Oxidation Of Isobutane Research Articles

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.

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.

Effect of calcination conditions on the catalytic behavior of Te-Mo mixed oxide catalysts in oxidation of isobutane and isobutene

A series of Te-Mo-O catalysts were prepared by decomposing (NH4)6TeMo6O24·nH2O telluromolybdate under different conditions and tested for the selective oxidation of isobutane and isobutene. Characterization results showed that their structure and properties depend on the 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 might proceed mainly on the surface of a TeMo-containing crystalline phase.

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.

Partial Oxidation of Isobutane over Vanadium Phosphorus Oxides

A series of vanadium phosphorus oxides (VPO) were prepared by using dodecyl amine as surfactant and tested for the partial oxidation of isobutane and isobutene. Characterization results showed that their structure and properties depend on the content of dodecyl amine. Catalytic tests showed that relatively high isobutane conversion and desired product selectivity can be achieved over a proper dodecyl amine doping VPO catalyst. It is also found that higher isobutane conversion can be achieved over V4+-containing phases as compared to V5+-containing phases, while proper surface V5+/V4+ ratio may be propitious to obtain high selectivity to methacrylic acid for the selective oxidation of isobutane. In addition, the content of dodecyl amine in the preparation of the VPO catalysts appears to be more important in determining the surface P/V ratio of the catalysts.

Oxidation of isobutane and isobutene to methacrolein over hydrothermally synthesized Mo–V–Te–O mixed oxide catalysts

Abstract A series of Mo–V–Te–O catalysts were prepared by calcining the hydrothermally synthesized MoV0.3Tex (x = 0–0.4) precursors and tested for the selective oxidation of isobutane and isobutene. Characterization results showed that their structure and properties depend on the composition of the prepared samples. Catalytic tests showed that relatively high conversion of isobutane (15.6%) and selectivity to methacrolein (44.2%) can be achieved over a MoV0.3Te0.25 catalyst. It is found that TeMo-containing phases are active and selective for the selective oxidation of isobutane to methacrolein.

Kinetics and Mechanism of Catalytic Partial Oxidation Reactions of Alkanes on Rhodium Surfaces

The kinetics of the partial oxidation of isobutane with molecular oxygen on Rh(111) single-crystal surfaces were studied by using a collimated molecular beam under ultrahigh vacuum conditions. Both hydrogen and water were shown to form as primary products, not after secondary reforming or water-gas shift steps as it has been suggested in the past. The production of carbon monoxide (but not of carbon dioxide) was also detected. Water production reaches its steady-state rate in a slower fashion than the rest of the products, presumably because of the kinetics of formation and consumption of the hydroxo surface intermediate involved.

Shock tube and modeling study of isobutene pyrolysis and oxidation

Pyrolysis and oxidation of isobutene were studied behind reflected shock waves in the temperature range 1000–1800K at total pressures between 1.0 and 2.7atm. The study was carried out using following method: (1) a single-pulse technique for product yields, (2) time-resolved IR-laser absorption at 3.39μm for isobutene decay and formation rates of compounds which contain C–H bond, (3) time-resolved IR emission at 4.24μm for CO2 formation rate, and (4) time-resolved UV absorption at 306.7nm for OH radical formation rate. The pyrolysis and oxidation of isobutene were modeled using a reaction mechanism including the sub-mechanisms for methane, acetylene, ethylene, ethane, formaldehyde, allene, propyne, propene, and ketene oxidation. The reaction mechanism used in the present study could reproduce all experimental results.

Selective oxidation of isobutane and isobutene over vanadium phosphorus oxides

Abstract Vanadium phosphorus oxide (VPO) was prepared by using dodecyl amine as surfactant and tested for the oxidation of isobutane and isobutene. Characterization results (BET, XRD, EPR, and XPS) showed that the structure and property of the VPO catalyst prepared by using dodecyl amine as surfactant is considerably different in comparison with the VPO catalyst synthesized without dodecyl amine. Catalytic tests showed that relatively high isobutane conversion and desired product selectivity can be achieved over dodecyl amine doping VPO catalyst. It is also found that proper surface V 5+ /V 4+ ratio may be propitious to obtain high selectivity to methacrylic acid for the selective oxidation of isobutane.

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.

