Sb Oxide Research Articles

Oxidation of o-Xylene to Phthalic Anhydride on Sb-V/ZrO2 Catalysts

Zirconia-supported and bulk-mixed vanadiumantimonium oxide catalysts were used for the oxidation of o-xylene to phthalic anhydride. X-ray diffraction, Raman spectroscopy and photoelectron spectroscopy were used for characterization. It was found that vanadium promotes the transition of tetragonal to monoclinic zirconia. The simultaneous presence of Sb and V on zirconia at low coverage led to a preferential interaction of individual V and Sb oxides with the zirconia surface rather than the formation of a binary Sb-V oxide, while at higher Sb-V contents the formation of SbVO4 took place. Sb-V/ZrO2 catalysts showed high activity for o-xylene conversion and better selectivity to phthalic anhydride as compared to V/ZrO2 catalysts. However, their selectivity to phthalic anhydride was poor in comparison to a V/TiO2 commercial catalyst. The improved selectivity of the Sb-containing catalysts is attributed to the blocking of non-effective surface sites of ZrO2, the decrease of the total amount of acid sites and the formation of surface V-O-Sb-O-V structures.

Selective methanol conversion to methylal on Re-Sb-O crystalline catalysts: catalytic properties and structural behavior

Three crystalline compounds, SbOReO4·2H2O, Sb4Re2O13 and SbRe2O6, and several supported Re catalysts were employed as catalysts for the selective oxidation of methanol to methylal (3CH3OH+1/2O2 → CH2(OCH3)2+2H2O). A high selectivity of 92.5% to methylal at a conversion of 6.5% under conditions of GHSV = 10000 mL h-1g-1-cat and 573 K was obtained on the new SbRe2O6 catalyst, while no significant formation of methylal was observed with the other two catalysts. No structural change in the bulk and surface of SbRe2O6 and Sb4Re2O13 occurred after methanol oxidation below 593 K, but SbOReO4·2H2O was transformed to Sb4Re2O13, as characterized by XRD, Raman spectroscopy, XPS and SEM. The high performance of SbRe2O6 for the selective methylal synthesis was ascribed to Re oxide species stabilized by a specific connection with Sb oxides at the crystal surface.

Preparation and Properties of Ti/ Sn、Sb Oxide Electrode by the Paste-coating Method

Preparation and Properties of Ti/ Sn、Sb Oxide Electrode by the Paste-coating Method

Niobia-supported Sb–V–O catalysts for propane ammoxidation: effect of catalyst composition on the selectivity to acrylonitrile

The effect of the Sb/V atomic ratio and of the total Sb + V coverage for the ammoxidation of propane to acrylonitrile on niobia-supported V–Sb oxide catalysts is reported. In all cases, acrylonitrile is produced along with propylene and CO2. Depending on the Sb + V coverage two different activity behaviours are reported: below the Sb + V dispersion limit on niobia, the system is predominantly selective to acrylonitrile, this fact has been attributed to exposed Nb centres and to V–Nb–O mixed oxide phases promoted by Sb. At Sb + V loading above monolayer coverage, the system is also selective to acrylonitrile but product distribution is clearly different and characteristic of SbVO4 phases, affording selectivities to propylene similar to those to acrylonitrile.

Oxidation of 2-thiobenzyl-4,6-dimethyl-pyrimidine with hydrogen peroxide over Mo oxides, Mo suboxides and mixed Mo–Sb oxides catalysts

The oxidation of 2-thiobenzyl-4,6-dimethyl-pyrimidine was investigated over catalysts based on MoO 3, Mo suboxides and mixed Mo–Sb oxides to obtain 2-thiobenzyl-4,6-dimethyl-pyrimidine sulfoxide. The chemoselectivity was found to vary with the oxidation state of the Mo atoms, the morphology of the Mo oxide crystals and the concentration of Sb in the structure. The best chemoselectivity (about 80%) resulted from Mo 8O 23. The H 2O 2 efficiency was also found to depend on these parameters. For Mo suboxides the best efficiency was obtained on Mo 8O 23, which suggested that the efficient catalysts are those possessing Mo in a reduced oxidation state. The presence of Sb changed the behavior of the catalysts and the higher H 2O 2 efficiency resulted for the catalysts containing Mo in its highest oxidation state.

