Partial Oxidation Of Isobutane Research Articles

Partial Oxidation of Isobutane and Isobutene to Methacrolein Over a Novel Mo–V–Nb(–Te) Mixed Oxide Catalyst

Aiming at a catalyst with improved catalytic properties in the oxidation of isobutane and isobutene to methacrolein and methacrylic acid, a novel MoVNb(Te) mixed oxide catalyst was synthesized. Rietveld analysis revealed that the crystal structure is well distinguishable from the known MoVTeNb mixed oxide catalyst used in the (amm-)oxidation of C3 hydrocarbons. In the conversion of isobutane, activity as well as selectivities to methacrolein and methacrylic acid were low, and the dehydrogenation of isobutane to isobutene was found to be rate determining. However, the novel catalyst is highly suitable for the partial oxidation of isobutene. While selectivity to methacrolein is comparable to that reported for other catalysts, the activity is superior, resulting in very high space-time-yields at temperatures up to 420 °C. The novel mixed oxide is a Mars van Krevelen-type catalyst. Excess oxygen in the feed is required to ensure optimum performance.

Effect of Different Silicate Supports on the Catalytic Performance of MoVTeO Mixed Oxides in Partial Oxidation of Isobutane

Abstract A series of 5% MoV0.3Te0.25 supported on different silicates (i.e. SiO2, HMS, MCM-41, and MCM-48) have been prepared, characterized, and tested as catalysts in the partial oxidation of isobutane to methacrolein. Characterization results showed that the supports almost kept intact structures after supporting 5 wt.% MoV0.3Te0.25 and the supported catalysts had large specific surface areas. Catalytic tests showed that the specific surface area played a key role in the catalytic activity for the supported catalysts.

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.

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.

Study of Te and V as counter-cations in Keggin type phosphomolybdic polyoxometalate catalysts for isobutane oxidation

Keggin-type phosphomolybdic acid and cesium salts with protons partially substituted by tellurium and by both tellurium and vanadium have been prepared, characterized using several techniques and tested as catalysts in the partial oxidation of isobutane into methacrylic acid (MAA). The results showed that tellurium when introduced as counter-cation was present as Te 4+ capping the Keggin anion and was randomly distributed in the acid or in the cesium salt. This cation induced a positive effect on the selectivity to MAA and methacrolein (MA) without significant effect on the activity except in the acid at low loading where it also increased the activity. The co-substitution of protons by vanadyl cations had a slight effect on the selectivity but increased the activity especially at low level of substitution, which led to a very efficient catalyst. Selectivity to MAA and MA and isobutane conversion rate of 65 and 17% respectively were reached at 350 °C and were both very constant with time on stream. The catalytic results obtained in both stationary and transient conditions allowed to propose a reaction mechanism very close to one already proposed with four intermediates amongst which one is common to both MAA and MA. These results were used to understand the catalytic effect of tellurium and vanadium.

Partial Oxidation of Isobutane Over Hydrothermally Synthesized Mo–V–Te–O Mixed Oxide Catalysts

Mo–V–O and Mo–V–Te–O catalysts were prepared by a hydrothermal synthesis route and tested for the oxidation of isobutane and isobutene. Characterization results (XRD, FT-IR, TPR, BET, and XPS) showed that the structure and property of Mo–V-based catalysts are considerably different depending on the presence of Te element and calcined temperature. Catalytic tests showed that the maximum selectivity of methacrolein (44.2%) can be achieved over a MoV0.3Te0.25-600 catalyst for the selective oxidation of isobutane. It is found that TeMo-containing phases are active and selective for the selective oxidation of isobutane to methacrolein.

The partial oxidation of isobutene and propene on TiO 2(110)