Selective Oxidation and Oxidative Dehydrogenation of Isobutane over Hydrothermally Synthesized Mo–V–O Mixed Oxide Catalysts

A series of Mo–V–O catalysts were prepared by calcining the orthorhombic (M1) Mo–V–O phase containing precursors under different conditions (T = 500 or 600 °C in atmosphere of N2 or air) and tested for the oxidation of isobutane and isobutene. Characterization results (BET, XRD, XPS, FTIR, and TPR) showed that their structure and properties depend on the composition of the calcined samples and the calcined conditions. Catalytic tests showed that relatively high isobutane conversion and desired product selectivity can be achieved over MoV0.3-500-N and MoV0.3-600-A catalysts. It is also found that both orthorhombic M1 phase and (V0.07M0.93)5O14 phase are active and selective for the selective oxidation of isobutane to methacrolein, whereas higher selectivity toward methacrolein (40.4%) can be achieved over the former phase at a moderate isobutane conversion (6.4%). Moreover, (Mo0.3V0.7)2O5 phase may be propitious to complete oxidation for the selective oxidation of isobutane. On the other hand, the presence of V affects the activity and selectivity, and a low surface V4+ concentration prefers selective oxidation products. In addition, specific surface areas of the catalysts appear to be little important in determining the catalytic activation.

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.

Anaerobic oxidation of isobutane

Abstract The anaerobic oxidation of isobutane over complex oxide catalysts of the type CunV2Ox (n = 0, 1, 2, 3, and 5) was studied. V2O5, CuV2O6, and Cu2V2O7 showed high oxidizing activity, and Cu3V2O8 and Cu5V2O10 were less active. Over the active catalysts, CO2 was selectively formed only at the beginning of the reaction, and the rate of CO2 formation decreased with reaction time. Isobutene formation became dominant 15–30 min after the start of the reaction. The rates of CO2 and isobutene formation were lower over the less active catalysts, Cu3V2O8 and Cu5V2O10. The catalytic activity at 623 K decreased in the order V2O5 > CuV2O6, Cu2V2O7 ≫ Cu3V2O8, Cu5V2O10. Because CO2 formed at the beginning of the reaction, this system should be applicable for the selective formation of isobutene at appropriate reduction degrees. We concluded that CuV2O6 and Cu2V2O7 should be applicable in a thin-layer reactor, in which isobutane and oxygen are separately supplied to opposite sides of the layer; in such a reactor, the catalyst surface on the isobutane side could be kept at a certain degree of reduction. Using the rate constants for isobutane consumption over Cu2V2O7, we calculated the apparent activation energy for anaerobic oxidation of isobutane to be 87.6 kJ/mol, which agrees well with the reported value for a metal oxide catalyst. XPS analysis indicated that not V5+ but Cu2+ was reduced during the reduction of Cu2V2O7 by H2 at 473 K. Our results indicate that selective oxidation should be achievable over complex oxides that contain highly redox-active metal ions such as Cu2+ if the reaction is carried out in a thin-layer reactor.

Selective oxidation of isobutane on V-Mo-O mixed oxide catalysts

Four V-Mo-O mixed metal oxides were prepared, characterized and tested for the selective oxidation of isobutane in the temperature range 350-550?C, at atmospheric pressure. Isobutane was mainly oxidized to isobutene and carbon oxides. The systems with low vanadium contents showed low activities but high isobutene selectivities, while the systems with high vanadium contents showed high activities with high carbon oxides selectivities. The effects of temperature, contact time and the molar ratio iso-butane to oxygen on the conversion of isobutane and the selectivity of the oxidation were studied.

Accurate low-pressure kinetics for isobutane oxidation over phosphomolybdic acid and copper(II) phosphomolybdates

A low-pressure steady-state technique has been used to investigate the rates and mechanisms of the oxidation of isobutane over H 3[PMo 12O 40], CuH 4[PMo 12O 40] 2, Cu 2H 2[PMo 12O 40] 2, Cu 2.5H[PMo 12O 40] 2, and Cu 3[PMo 12O 40] 2. Observed oxidation products over all catalysts are methacrolein, 3-methyl-2-oxetanone, acetic acid, carbon dioxide and water. The most selective catalyst for methacrolein formation at low temperatures (<496 °C) is Cu 2.5H[PMo 12O 40] 2, where both Cu(II) reduction and acid sites play a role. The least active catalyst at low temperatures is phosphomolybdic acid followed by Cu 3[PMo 12O 40] 2. This activity is reversed at higher temperatures. The 3-methyl-2-oxetanone is a unique product and is likely to be the precursor to methacrylic acid. Acetic acid is also probably a precursor to complete oxidation. Catalyst deactivation or restructuring is significant only over H 3[PMo 12O 40].