The adsorption of toluene on V–Sb oxides. Theoretical aspects

Toluene adsorption reactions on the (1 1 0) surface of VSbO 4 have been analyzed following the changes in the electronic structure of the hydrocarbon molecule and metal cation sites of the oxide using the Just Another Extended Hückel Molecular Orbital Program (JAEHMOP) code. The bonding character of these interactions has also been studied in the same theoretical framework. The calculations indicate that the exothermic hydrocarbon parallel interaction on Sb–V sites results in the weakening of one of the C–H bonds of the methyl fragment. This leads to a H-abstraction that involves the participation of a Sb-cation. Both methyl and phenyl fragments decrease their electronic population and so does the V-cation site. Most of these electrons are transferred to other V atoms in the bulk solid. As a result the LUMO of the toluene–oxide system fully populates. The analysis reveals that methyl–Sb bonding interactions mainly involve C 2p x and H 1s orbitals with Sb 5s orbital, while non-bonding phenyl–V interactions involve C 2p x orbitals with V 3d x 2− y 2 orbital. This last interaction facilitates the desorption of the benzyl species after H-abstraction.

Decomposition of (Ti 2 xFe 1− xSb 1− x)O 4 solid solutions below 1673 K

The pseudo-binary TiO 2–FeSbO 4 system was investigated by means of thermogravimetric analysis below 1673 K in O 2. Rutile-type solid solutions were synthesised at 1373 K in O 2 by means of a solid state reaction between the two pure end members TiO 2 (rutile) and FeSbO 4 mixed in stoichiometric amounts. Thermal stability of the (Ti 2 x Fe 1− x Sb 1− x )O 4 solid solution increases with rutile content; equimolar (Ti 1.00Fe 0.50Sb 0.50)O 4 solid solutions decompose at about 1673 K forming a TiO 2-enriched solid solution and FeSbO 4, that subsequently decomposes into Fe 2O 3 (hematite) and a volatile Sb oxide, probably Sb 4O 6. For compositions characterised by higher Ti content the decomposition temperature is higher than 1673 K.

Effect of Sb/V Ratio and of Sb + V Coverage on the Molecular Structure and Activity of Alumina-Supported Sb–V–O Catalysts for the Ammoxidation of Propane to Acrylonitrile

The effect of the total coverage of Sb + V oxides and the effect of the Sb/V atomic ratio on the ammoxidation of propane to acrylonitrile on alumina-supported V and Sb oxide catalysts is reported. The fresh and used catalysts are characterized by XRD and in situ Raman spectroscopy. Comparison with binary V–Al–O and Sb–Al–O catalysts shows that the presence of both Sb and V oxides strongly enhances the rate of propane ammoxidation to acrylonitrile on alumina-supported Sb–V oxide catalysts. The stability and structural changes during on-stream operation prior to reach steady-state operation originates from a close interaction between Sb and V oxides. The Sb–V interaction depends on total Sb + V coverage on alumina. Below the dispersion limit, SbVO4 phases are not stable under reaction and break into the individual oxides. At Sb + V loading beyond dispersion limit, SbVO4 phases are stable under reaction conditions while Sb and V oxides that did not combine during calcination of the precursor recombine into SbVO4 phases. This solid-state reaction accounts for a higher propane conversion and selectivity to acrylonitrile. Comparison of the performance and molecular structures of fresh and used catalysts further suggests that Sb–V–O phases are necessary for this reaction. The specific formation of acrylonitrile per vanadium site reaches a maximum at an atomic Sb/V ratio of 2. It is likely that a moderate excess of antimony may be necessary for an efficient ammoxidation of propane to acrylonitrile.

Unique Performance and Characterization of a Crystalline SbRe2O6Catalyst for Selective Ammoxidation of Isobutane

The catalytic performances of a new family of crystalline Re−Sb−O compounds SbRe2O6, SbOReO4·2H2O and Sb4Re2O13 in selective ammoxidation of isobutane (i-C4H10) to methacrylonitrile (MAN) have been studied and compared with those of a mechanical mixture of Sb2O3 + Re2O7, coprecipitated SbRe2Ox, Sb2O3-supported Re2O7, bulk Re oxides, and Sb oxides. SbRe2O6 efficiently catalyzed the i-C4H10 ammoxidation to MAN at 673 K with the good selectivity to MAN (44.9%) and to the sum of MAN + i-C4H8 (84.3%) at a steady-state conversion of 4.4%, while significantly no MAN activity was observed on the other catalysts. No structural change in the bulk and surface of SbRe2O6 after the i-C4H10 ammoxidation was observed by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and in situ confocal laser Raman microscopic spectroscopy (LRM). The good performance of SbRe2O6 may be ascribed to its specific crystal structure composed of alternate octahedral (Re2O6)3- and (SbO)+ layers. It was found that the presence of NH3 was prerequisite to the C−H bond breaking of i-C4H10, and the oxidation/dehydrogenation of i-C4H10 never proceeded in the absence of NH3. The presence of NH3 was also prerequisite to maintain the crystal structure of SbRe2O6 under the reaction conditions. Fourier transformed infrared (FT-IR) spectra showed that NHx species irreversibly adsorbed on the SbRe2O6 catalyst. The i-C4H10 ammoxidation proceeded on SbRe2O6 by a redox mechanism, in which the oxidative dehydrogenation of i-C4H10 to i-C4H8 was the rate-determining step. Increasing reaction temperature and decreasing GHSV did not give rise to increase in the formation of byproducts CO2 and acetonitrile. Thus the crystalline SbRe2O6 compound may be regarded to be a new promising catalyst for the ammoxidation of light alkanes.

