Selective Oxidation Of Isobutane Research Articles

Time-Varying Flexible Least Squares for Thermal Desorption of Gases

Time-varying linear regression via flexible least squares is used to determine temperature-dependent kinetic parameters during low-pressure, steady-state, temperature-programmed desorption from catalytic surfaces. The flexible least squares approach optimizes time-varying parameters by minimizing dynamic and measurement discrepancies between a linear theoretical model and experimental data using linear regression. The effectiveness of this approach is demonstrated by calculation of accurate temperature-dependent activation energies, preexponential factors, and differential conversion functions for the evolution of 3-methyl-2-oxetanone (β-lactone) during the selective oxidation of isobutane over aluminum phosphomolybdates.

Catalytic activity of V-substituted Cs2Te0.2H0.6 + x PMo12 − x V x O n heteropoly compounds in selective oxidation of isobutane

A series of Cs2Te0.2H0.6 + x PMo12 − x V x O n (x = 0–3) heteropoly compounds has been prepared and tested in the partial oxidation of isobutane. Catalytic tests show that at 350°C very high selectivity to methacrylic acid (60.1%) can be achieved at isobutane conversion of 12.2% over a Cs2.0Te0.2H1.6PMo11VO n catalyst with only one molybdenum atom per unit cell substituted by vanadium. The presence of Te4+ in the heteropoly compounds appears to interfere with the dehydrqgenation step and favor the formation of methacrolein and methacrylic acid.

Effects of Bi on the Catalytic Performance of MoVO/AlPO<SUB>4</SUB> Catalyst for Selective Oxidation of Isobutene

Effects of Bi on the Catalytic Performance of MoVO/AlPO<SUB>4</SUB> Catalyst for Selective Oxidation of Isobutene

Effects of doping Y on crystal structure and catalytic activity of α-Bi2Mo3O12

The single phase Y0·2Bi1·8Mo3O12 and α-Bi2Mo3O12 catalysts have been synthesised by solid state reaction, and the Y0·2Bi1·8Mo3O12 shows better catalytic performance than α-Bi2Mo3O12 in the selective oxidation of isobutene to methacrolein. X-ray powder diffraction structural analysis, X-ray photoelectron spectroscopy and O2 temperature programmed desorption have been used to reveal the effects of doping Y on the crystal structure and catalytic activity of α-Bi2Mo3O12 induced by Y substitution for Bi. It is found that when Bi in α-Bi2Mo3O12 crystal structure is partially substituted by Y with lower electronegativity, the electronic densities of oxygen will increase, which could improve the rate determining α-H abstraction at Bi sites in the selective oxidation of isobutene to methacrolein. On the other hand, the partially regularised MoO4 tetrahedra also promote the catalytic selectivity to methacrolein due to the decrease in oxidation ability. Besides, the longer interatomic distances between Mo3 and Bi in the principal cleavage plane (010) and (010) might result in the lesser catalytic activity of Mo3 sites.

Preparation of Mesoporous Nanosized MoPO-AlPO<SUB>4</SUB> and Its Catalytic Performance for Selective Oxidation of Isobutene

Preparation of Mesoporous Nanosized MoPO-AlPO<SUB>4</SUB> and Its Catalytic Performance for Selective Oxidation of Isobutene

Effect of pH on the Catalytic Properties of Mo–V–Te–P–O Catalysts for Selective Oxidation of Isobutane

Mo–V–Te–P mixed oxide catalysts, prepared by a dry-up method at various pHs (in the range of about 1.0–9.0), have been tested in the partial oxidation of isobutane. The best catalytic performance was achieved over a catalyst prepared at a pH about 7.0. In this case, high selectivity to methacrolein (37.0%) at an isobutane conversion of 12.7% has been obtained at 380 °C. The surface V4+/V5+ ratios of the calcined samples were strongly influenced by the pH in the synthesized solution, which is one of the key factors in the catalytic performance for selective oxidation of isobutane.