General techniques for the partial oxidation of alkenes by molecular oxygen are a goal for surface science and catalysis research as they may lead to more efficient and environmentally friendly industrial processes. To better understand the thermal surface chemistry of metal oxides toward alkene partial oxidation, the interactions of isobutene and propene on TiO 2(110) were studied using temperature-programmed desorption (TPD). Isobutene was found to adsorb and desorb molecularly below 250 K on the clean surface. With exposure to oxygen (>1000 L) and unknown quantities of water (<10 L), isobutene monolayers on TiO 2(110) react to form products that include methacrolein and isobutanal, as well as a third product that has a C 4H 8O stoichiometry. We tentatively assign this species to 2,2-dimethyloxirane (isobutene oxide). Structural conservation within this family of products points to a common surface intermediate that we propose results from the addition of O from a hydrogen peroxo (HOO) species to the C C bond of isobutene. This hydrogen peroxo (HOO) species forms from the reaction of physisorbed water and oxygen, assisted by partial charge transfer from the TiO 2(110) substrate. Initial studies reveal a similar reaction pathway for the partial oxidation of propene on TiO 2(110), yielding acetone and propanal. This work suggests that TiO 2 surface sites on supported Au/TiO 2 catalysts are active for partial oxidation of alkenes.

The Partial Oxidation of Isobutene in Sub‐ and Supercritical Water

AbstractThe task of this work was to investigate which kind of reaction pathway takes place under supercritical water conditions in the oxidation of isobutene with molecular oxygen. The reaction was examined at temperatures of 350–20 °C, pressures of 25–35 MPa, uncatalyzed and under platinum‐catalyses. Isobutyraldehyde was the main product. Tert‐butanol was used as a source for isobutene, which dehydrates to isobutene quantitatively under the conditions used.

Promotion effects of an extremely low concentration of noble metals supported onto Bi 2Mo 3O 12 on the partial oxidation of iso-butane

Supporting extremely small concentrations of noble metals on SiO 2 and Bi 2Mo 3O 12 affected the catalytic activity and product distribution in iso-butane partial oxidation. Supporting Pt, Pd, and Rh onto SiO 2 by 1 atom/μm 2 enhanced the catalytic activity. Selectivity values of partial oxidation products, iso-butene, CH 3C(CH 3)CHO, CH 3CHO and CH 3COCH 3, were increased and CO x selectivity was decreased. Rh/SiO 2 gave an EPR signal due to isolated Rh 2+ ions with g ⊥=2.07 and g ∥=1.95, suggesting that two valent Rh ions are well dispersed on the surface and play a role in the oxidation of iso-butane. Supporting Pd, Ir, Rh, and Au onto Bi 2Mo 3O 12 at a concentration of (1/9)×10 −4 atom/nm 2 increased the conversion, but supporting Pt and Ru decreased it. Selectivity values of CH 2C(CH 3)CHO and CO x were the same for every catalyst. Catalytic activity was increased by supporting them by (1/49)×10 −4 atom/nm 2; especially, supporting Rh increased the activity without changing the selectivity of CH 2C(CH 3)CHO. Supported noble metal will interact with active oxygen ions bridging Mo and Bi on the Bi 2Mo 3O 12 surface. Since a certain concentration of supported noble metals, (1/49)×10 −4 nm 2, begins to affect the catalytic activity and selectivity, this concentration may reflect the concentration of active sites in iso-butane oxidation at 350–400 °C over Bi 2Mo 3O 12.

Synergic interactions in a urania–titania catalyst for isobutene partial oxidation

The partial oxidation of isobutene has been studied over titania-supported uranium oxide catalysts which exhibit a strong synergy between UOx and support phases.

Partial Oxidation in the Integral Reactor: Possibilities of a Mathematical Description

In this article, it is shown how the kinetics of hydrocarbon oxidation may be described in terms of mathematical equations. The advantages of rather simple and of more elaborate models are compared and discussed. The catalytic gas phase oxidation of butadiene to furan provides the experimental data for the intended examinations. Additional data referring to the partial oxidation of isobutene as well as n-butane will be presented.

Cooperation effects towards partial oxidation of isobutene in multiphasic catalysts based on bismuth pyrostannate