HREELS and photoemission study of GaSb( [formula omitted])-(1×3) surfaces prepared by optimal atomic hydrogen cleaning

High-resolution electron-energy-loss spectroscopy (HREELS) and synchrotron-radiation photoemission spectroscopy (SRPES) have been used to study the Sb-stabilised GaSb(1 0 0)-(1×3) surface prepared by a two-stage low-temperature atomic hydrogen cleaning (AHC) procedure. The use of a maximum annealing temperature of 300 °C avoids the degradation of surface stoichiometry associated with higher annealing temperatures. After AHC at a sample temperature of 100 °C, SRPES results show that all Sb oxides have been removed and only a small amount of Ga oxide remains. Further AHC treatment at 300 °C results in a clean surface with a sharp (1×3) low energy electron diffraction pattern. SRPES results indicate that the surface stoichiometry is identical to that previously found for GaSb(1 0 0)-(1×3) prepared by in situ molecular beam epitaxy. Electron energy-dependent HREEL spectra exhibit a coupled plasmon–phonon mode which has been used to study the electronic structure of the near-surface region. Semi-classical dielectric theory simulations of the HREEL spectra of the clean GaSb(1 0 0)-(1×3) surface indicate no detectable electronic damage or dopant passivation results from the AHC treatment. Valence band SRPES indicates that the surface Fermi level is close to the valence band maximum, suggesting the presence of an inversion layer at the surface.

Thalcusite from Nakkaalaaq, the Ilímaussaq alkaline complex, South Greenland

Thalcusite from a new locality in the Ilímaussaq complex, the Nakkaalaaq mountain, occurs in a coarse ussingite–aegirine vein and is associated with sphalerite and cuprostibite. The empirical composition is Tl1.89K0.08Cu2.86Fe1.34S4.00. Secondary tenorite–Sb oxide aggregates are developed along cleavages. Tarnish products are essentially pure Cu+ sulphide. All three layered thallium sulphides from the Ilímaussaq complex, thalcusite, chalcothallite and rohaite, contain K substituting for Tl. Varieties with K > Tl were not found in the massif.

Oxidation and ammoxidation of propane over Mo–V–Sb mixed oxide catalysts

Catalytic oxidation and ammoxidation of propane to acrolein and acrylonitrile, respectively, were carried out over Mo–V–Sb mixed oxide catalysts. V–Sb mixed oxide showed the activity for the oxidative dehydrogenation of propane to propene, and the selectivity to propene remarkably increased with increasing the concentration of cation vacancy in VSbO 4 phase. It is likely that the oxidative dehydrogenation of propane on the VSbO 4 phase is initiated via H-abstraction by acid–base concerted mechanism. The selectivity to acrolein and acrylonitrile increased by the addition of molybdenum species to V–Sb mixed oxide catalyst. Among a series of Mo–V–Sb oxide catalysts, Mo 1V 1Sb 10O x exhibited the highest selectivity to acrolein and acrylonitrile at 430 and 480°C, respectively. The highly dispersed molybdenum suboxide was formed together with the both phases of VSbO 4 and α-Sb 2O 4 in the Mo 1V 1Sb 10O x . The high catalytic activity of Mo 1V 1Sb 10O x can be explained by the bifunctional mechanism of the highly dispersed molybdenum suboxide and the VSbO 4 phases as follows: the oxidative dehydrogenation of propane proceeds on the VSbO 4 phase followed by the oxidation of propene into acrolein or the ammoxidation into acrylonitrile on the molybdenum suboxide phase. When large size of MoO 3 crystallites were formed, cracking reaction, i.e., C–C bond cleavage, occurred leading to non-selective total oxidation, resulting in decreasing the selectivities to acrolein and acrylonitrile.