Selective oxidation of isobutane over hydrothermally synthesized Mo–V–Te–Sb–O mixed oxide catalysts

A series of MoV0.3Te0.25Sbx (x = 0–0.6) mixed oxide catalysts have been hydrothermally prepared and tested for the partial oxidation of isobutane. XRD results show that a new crystalline phase TeMO (M = Mo, V and Sb) structurally similar to the structure of Te3Mo2V2O17 is formed by incorporation of Sb ions into the Mo–V–Te-based system. Catalytic tests show that very high selectivity to methacrolein (48.6%) can be obtained at 15.1% of isobutane conversion at 390 °C over a hydrothermally synthesized MoV0.3Te0.23Sb0.5 catalyst.

Oxidation of isobutane over hydrothermally synthesized Mo-V-Te-Nb-O mixed oxide catalysts

MoV0.3Te0.17 and MoV0.3Te0.17Nb0.12 catalysts were prepared by a hydrothermal synthesis route and tested for the oxidation of isobutane and isobutene. Characterization results showed that the structure and property of Mo-V-Te-based catalysts are relatively different depending on the presence of the Nb element. Catalytic tests showed that the selectivity of methacrolein can comparatively be improved by the addition of Nb into the MoV0.3Te0.17 catalyst for the selective oxidation of isobutane.

Selective Oxidation of Isobutane and Isobutene to Methacrolein over Te–Mo Mixed Oxide Catalysts

A series of Te–Mo–O catalysts were prepared by decomposing (NH4)4TeMo6O22 · 2H2O telluromolybdate under different conditions and tested for the oxidation of isobutane and isobutene. Characterization results (XRD, FTIR, TG, TPR, XPS, and BET) showed that their structure and properties depend on calcination conditions. Catalytic tests showed that molybdenum may be the key element for the activation of isobutane, whereas the selective oxidation of isobutene to methacrolein (MAL) might proceed mainly on the surface of the TeMo-containing crystalline phase. Thus, relatively high selectivities and yields of MAL and methacrylic acid (MAA) can be obtained over these specially designed catalysts.

Selective oxidation of isobutane over Mo-V-Te mixed oxide catalysts with different tellurium contents

A series of MoV0.3Tex (x = 0−0.3) mixed oxides were prepared and investigated for the selective oxidation of isobutane. Among them, MoV0.3Te0.23 showed the best methacrolein and methacrylic acid selectivity (as high as 17% and 16%, respectively), and the yield to methacrolein and methacrylic acid reached 3.6% and 3.5%, respectively, at 21.3% isobutane conversion at 440°C.

Effect of antimony doping on the catalytic behavior of Mo–V–Te–P mixed oxide catalysts in oxidation of isobutane

Abstract Small amount of antimony addition to a Mo–V–Te–P mixed oxide catalyst strongly affects its catalytic behavior. The antimony which probably enters into the lattice of TeMO (M = Mo, V and P) promotes the oxidative dehydrogenation and selective oxidation of isobutane to isobutylene and methacrolein, and suppresses the further oxidation of methacrolein to methacrylic acid and COx, leading the selectivity to methacrolein to a maximum at Sb/Mo atomic ratio = 0.15. However, further increasing Sb content will decrease isobutane conversion and methacrolein selectivity.

Selective Oxidation of Isobutane to Methacrolein over Mo–V–Te–Sb Mixed Oxide Catalysts with Different Antimony Contents

A series of MoV0.3Te0.23Sb x (x=0–0.6) mixed oxides were prepared and investigated for the selective oxidation of isobutane. Among them, MoV0.3Te0.23Sb0.5 showed the best methacrolein selectivity (as high as 39%), and the yield to methacrolein reached 7.8% at 20.0% isobutane conversion at 470 °C.

