O3加氢处理催化剂的影响

采用NiMoP浸渍液浸渍载体γ Al₂O₃制备了不同磷含量的NiMoP/Al₂O₃加氢处理催化剂。为了研究磷对该系列催化剂活性相结构的影响,用二苯并噻吩（DBT）和喹啉为模型化合物,考察了催化剂的加氢脱硫（HDS）和加氢脱氮（HDN）性能。结果表明,添加适当的磷能够提高催化剂的HDS和HDN活性,但是高含量的磷能显著的降低催化剂的催化性能。通过对催化剂进行XRD和HRTEM表征发现,添加磷能够增加MoS2的堆积层数以及Ⅱ型“Ni-Mo-S”相的相对含量,这是因为在制备过程中添加磷降低了活性组分与载体之间的相互作用。     

6-Nitrohexene-1 Metathesis in the Presence of Rhenium Heterogeneous Catalysts

6-nitrohexene-1 (6-NH-1) undergoes metathesis in the presence of 16 wt.% Re₂O₇/Al₂O₃/R₄M and 3 wt.% Re₂O₇/Al₂O₃-SiO₂/R₄M (where R = methyl, ethyl; M = Sn or Pb) catalysts. The system containing alumina as a support is more active. Tetramethyltin (TMT) and tetraethyllead (TEL) used as co-catalysts, exhibited similar activating effect which was greater than with tetraethyltin (TET). The best results were obtained when the Re:Sn(Pb) and 6-NH-1:Re ratios were equal, respectively, to 1:1 and 10:1. The alumina-silica supported catalysts activity can be enhanced by doping the support with very small amounts of molybdenum ions.     

The influence of platinum dispersion on the adsorptivity and reactivity of olefinic alcohols in hydrogenations

Chromium oxides of loading ranges from 5 to 15 wt. % on γ-alumina were tested. The optimum chromium oxide loading for the catalytic oxidation is 10 wt. %. Catalysts were investigated by BET, Raman spectroscopy and XPS. The formation of crystalline Cr₂O₃ has a detrimental effect on catalysts in CH₂Cl₂ oxidation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Oxidative ammonolysis of 3-picoline on mixed oxide catalysts

The oxidative ammonolysis of 3-picoline has been studied on the following catalysts: V₂O₅ on corundum, V₂O₅ with the addition of 1% of H₂WO₄ on corundum, V₂O₅ + MoO₃ + P₂O₅ (1∶0.35∶0.35) on silica gel, V₂O₅ + Al₂O₃, and a melt of V₂O₅ + TiO₂ (1∶0.22). Mixed catalysts of vanadium and titanium oxides exhibited the highest activity and selectivity. With the passage of 25–45 moles of oxygen (in the form of air), 5–10 moles of ammonia, and 50–70 moles of water per mole of 3-picoline at a temperature of 390–410° C, the amount of nicotinonitrile formed on these catalysts amounted to 85–90% of the theoretically possible amount.     

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.