The catalytic behaviour of α-Bi 2Sn 2O 7 was investigated within the framework of the remote control theory. Mixtures of bismuth pyrostannate with typical oxygen donors (Bi 2O 3, Sb 2O 4) or acceptors (MoO 3, WO 3) were therefore prepared and tested in the isobutene–methacrolein conversion at 648 and 673 K. The catalysts were characterized before and after their use by X-ray diffractometry, X-ray photoelectron spectroscopy, scanning electron microscopy and BET specific surface area measurements. The experiments indicate that cooperation for partial oxidation occurs when Bi 2Sn 2O 7 is mixed with acceptor phases. Several mechanisms allowing to explain the synergetic effects observed in the Bi 2Sn 2O 7–WO 3 and the Bi 2Sn 2O 7–MoO 3 mixtures are discussed. In the Bi 2Sn 2O 7–WO 3 catalysts, arguments are presented showing that surface enrichment by one oxide or the in situ formation of a bismuth tungstate phase cannot be reasonably considered as responsible for the cooperation effects. Bismuth stannate is consequently concluded to behave as an oxygen donor with respect to WO 3. Bi 2Sn 2O 7 could “a priori” display the same behaviour in the Bi 2Sn 2O 7–MoO 3 catalysts and cooperate with MoO 3 via a remote control mechanism. But in the latter case, as α-Bi 2Mo 3O 12 is generated in situ, the intrinsic catalytic activity of this bismuth molybdate must probably be taken into account as an additional explanation for the synergy observed in these mixtures. On the other hand, the hypothesis of coverage of one oxide by the other one seems to be ruled out in these Bi 2Sn 2O 7–MoO 3 catalysts.

Catalysis by heteropoly compounds Part 39 The structure and redox behaviour of vanadium species in molybdovanadophosphoric acid catalysts during partial oxidation of isobutane

The states and roles of vanadium of 11-molybdo-1-vanadophosphoric acid (H4PMo11VO40, PMo11V) catalyst in the partial oxidation of isobutane (2-methylpropane) were analysed by EPR, 51V and 31P NMR, IR spectroscopy, and redox titration, and compared with dodecamolybdophosphoric acid (H3PMo12O40, PMo12) catalyst. Thermal treatment of PMo11V at 623 K in O2 caused the elimination of V from the Keggin anion and formed undefined polymeric and a monomeric V species. It was shown based on the redox titration and EPR spectra that the average valency of V in used catalysts significantly changed with the oxygen partial pressure, while that of Mo remained almost unchanged for both PMo11V and PMo12. The selectivities to methacrylic acid (MAA) and methacrolein (MAL) extrapolated to zero conversion were similar for both catalysts, but PMo11V showed a significantly higher selectivity as the conversion increased. This is because the secondary reaction, that is, oxidative decomposition of MAL and MAA, was slower over PMo11V than over PMo12. This was consistent with the marked difference in the reaction order in oxygen pressure, and corresponded to the differences in the above redox properties.

Catalytic reduction of nitric oxide on copper. Part I

The mechanism of NO reduction on copper in the presence of oxygen and isobutene was studied at T = 770 K, under reducing conditions. Mass spectroscopy was used to identify gas-phase intermediates and reaction products. One intermediate species resulting from the partial oxidation of isobutene was shown to be active in the NO conversion. X-ray photoelectron spectroscopy was used to analyze the copper surface at different stages of the reaction. Our conclusion is that oxygen first activates the surface, by forming coexisting phases of Cu 2O and CuO. The copper surface is then reduced by the hydrocarbon, leading to Cu + in majority, and to the formation of an active intermediate. At last, the reduction of NO proceeds rapidly on a zero-valent copper surface together with consumption of the previously formed intermediate. At the end of the reaction, the surface is poisoned by carbon.

Partial oxidation of isobutene to methacrolein on Bi-W/Fe-Co-Mo-K catalysts

The partial oxidation of isobutene to methacrolein and methacrylic acid was studied on oxidic catalysts containing mainly a mixture of bismuth tungstate and iron-cobalt-potassium molybdate. Catalyst shaping was done by extrusion. The kinetic measurements were performed by monitoring the gas-phase composition along the length of a fixed bed of catalyst. The reactor was treated as an isothermal plug-flow system. The network of parallel and consecutive reactions taking place in this system can be described by a simplified scheme. It is possible to predict the gas-phase composition prevailing in the reactor using five different kinetic parameters. In the temperature range 380<ν<420°C grain selectivities as high as 85% combined with yields of methacrolein and methacrylic acid about 72% at 92% conversion were obtained.

Partial oxidation of isobutene over molybdenum trioxide (MoO3)-uranium trioxide (UO3)-silicon dioxide catalysts. A reaction network

Partial oxidation of isobutene over molybdenum trioxide (MoO3)-uranium trioxide (UO3)-silicon dioxide catalysts. A reaction network