Role of the mutual contamination in the synergetic effects between MoO 3 and SnO 2

This contribution is an answer to the criticism that the synergetic effects observed between SnO 2 and MoO 3 in the catalytic dehydration–dehydrogenation of 2-butanol to butene (BUT) and methyl–ethyl–ketone (MEK), in the presence of oxygen and at low temperature (463 K), are not due to a remote control mechanism via the migration of spillover oxygen (Oso) but to the formation of a more active and selective mutual contamination of the oxides during catalysis. Experiments especially designed to artificially induce different types of mutual contamination between SnO 2 and MoO 3 and then to evaluate their catalytic performances have been conducted. Three types of contaminated samples were synthesized: Mo ions deposited at the surface of SnO 2, a solid solution of Mo in SnO 2 lattice and a Sn–Mo–O mixed oxide precursor. The contaminated samples were tested alone and in the presence of SnO 2 and MoO 3. The conclusion is that, for reasons of unstability and/or of low performance, none of the mutual contamination compounds investigated can account for the synergetic effects between SnO 2 and MoO 3. Other experiments conducted with SnO 2 and MoO 3 in the selective oxidation of isobutene at high temperature (693 K) confirm the existence of a synergism between the oxides. In this case, SnO 2 is very active, which induces its continuous reduction during the reaction. To maintain its initial high oxidation level, SnO 2 pumps lattice oxygen from MoO 3. The consequence is that MoO 3 turns progressively reduced. It is shown that an additional supply of Oso succeeds to prevent this phenomenon. Finally, more specific experiments lead to a better understanding of the mechanism by which active sites are formed under the action of Oso. Oso is formed at the surface SnO 2 (which is an Oso donor). It then migrates onto the surface of MoO 3 (which is an Oso acceptor) where it increases the acidity, and thus the dehydration activity, of MoO 3. This accounts for the synergetic increase of the production of BUT observed for mechanical mixtures of SnO 2 and MoO 3.

Rationalization of the Catalytic Behavior of Lanthanide Oxides and Praseodymium Molybdates in Total and Selective Oxidation of Isobutene

The purpose of this work is to examine critically the correlations between ionization potential or absolute hardness and the catalytic behavior of binary and ternary oxides containing lanthanides (Ln) in alkene oxidation. Five lanthanide oxides (La2O3, Sm2O3, Pr6O11, Tb4O7, and CeO2) and three praseodymium molybdates (Pr-2-Mo3O12, Pr6MoO12, and Pr2MoO6, were used as pure phases or in mixtures with MoO3 in the partial and total oxidation of isobutene. The catalytic performances of their mixtures with MoO3 are described in the context of the remote mechanism, according to which the lanthanide-based oxides are identified as donors of spillover oxygen. Their donor ability is evaluated through the synergetic effects on methacrolein selectivity and correlated with the physical properties mentioned above. In the case of ternary oxides such as praseodymium molybdates, the concepts of average ionization energy and average absolute hardness are proposed to take into account the fact that the electron density and therefore the reactivity of mobile surface oxygen species are influenced by the presence of both metals in the lattice. The results obtained with the pure Ln-based oxides are in line with the literature concepts of ionization energy and absolute hardness. As far as the mechanical mixtures are concerned, it is shown that the above correlations, when combined with the remote control concepts, provide a comprehensive view of the influence of ionization energy or absolute hardness for both single phase and biphasic catalysts exhibiting phase cooperation.

Synthesis of methacrylic acid by selective oxidation of isobutane, catalysed by Keggin-type polyoxometalates: relationship between catalytic performance, reaction conditions and chemical–physical features of the catalyst

