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  • 1
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract Исследовали окислительное аммонирование различных галогензамещенных толуолов на кристаллических катализаторах фосфата ванадия. Использованные монофосфаты и NH4VOP2O7 превращены в новые V-P окислы, содержащие NH4. Использованные (VO)2P2O7 оказались стабильными во времени и на потоке. ЭТИ соединения являются очень активными и селективными катализаторами окислительного аммонирования.
    Notes: Abstract The ammoxidation of various halogen-substituted toluenes on crystalline vanadium phosphate catalysts was investigated. The monophosphates and the NH4VOP2O7 are transformed into new NH4-containing V-P-oxides. The (VO)2P2O7 used is stable in time on stream. These structures are very active and selective ammoxidation catalysts.
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  • 2
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract Исследовали парофазное окисление 4-пиколина до пиридин-4-карбоксиальдегида на (VO)2P2O7. Предшественником катализатора служил VOHPO4·0,5H20. Образующийся альдегид ловили в виде оксима с помощью раствора гидрохлорида гидроксиламина. В оптимальном интервале температур (683–703 К) была достигнута высокая конверсия 4-пиколина с хорошей селективностью к альдегиду.
    Notes: Abstract The vapor-phase oxidation of 4-picoline to pyridine-4-carboxaldehyde on (VO)2P2O7 has been studied. VOHPO4·0.5 H20 was used as catalyst precursor. The resulting aldehyde was trapped as oxime with hydroxylamine hydrochloride solution in a subsequent reaction. In the optimum temperature range (683–703 K), a high 4-picoline conversion with good selectivity for the aldehyde was observed.
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  • 3
    ISSN: 1572-879X
    Keywords: faujasite-hosted rhodium ; in situ FTIR spectroscopy ; CO hydrogenation ; rhodium dispersion ; methanol selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In situ FTIR spectroscopy has been applied to study the reason of the different selectivity behaviour of rhodium in the CO hydrogenation reaction in dependence on the different particle size. Several forms of molecularly adsorbed CO are observed, such as linearly- and bridgedbonded CO on metallic rhodium as well as dicarbonyl species with Rh(I) centres formed by oxidation of Rh(0) with protons in presence of CO. Furthermore, non-reactive formate, acetate, and carbonate species are produced as side products of the reaction. The higher selectivity to oxygenates, particularly to methanol, is explained by the existence of multiple-bonded CO present only on small rhodium crystallites. The multiple-bonded CO formed at low temperatures is converted at higher temperatures to the highly reactive formyl species, which is hydrogenated to methanol.
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  • 4
    ISSN: 1572-879X
    Keywords: Alkali zeolites ; acid zeolites ; proton exchange ; phase selectivity ; methylated amines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract T-zeolites with different H+-exchange degrees (0, 44, 68 and 89%) were used for the amination of dimethyl ether in the temperature range of 603 to 703 K. On a Na, K-T-zeolite sample (synthesis form) at low dimethyl ether conversion high selectivities of lower methylated amines were observed and methanol was formed as by-product. By proton exchange the conversion could be enlarged, but the selectivity distribution was shifted to trimethylamine.
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  • 5
    ISSN: 1572-879X
    Keywords: Dimethylether amination ; methylamines ; zeolite T ; acidic properties ; TPDA ; IR spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Freshly prepared and used H/Na, K-T-zeolite catalysts for the conversion of dimethyl ether and ammonia to the three methylamines have been characterized by temperature-programmed desorption of ammonia and IR spectroscopy. Activity and selectivity depend on the nature and number of the acid sites. With time on-stream, deep alterations in the catalyst behaviour have been observed. The activity of the catalyst is decreased by blocking of active sites ≈ 5–10 h: furthermore, during an initial period hydrocarbons were formed almost exclusively on strong-acid sites. A second period is characterized by an increased “shape selectivity” observed in the distribution of the methylamines. The amination will proceed probably on left weak-acid sites and on the outer surface in a third period, however, without “shape selectivity” due to the progressive blocking of the inner catalyst surface.
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  • 6
    ISSN: 1572-879X
    Keywords: Iridium catalyst ; supported catalyst ; vapor-phase carbonylation ; methanol carbonylation ; active carbon support
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Iridium on active carbon (Ir/A.C.) is an effective catalyst for the vapor-phase carbonylation of methanol. In contrast to rhodium-catalysts the reaction rate is nearly independent of the partial pressure of the methyl iodide promoter and the methanolysis of an iridium-acetyl species has been found to determine the rate. Undesired methane formation accompanying the carbonylation is suggested to proceed via proteolysis of iridium-methyl species by methanol or water. Methyl chloride has been found to be a less effective promoter than methyl iodide.