New Photocatalyst Group for Water Decomposition of RuO2-Loaded p-Block Metal (In, Sn, and Sb) Oxides with d10 Configuration

For the decomposition of pure water to hydrogen and oxygen, MIn2O4 (M = Ca, Sr), Sr2SnO4, and NaSbO3 were found to make stable photocatalysts when combined with RuO2. The metal oxides are composed of the d10 p-block metal ions (In3+, Sn4+, and Sb5+), and it is demonstrated that the p-block metal oxides with d10 configuration form a new photocatalyst group different from the conventional metal oxide photocatalyst group consisting of the octahedrally coordinated d0 transition-metal ions such as Ti4+, Zr4+, Nb5+, and Ta5+.

Selective Ammoxidation of Isobutylene to Methacrylonitrile on a New Family of Crystalline Re–Sb–O Catalysts

The catalytic properties of a new family of crystalline Re–Sb–O compounds SbRe2O6, SbOReO4·2H2O, and Sb4Re2O13 in selective ammoxidation of isobutylene to methacrylonitrile (MAN) have been studied and compared with those of a coprecipitated SbRe2Ox catalyst, an Sb2O3-supported Re2O7 catalyst, bulk Re oxides, and bulk Sb oxides. The Re-based catalysts were more or less active for MAN synthesis with selectivities of 47.9–83.6% at 673 K, whereas bulk Sb oxides (Sb2O3 and Sb2O4) showed no activity. The results demonstrate that Re is prerequisite for the ammoxidation catalysis of Re–Sb–O systems. In catalytic systems the presence of Sb also contributes to the ammoxidation catalysis for MAN synthesis. Among these catalysts, SbRe2O6 was most active and selective (83.6%) for MAN formation at 673 K. No structural change in the bulk and surface of SbRe2O6 was observed after i-C4H8 ammoxidation by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and confocal laser Raman microspectroscopy. The good performance of SbRe2O6 may be ascribed to its specific crystal structure composed of alternate octahedral (Re2O6)3− and (SbO)+ layers. Pulse reaction results suggested that adsorbed NH3 species on the SbRe2O6 catalyst facilitated the adsorption and subsequent activation of isobutylene. Increasing reaction temperature and decreasing GHSV did not give rise to increasing formation of by-products CO2 and acetonitrile, while increasing the i-C4H8 conversion. Thus the crystalline SbRe2O6 compound may be a new promising catalyst for ammoxidation of light hydrocarbons.

Chemical Structures of ZrO2-Supported V−Sb Oxides

Fil: Pieck, Carlos Luis. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto de Investigaciones en Catalisis y Petroquimica ; Argentina. Consejo Superior de Investigaciones Cientificas. Instituto de Catalisis y Petroleoquimica; Espana

A crystalline SbRe2O6 catalyst active for selective ammoxidation of isobutylene and propene

This paper reports the first performance of a crystalline SbRe2O6 catalyst, which is a new family of Re mixed oxide, for the selective ammoxidation reactions of isobutylene to methacrylonitrile and propene to acrylonitrile. The SbRe2O6 with alternate (Re2O6)3– and (SbO)+ layers showed much better performance than two other known Re–Sb–O compounds SbOReO4sdot2H2O and Sb4Re2O13 with tetrahedral (ReO4)– anions and cationic (SbO)+ layers. The SbRe2O6 catalyst was also much more active than a coprecipitated SbRe2Ox catalyst, a supported Re2O7/Sb2O3 catalyst, and Re oxides such as Re2O7, ReO3 and ReO2 for the selective ammoxidation. Rhenium is prerequisite to the ammoxidation catalysis of the Re–Sb mixed oxides. Sb oxides such as Sb2O3 and Sb2O4 were inactive, but Sb in the SbRe2O6 catalyst contributes positively to the methacrylonitrile and acrylonitrile syntheses. Neither change nor modification of the surface composition, crystallinity and morphology of SbRe2O6 occurred under the ammoxidation reaction conditions, where the presence of NH3 stabilized the crystalline SbRe2O6 structure.

Thermochemistry and Reactivity of Lattice Oxygen in V–Sb Oxide Catalysts for the Oxidative Dehydrogenation of Light Paraffins

Differential scanning calorimetry is used to study in situthe properties of strongly bound (lattice) oxygen in vanadium-containing supported catalysts for the oxidative dehydrogenation of paraffins C2–C4. Evidence is found that the process occurs via a stepwise redox mechanism with the participation of lattice oxygen from the catalyst. When the supported component is modified by an antimony additive, the amount of reactive oxygen increases and redox processes accelerate. Simultaneously, the rate of coke formation decreases. Additional modification by Bi and Ba leads to a further increase in the amount of reactive oxygen. In all cases, oxygen bound to vanadium atoms is responsible for the redox properties of the systems. The observed effects are analyzed from the standpoint of the ratio between different forms of active oxygen.