The ammonium salt of 12-molybdophosphoric acid, (NH4)3PMo12O40 (polyoxometalate, POM), having the Keggin-type structure was prepared and tested as a heterogeneous catalyst for the selective oxidation of isobutane to methacrylic acid. This reaction might represent an alternative to the current industrial process for methyl methacrylate production, the acetone–cyanohydrin process, which is characterized by a no longer acceptable environmental impact. The POM catalyst was found to operate with higher selectivity at isobutane-rich conditions (26 % isobutane, 13 % oxygen), than at isobutane-lean conditions (1 % isobutane, 13 % oxygen). This was attributed to the development of a more favourable distribution of reduced Mo5+ and oxidized Mo6+ sites in the POM in the former case. Modifications occurring in the catalyst during time-on-stream at different reaction conditions are discussed. Version française abrégée — Synthèse d'acide méthacrylique par oxydation sélective de l'isobutane, catalysée par des polyoxométalates du type Keggin ; relation entre les résultats catalytiques et les caractéristiques physico–chimiques du catalyseur. L'oxydation en une étape de l'isobutane en acide méthacrylique est une alternative possible au procédé actuel, assez polluant, de production de méthacrylate de méthyle. Pour cette oxydation sélective, les meilleurs catalyseurs sont les polyoxométallates de type Keggin (POMs), contenant essentiellement du phosphore et du molybdène. L'oxydation sélective de l'isobutane en présence du sel d'ammonium de l'acide 12-molybdophosphorique du type Keggin (NH4)3PMo12O40 a été étudiée dans différentes conditions expérimentales, obtenues en variant le rapport isobutane/oxygène, le temps de réaction et les caractéristiques physico-chimiques des catalyseurs.Pour des rapports isobutane/oxygène élevés, les catalyseurs présentent une période d'activation initiale durant laquelle est observée une augmentation de la conversion de l'isobutane et de la sélectivité en acide méthacrylique de 5 à 40–43 % après 80 h de réaction ; parallèlement, la sélectivité en CO2 diminue.Pour les rapports isobutane/oxygène faibles, si l'activité reste constante (conversion aux environs de 7 %), la sélectivité en acide méthacrylique décroı̂t de 24 % à moins de 5 % dans les mêmes conditions. Ces différences sont expliquées par le fait que, dans des conditions réductrices, avec un rapport isobutane/oxygène élevé, les propriétés physico-chimiques du catalyseur sont modifiées, du fait de la perte du cation ammonium et de la formation de sites Mo+. Ceci est aussi observé, mais de façon beaucoup moins importante, avec des rapport isobutane/oxygène faibles. Pour ces rapports faibles, une réduction préalable du catalyseur entraı̂ne une augmentation de la sélectivité en début de réaction (mais ces améliorations ne durent que quelques heures et sont réversibles). La haute sélectivité observée pour les rapports isobutane/oxygène élevés (conditions réductrices) est attribuée à une plus faible densité de sites oxydants à la surface du catalyseur à l'état stationnaire.

Catalytic behavior of SbRe2O6 in the selective oxidation of isobutene: the key role of the cooperation between Sb4Re2O13 and Re2O7

The catalytic performance of a novel SbRe2O6 compound has been investigated in the selective oxidation of isobutylene to methacrolein at 673 K. The initial reactivity of the catalyst strongly depended on catalyst pretreatment conditions. The catalyst was more active after pretreatments under more oxidative atmospheres. However, the activity of the catalyst always reached an identical level at the steady state, independent of the pretreatment conditions. Scanning electron microscopy and in situ confocal Raman microscopy revealed that the reactivity of SbRe2O6 was attributable to the presence at its surface of Re2O7 which benefitted from a cooperation with Sb4Re2O13. The two phases resulted from a partial decomposition of SbRe2O6 in the presence of oxygen. When deposited on Sb4Re2O13, Re2O7 was stabilized and did not volatilize under the reaction conditions. The phenomenon is likely the origin of the cooperation between Sb4Re2O13 and Re2O7.

Oxidation of isobutane over Mo–V–Sb mixed oxide catalyst

The catalytic performances of Mo–V–Sb mixed oxide catalysts have been studied in the selective oxidation of isobutane into methacrolein. V–Sb mixed oxide showed the activity for oxidative dehydrogenation of isobutane to isobutene. The selectivity to methacrolein increased by the addition of molybdenum species to the V–Sb mixed oxide catalyst. In a series of Mo–V–Sb oxide catalysts, Mo1V1Sb10Ox exhibited the highest selectivity to methacrolein at 440°C. The structure analyses by XRD, laser Raman spectroscopy and XPS showed the coexistence of highly dispersed molybdenum suboxide, VSbO4 and α-Sb2O4 phases in the Mo1V1Sb10Ox. The high catalytic activity of Mo1V1Sb10Ox can be explained by the bifunctional mechanism of highly dispersed molybdenum suboxide and VSbO4 phases. It is likely that the oxidative dehydrogenation of isobutane proceeds on the VSbO4 phase followed by the oxidation of isobutene into methacrolein on the molybdenum suboxide phase.