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  • 7
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the synthesis of p-hydroxybenzonitrile as a herbicide intermediate the nitrile formation is the most important reaction step. Possible feed compounds could be pure p-cresole, cresole mixtures or OH-protected cresoles like methoxy- or acetoxytoluenes. The ammoxidation of m- and p-methoxytoluene and a m,p-methoxytoluene-mixture over vanadium-titanium oxide catalysts has been investigated using flow reactors in a temperature range of 630-703 K. On comparable reaction conditions the conversion of pure compounds leads to a higher selectivity of p-methoxybenzonitrile (approx. 70%, conversion 85 mol-%) than that of the m-compound (only 35%, conversion 45 mol-%). For synthesis of the p-nitrile the feedstock can be p-methoxytoluene obtained by methylation of p-cresole, but it is also possible to use a m,p-methoxytoluene mixture obtained by methylation of an industrial cresole mixture. The ammoxidation of such a mixture affords a higher reactivity of the p-isomer and p-methoxybenzonitrile as the main reaction product, whereas m-methoxytoluene remains unreacted for the most part. Generally, the results obtained show that an amount of approx. 79% of the converted p-methoxytoluene was transformed into p-methoxybenzonitrile, whereas the corresponding transformation into the m-isomer was lower than 36%. An important part of the m-isomer was degraded by oxidation towards CO, CO2 and HCN.
    Additional Material: 2 Ill.
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  • 8
    ISSN: 1572-879X
    Keywords: Faujasite X hosted rhodium ; rhodium particle size ; IR-spectroscopy ; TEM ; CO hydrogenation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Different metal dispersions of Na-faujasite X hosted rhodium were generated and characterized by transmission electron microscopy (TEM) and IR-spectroscopy. CO hydrogenation has been studied over these Rh/NaX-zeolite catalysts. The finer rhodium dispersion with a mean particle size of 1–2 nm shows a higher selectivity towards oxygenates (methanol, ethanol and dimethyl ether) as compared to the coarser dispersion (4–5 nm), where nearly exclusively methane and higher hydrocarbons are formed.
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  • 9
    ISSN: 1572-879X
    Keywords: vanadyl pyrophosphate ; partial oxidation of toluene ; in situ spectroscopy ; reactant–catalyst interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Vanadyl pyrophosphate catalysts were generated by dehydrating VOHPO4·(1/2)H2O at different temperatures and duration of the dehydration procedure. The as-synthesised materials were characterised by X-ray diffractometry, FTIR spectroscopy and temperature-programmed reduction. The prolongation of the formation period at higher temperatures led to improved crystallinity and lower BET surface areas of the vanadyl pyrophosphate specimens and, additionally, a significantly impeded reducibility of the vanadyl sites was observed. The catalytic performance of the samples was tested in the partial oxidation of toluene to benzaldehyde. The obtained results revealed an increasing benzaldehyde selectivity with improved catalyst crystallinity. In situ FTIR and ESR spectroscopy were used to throw more light on the interaction of the toluene–air feed with the surface of the catalyst.
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  • 10
    ISSN: 1572-9028
    Keywords: ammoxidation ; vanadium phosphate catalysts ; catalyst/feed interaction ; reaction mechanism ; FTIR spectroscopy ; TAP technique ; isotope experiments ; TPD ; TPRS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The reaction pathway of the ammoxidation of toluene on (VO)2P2O7 used as catalyst and the interaction of potential intermediates with the pyrophosphate were studied by spectroscopic techniques (FTIR, EPR), temperature-programmed chemisorptions/ reactions (TPD, TPRS) and transient studies such as the temporal analysis of products (TAP) technique. NH3 is chemisorbed on the catalyst surface, forming three different species, i.e., NH 4 + ions located on BrØnsted sites, coordinatively bound NH3 on Lewis sites and NH 2 − groups, presumably P-NH2. Toluene that is probably adsorbed on Lewis sites reacts in a first step to a benzyl radical. A subsequent partial oxidation by interaction of VIV=O groups generates a V...O=CH-C6H5 surface structure. This benzaldehyde-like surface species reacts with adsorbed NH3 according to a Langmuir-Hinshelwood mechanism. TAP experiments on ammonium-containing vanadium phosphates revealed that NH 4 + ions could act as potential N-insertion species. No formation of benzylamine as well as the generation of V=NH surface groups as possible intermediates or N-insertion sites were observed.
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