Anaerobic oxidation of isobutane: Catalytic properties of MgV 2O 6 and Mg 2V 2O 7 prepared by the molten method

The catalytic activity of MV 2O 6 and M 2V 2O 7 type oxides prepared by the molten method (MM) for anaerobic oxidation of isobutane was studied in order to construct a system for the selective oxidation of isobutene using a thin layer reactor. Isobutene, CO and CO 2 were formed by every catalyst tested. The activities for isobutene formation were CuV 2O 6 > ZnV 2O 6, NiV 2O 6, CoV 2O 6 > MgV 2O 6 > MnV 2O 6 ≫ CaV 2O 6. Isobutene was a major product over M 2V 2O 7 (MM). Co 2V 2O 7 showed the highest activity and high isobutene selectivity exceeded 90%, demonstrating that Co 2V 2O 7 is a suitable oxide for a thin layer reactor for anaerobic oxidation of isobutane. Partial substitution of Mg by Cu in Mg 2V 2O 7 (MM) improved the activity. It is shown by the oxidation at low O 2 concentration as 2–3% that two types of oxidations occurred simultaneously: isobutene formation by the lattice oxygen ions diffused from the bulk, and CO and CO 2 formation by the oxygen species derived from molecular oxygen in the gas phase.

Synthesis and characterization of MoVTeCeO catalysts and their catalytic performance for selective oxidation of isobutane and isobutylene

A series of Mo-based catalysts (MoVCeO, MoTeCeO, MoVTeO, and MoVTeCeO mixed metal oxides) were prepared and tested for the oxidation of isobutane and isobutylene. Characterization results (XRD, FTIR, TPR, XPS, and BET) showed that their structure and properties depend on the composition of the calcined samples. Catalytic tests showed that molybdenum may be the key element for the activation of isobutane, whereas the selective oxidation of isobutylene to methacrolein (MAL) might proceed mainly on the surface of the TeMo-containing crystalline phase. In addition, Te4+ may favor the formation of methacrylic acid (MAA). The incorporation of Ce ions may modify the redox process of the catalysts and thus influence the catalytic behaviors for the selective oxidation of isobutane. Thus, the selectivities and yields of MAL and MAA can be increased over these specially designed catalysts.

The dispersion of Keggin-type P/Mo polyoxometalates inside silica gel, and the preparation of catalysts for the oxidation of isobutane to methacrolein and methacrylic acid

Abstract Keggin-type P/Mo polyoxometalates (POM) were dispersed in a high-surface-area silica gel by means of a co-gelation procedure, in order to prepare catalysts for the gas-phase oxidation of isobutane to methacrolein and methacrylic acid. The aim was the dilution of the active phase, in order to favor the dispersion of the considerable reaction heat and limit the oxidative degradation of the desired products. However, the diluted heteropolyacid was less stable than the undiluted one, because of the exchange between P and Si as the heteroatom. When the gel was prepared in the presence of tetrapropylammonium hydroxide, the thermal decomposition of the latter generated the ammonium ion that replaced for protons in the cationic position of the POM. This enhanced the structural stability of the diluted POM at 350 °C under reaction conditions. However, no improvement of the catalytic performance was obtained for the diluted catalysts as compared to the undiluted systems, because of the combustion of methacrylic acid, of the modification of the POM redox properties and of the considerable extent of POM decomposition.

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.

Structural evolution of H 4PVMo 11O 40⋅ xH 2O during calcination and isobutane oxidation: New insights into vanadium sites by a comprehensive in situ approach

H 4PVMo 11O 40⋅8H 2O was studied during thermal activation as well as during isobutane oxidation by simultaneous in situ-EPR/UV–vis/Raman spectroscopy, in situ-FTIR spectroscopy, and quasi-in situ- 1H and - 51V-MAS-NMR. In as-synthesized form, most V sites are pentavalent, octahedrally coordinated, and located within the intact Keggin anions. Stepwise dehydration in N 2 up to 350 °C leads to partial reduction and disintegration of the V sites from the Keggin units, followed by their condensation on the outer surface of the latter in square-pyramidal form. In water-free H 4PVMo 11O 40, only V 5+ (not V 4+) is stable inside the Keggin unit. Thus, disintegration of V from the latter is favored by its reduction to the tetravalent state and thus depends on the redox properties of the atmosphere. Active sites in isobutane oxidation are most likely composed of single O 4V 4+/5+ O species connected to Mo 6+ via oxygen bridges. Partial deactivation occurs by formation of carbon-containing deposits.