Bulk and surface structure and composition of V–Sb mixed-oxide catalysts for the ammoxidation of propane

Vanadium–antimony mixed oxides, which are active and selective catalysts for the ammoxidation of propane to acrylonitrile, were obtained via different preparation routes and studied with a number of bulk and surface-sensitive techniques to elucidate the bulk composition of these complex materials and the character of their exposed surfaces. The V–Sb oxides were prepared via a redox reaction between NH 4VO 3 and Sb 2O 3 in an aqueous slurry, with subsequent calcination, or via a solid-state reaction between Sb 2O 3 and V 2O 5. The characterisation techniques employed were X-ray diffraction (XRD), N 2 physisorption, electron microscopy, potentiometric titration, Mössbauer, EPR, X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), ultraviolet photoelectron spectroscopy (UPS), and IR spectroscopy. It was found that samples obtained by the solid-state reaction were more homogeneous than those prepared via the slurry route. The former consisted of (non-stoichiometric) VSbO 4 for Sb/V=1, or a physical mixture of it with defective Sb 2O 4 for Sb/V=2. Their bulk Sb/V ratio was found also for the surface region, the outmost part of which was enriched in vanadium to a small extent. Materials prepared via the slurry route consisted of (non-stoichiometric) VSbO 4, Sb 2O 4, and V 2O 5 if Sb/V=1; the latter was missing for Sb/V=2 and Sb/V=5. While the character of the mixed surfaces was not determined by the V 2O 5 present, amorphous V oxide structures (highly dispersed species and aggregates) were supported on the Sb 2O 4 surface, which caused a significant vanadium excess in the overall surface composition in samples of Sb/V>1. The average oxidation degree of the surface V species was higher than 4+. Use of these catalysts in the propane ammoxidation reaction caused the surface V oxidation degree to approach 4+ and diminished the degree of surface enrichment in vanadium. This was due both to a disappearance of the dispersed V entities and a decreased detectability of V oxide aggregates (aggregate growth or solid-state reaction with supporting Sb 2O 4). No evidence is available for surface spreading of Sb species as discussed in the literature.

Performance and Characterization of a New Crystalline SbRe2O6 Catalyst for Selective Oxidation of Methanol to Methylal

Three well-defined compounds, SbRe2O6, Sb4Re2O13, and SbOReO4·2H2O, and several supported Re catalysts were employed as catalysts for the selective oxidation of methanol to methylal (3CH3OH+1/2O2→CH2(OCH3)2+2H2O). High selectivity of 92.5% to methylal was obtained on the new crystalline catalyst SbRe2O6 at 573 K, while no methylal formation or negligible activity was observed with the other catalysts. No structural change in the bulk and surface of the SbRe2O6 catalyst occurred after the methanol oxidation below 600 K as characterized by XRD, Raman, XPS, and SEM. The reaction rate increased with increasing methanol partial pressure, while the selectivity to methylal was independent of methanol partial pressure as well as O2 partial pressure (<10 mol%). There existed two types of active lattice oxygen species in TPD experiments on SbRe2O6, both being responsible for the methylal formation. The high performance of SbRe2O6 for the selective synthesis of methylal from methanol may be ascribed to the Re–oxide species stabilized by the specific connection with Sb oxides at the crystal surface.

Selective oxidation of light alkanes over hydrothermally synthesized Mo-V-M-O (M=Al, Ga, Bi, Sb, and Te) oxide catalysts

Selective oxidations of ethane to ethene and acetic acid and of propane to acrylic acid were carried out over hydrothermally synthesized Mo-V-M-O (M=Al, Ga, Bi, Sb, and Te) complex metal oxide catalysts. All the synthesized solids were rod-shaped crystallites and gave a common XRD peak corresponding to 4.0 Å d-spacing. From the different XRD patterns at low angle region below 10° and from the different shape of the cross-section of the rod crystal obtained by SEM, the solids were classified into two groups: Mo-V-M-O (M=Al, possibly Ga and Bi) and Mo-V-M-O (M=Sb, and Te). The former catalyst was moderately active for the ethane oxidation to ethene and to acetic acid. On the other hand the latter was found to be extremely active for the oxidative dehydrogenation. The Mo-V-M-O (M=Sb, and Te) catalysts were also active for the propane oxidation to acrylic acid. It was found that the grinding of the catalysts after heat-treatment at 600°C in N 2 increased the conversions of propane and enhanced the selectivity to acrylic acid. Structural arrangement of the catalytic functional components on the surface of the cross-section of the rod-shaped catalysts seems to be important for the oxidation activity and selectivity.