Solid-state reactivity of iron molybdate artificially contaminated by antimony ions and its relation with catalytic activity in the selective oxidation of isobutene to methacrolein

Catalysts were prepared by impregnation of Fe2(MoO4)3 with different quantities of antimony butoxide. BET surface area measurement, XRD, Mossbauer spectroscopy, CTEM-AEM, XPS and ISS were used to characterize phase and surface architectures and their changes after calcination and catalytic reaction. Before calcination, antimony was present as pure oxide or hydroxide, partly as particles and partly as an incomplete monolayer on the surface of Fe2(MoO4)3. After calcination at 400°C, antimony got detached from the Fe2(MoO4)3 surface and aggregated very intensively, partly as Sb2O4 and partly, through reaction with the iron molybdate, as a mixture of distorted FeSbO4 and MoO3. After reaction or calcination at 500°C, more distorted FeSbO4 and MoO3 are formed, separated from Fe2(MoO4)3. Selective oxidation of isobutene to methacrolein was carried out on the calcined material. Impregnated catalysts show considerably improved catalytic performances compared to the pure Fe2(MoO4)3 phase or mechanical mixtures of it with α-Sb2O4. The catalytic performances are explained by several catalytic cooperations via spillover oxygen. These cooperative effects involve all the oxide phases present in the material having worked as catalyst: Fe2(MoO4)3 (pure or possibly contaminated by small amounts of antimony oxide), FeSbO4, MoO3 and SbyOx.

Evaluation of the role played by bismuth molybdates in Bi 2Sn 2O 7–MoO 3 catalysts used for partial oxidation of isobutene to methacrolein

The catalytic behaviour of multiphasic catalysts based on α-bismuth pyrostannate, Bi 2Sn 2O 7, was investigated in the selective oxidation of isobutene into methacrolein. When α-Bi 2Sn 2O 7 is mixed with MoO 3, strong cooperation effects on the yield and selectivity in methacrolein occur. However, XRD analyses performed on samples after test revealed the formation of a low quantity of α-bismuth molybdate, α-Bi 2Mo 3O 12, when the reaction temperature exceeded 673 K. Additional experiments were therefore carried out on the “Bi–Sn–Mo–O” catalysts in order to shed light on the role of Bi 2Mo 3O 12 in the synergetic effects observed in the Bi 2Sn 2O 7–MoO 3 system. The experimental results are discussed in terms of several hypotheses. First, the intrinsic activity of Bi 2Mo 3O 12 is probably the simplest explanation for the synergetic effects, although experiments have shown that this phase present in a low quantity is only poorly active. Second, catalytic tests made on Bi 2Sn 2O 7–Bi 2Mo 3O 12 mechanical mixtures have evidenced a cooperation between these two ternary oxides, particularly when Bi 2Sn 2O 7 was the major component of the mixture. Consequently, it is likely that a synergy between Bi 2Sn 2O 7 and the in situ generated Bi 2Mo 3O 12 might play a role in the synergy observed in the Bi 2Sn 2O 7–MoO 3 association. Third, as bismuth pyrostannate was previously shown to behave as an oxygen donor phase with respect to WO 3, a remote control mechanism could therefore occur between Bi 2Sn 2O 7 and MoO 3, independently from the formation of α-Bi 2Mo 3O 12.

A Laser Raman Study of Multiphase Co-Bi-Mo Oxide Catalysts

Cobalt and bismuth molybdates catalysts prepared by three different methods (coprecipitation, mechanical mixing and dispersion in n-pentane), have been studied by Laser Raman spectroscopy before and after testing the catalysts in the selective oxidation of isobutene to methacrolein. Raman bands ascribed to the component phases are observed in the spectra before test, while a phase transformation is detected after test.