878 research outputs found
Vanadium/phosphorus mixed oxide from the precursor to the active phase:Catalyst for the oxidation of n-butane to maleic anhydride
No full textThis review examines the recent scientific and patent literature dealing with V/P/O-basedcatalysts for the synthesis of maleic anhydride by n-butane oxidation. Attention is focused on the different methods of preparation claimed by each company, as well as on the main parameters in precursor preparation and thermal treatment affecting the final catalytic performance. The role of the various promoters reported in the literature is also discussed. © 1995 Elsevier B.V
Oxidation of 1-Butene and Butadiene to Maleic Anhydride. 2. Kinetics and Mechanism
No full textThe kinetics of the oxidation of 1-butene and butadiene over a vanadium-phosphorus mixed oxide catalyst prepared
by reduction of V,O, in an organic medium were investigated. Increased 1-butene concentration in the feed strongly
inhibited the rate of maleic anhydride formation but did not affect the rate of formation of the other products (methyl
vinyl ketone, crotonaldehyde, acetaldehyde, and carbon oxides). The inhibition was interpreted by a Langmuir-
Hinshelwood type model where the ratedetermining step is the reaction between adsorbed oxygen and the
intermediate butadiene adsorbed on two adjacent sites. The rates of formation of the other byproducts are
interpreted by expressions which correspond to the reaction between 1-butene or butadiene adsorbed on one site
and adsorbed or gaseous oxygen. Satisfactory fit of the derived rate expression with the experimental data was
obtaine
Key aspects of catalyst design for the selective oxidation of paraffins
No full textThis review examines some aspects in the development of heterogeneous catalysts for the oxyfunctionalization of light paraffins. Particular attention is devoted to the reaction of paraffin oxydehydrogenation to olefins and of -butane oxidation to maleic anhydride. Most catalyst compositions are based on vanadium oxide as the main component, and the peculiar properties of this element with respect to the catalytic performance are discussed. These properties are also examined in light of the stability of the product of partial oxidation towards consecutive unselective oxidation reactions, and with respect to the mechanism of paraffin activation
Oxidation and Ammoxidation of Toluene Over Vanadium Titanium-oxide Catalysts - A Fourier-transform Infrared and Flow Reactor Study
No full text“Remote laboratory: how to render less virtual as possible the meet with the instrumentation”
No full textNature of vanadium species in SnO2 - V2O5-based catalysts. Chemistry of preparation, characterization, thermal stability and reactivity in ethane oxidative dehydrogenation over V-Sn mixed oxides
No full textTin-vanadium mixed oxides have been prepared either from V4+-Sn4+ solutions by coprecipitation, or by the solid-state reaction between SnO(OH)2 and V2O5, and characterized by means of chemical analysis, FTIR spectroscopy, EPR, X-ray diffraction and surface area measurements. Interaction between the hydroxy groups of the tin oxohydrate and the vanadium ions, reduction of V5+ ions to V4+ and stabilization inside the rutile structure led to the formation of a VxSn1-xO2 solid solution after calcination at 700 °C. A maximum amount of 10 atom% of vanadium entered the SnO2 lattice; at values of up to x = 0.02, V4+ was likely to be homogeneously dispersed, while higher amounts probably formed V4+ oxide clusters inside the rutile matrix. In addition, amorphous V5+ oxide was formed over the rutile surface, and at an overall vanadium content greater than 20-25 atom% crystalline V2O5 was also formed. In samples where x ≥ 0.02-0.03, the solid solution was not stable at temperatures greater than 700 °C, and some of the V4+ was released from the structure forming segregated amorphous V5+ oxide, while for x < 0.02 the solution was stable. The V-Sn mixed oxides were tested as catalysts for ethane oxidative dehydrogenation. The catalysts initially exhibited an unstable behaviour due to a reduction of the V5+ oxide in the reaction environment. Tin oxide activity was enhanced by the addition of V4+; for x = 0.018, also the selectivity to ethene at temperatures higher than 480 °C was significantly greater. In contrast, selectivity to ethene at low temperatures was lower for x > 0.018
Catalytic properties of iron-based mixed oxides in the oxidation of methanol and olefins
No full text"On the chemistry of vanadium-phosphorus oxides. Note V: Crystallogenesis of vanadyl hidrogen phosphate"
No full text
NATURE OF VANADIUM SPECIES IN SNO2-V2O5-BASED CATALYSTS - CHEMISTRY OF PREPARATION, CHARACTERIZATION, THERMAL-STABILITY AND REACTIVITY IN ETHANE OXIDATIVE DEHYDROGENATION OVER V-SN MIXED OXIDES
No full textTin-vanadium mixed oxides have been prepared either from V4+-Sn4+ solutions by coprecipitation, or by the solid-state reaction between SnO(OH)(2) and V2O5, and characterized by means of chemical analysis, FTIR spectroscopy, EPR, X-ray diffraction and surface area measurements. Interaction between the hydroxy groups of the tin oxohydrate and the vanadium ions, reduction of V5+ ions to V4+ and stabilization inside the rutile structure led to the formation of a VxSn1-xO2 solid solution after calcination at 700 degrees C. A maximum amount of 10 atom% of vanadium entered the SnO2 lattice; at values of up to x = 0.02, V4+ was likely to be homogeneously dispersed, while higher amounts probably formed V4+ oxide clusters inside the rutile matrix. In addition, amorphous V5+ oxide was formed over the rutile surface, and at an overall vanadium content greater than 20-25 atom% crystalline V2O5 was also formed.In samples where x greater than or equal to 0.02-0.03, the solid solution was not stable at temperatures greater than 700 degrees C, and some of the V4+ was released from the structure forming segregated amorphous V5+ oxide, while for x < 0.02 the solution was stable. The V-Sn mixed oxides were tested as catalysts for ethane oxidative dehydrogenation. The catalysts initially exhibited an unstable behaviour due to a reduction of the V5+ oxide in the reaction environment. Tin oxide activity was enhanced by the addition of V4+; for x = 0.018, also the selectivity to ethene at temperatures higher than 480 degrees C was significantly greater. In contrast, selectivity to ethene at low temperatures was lower for x > 0.018
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