Catalytic Oxidation Of Olefins Research Articles

Catalytic partial oxidation of alkanes on silver in fluidized bed and monolith reactors

We have examined catalytic oxidation of alkanes on supported Ag catalysts at high temperatures (>800°C) in both fluidized bed and monolithic reactors at contact times of 50–200 and 5–10 ms, respectively. The results obtained on Ag are compared with Pt for both fluidized beds and monoliths. Oxidation of CH 4, C 2H 6, and i-C 4H 10 are examined on 0.25–0.5 wt.% Ag α-Al 2O 3 in fluidized beds while CH 4 and C 2H 6 oxidations and ammoxidations are examined on 4–35 wt.% Ag monoliths supported on α-Al 2O 3. We find that alkanes do not dissociate as easily on Ag as on Pt, and in both types of reactors it is not possible to keep CH 4 ignited on Ag at any feed composition without the presence of NH 3 which is used for light-off. C 2H 6 and i-C 4H 10 are much more reactive than CH 4, and in fluidized beds, we observe high selectivities to olefins (60–75%) at 80 to 90% conversion with no problems of extinction. Also, there is no carbon buildup or evidence of any Ag loss from the catalyst at the high temperatures (ca. 800°C) over at least 16 h of operation. On the Ag monoliths under ammoxidation conditions (alkane + NH 3 + O 2) used for HCN synthesis on Pt monoliths and gauzes, <0.005% HCN is produced from both CH 4 and C 2H 6. For C 2H 6 oxidation, external heat input is necessary to keep the monoliths ignited with C 2H 4 being the dominant product (64% selectivity). Although the performance of Ag is very close to that of Pt, it is difficult to keep C 2H 6 ignited which extinguishes quickly below 800°C. At very high temperatures (>1100°C), metal losses are observed for Ag monoliths. We also examined Au and PtAu monoliths for C 2H 6 oxidation. Although the monoliths can be ignited using NH 3 and O 2, they extinguish as soon as C 2H 6 is introduced. Reactions on Ag appear to be initiated by oxidative H-abstraction from the alkane by a strongly bound oxygen species on the surface to form a surface alkyl. β-H or β-alkyl elimination reactions of the adsorbed alkyl then dominate just as on Pt leading to olefins rather than cracking to C s and H s.

ALKANE PARTIAL OXIDATION

Direct partial catalytic oxidation of alkanes to commercial chemicals has received a boost from a microsecond reactor under development at the University of Minnesota, Minneapolis. The reactor can convert n -butane to formaldehyde and olefins in high yield, with high selectivity [ Science , 271, 1560 (1996)]. Developed by professor of chemical engineering Lanny D. Schmidt and graduate student Duane A. Goetsch, the reactor employs a 90% platinum- 10% rhodium gauze catalyst inside a quartz tube less than 2 cm in diameter. The room-temperature alkane gas heats rapidly to 800 °C as it flows past the gauze. The product gases are then rapidly thermally quenched before they can be totally oxidized to carbon dioxide and water. Catalytic partial oxidation of light alkanes, particularly those in natural gas, has always attracted commercial interest. The problem has been to control nonselective reactions that produce mostly carbon oxides. The microsecond reactor provides the necessary kinetic controls to stop the re...

Olefins by Catalytic Oxidation of Alkanes in Fluidized-Bed Reactors

The production of ethylene or syngas from ethane and olefins from propane, n-butane, and isobutane in the presence of air or O2 at atmospheric pressure has been examined over 100 μm α-Al2O3 beads coated with noble metals in a static fluidized bed reactor at contact times from 0.05 to 0.2 s. Variations in feed composition, preheating temperature, and flow rate were examined. For ethane on Pt, we observe selectivities to ethylene in excess of 72%, with conversions above 85% at the oxidative dehydrogenation stoichiometry (alkane/O2 = 2.0) for a 62% single-pass yield which is 5% higher than previously observed on Pt monoliths. On Rh, CO, and H2 (syngas) production dominates with CO and H2 selectivities up to 90% at nearly 100% ethane conversion. With propane and n-butane on Pt, we observe 55-60% and 65-70% selectivity to olefins, respectively, with >90% conversion for both alkanes. Ethylene and propylene are the major olefin products for both alkanes. Ethylene production dominates at higher temperatures and longer contact times while propylene production is favored at lower temperatures and shorter contact times. With isobutane on Pt, we observe 60-70% olefins with 80% conversion with isobutylene and propylene as the dominant olefins. For all alkanes, C2H2 formation was ≤ 0.8% and C4H6 and aromatics were less than 0.05%. Although all experiments were carried out in a regime predicted to be severely coke forming, no carbon buildup was observed on any of the catalysts and the catalysts exhibit no evidence of deactivation over several days. A simple reaction mechanism appears to explain the observed product distributions. Reactions are initiated by oxidative dehydrogenation of the alkane by adsorbed oxygen to form a surface alkyl. On Pt, β-hydrogen and β-alkyl elimination reactions of adsorbed alkyl dominate, which lead to olefins rather than cracking to Cs and Hs. On Rh, Ni, and Pd β-hydrogen elimination is not preferred and cracking to Cs and Hs ultimately leads to syngas production (Rh, Ni) or carbon deposition (Pd).

ChemInform Abstract: Studies on the Catalytic Oxidation of Alkanes and Alkenes by Titanium Silicates.

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Studies on the Catalytic-Oxidation of Alkanes and Alkenes by Titanium Silicates

Titanium containing, aluminum-free ZSM-5 (TS-1) and amorphous TiO_2-SiO_2 coprecipitate are investigated as catalysts for the selective oxidation of alkanes and alkenes using a variety of oxidants at temperatures below 100°C. Comparisons between the activities of TS-1 and the TiO2-SiO2 coprecipitate for alkane oxidation and alkene epoxidation using nonaqueous H_2O_2 indicate that the absence of water is crucial for the catalytic activity of silica-supported titanium. Due to the hydrophobicity of TS-1, the concentration of water surrounding the titanium is maintained at a low value, and thus TS-1 can be used as an oxidation catalyst with aqueous H_2O_2 as oxidant. Alkyl hydroperoxides are active as oxidants for alkene epoxidation on the TiO_2-SiO_2 coprecipitate but not for alkane oxidation reactions on both TS-1 and the TiO_2-SiO_2 coprecipitate. A plausible explanation for the above results is provided. The presence of stereoscrambling without any radical clock rearrangement during alkane oxidation on TS-1 indicates that the radicals formed may have a very short life-time, or their movements are restricted such that no rearrangement can occur. A proposal for the mechanism of alkane oxidation on TS-1 is given and compared to a mechanism suggested for alkene epoxidation on TS-1 and the TiO_2-SiO_2 coprecipitate.

Azide activation of metallophthalocyanine complexes for the catalytic oxidation of alkanes in the liquid phase

Earlier work in our laboratories has shown that light alkanes can be air-oxidized using metalloporphyrin azides as catalysts. Phthalocyanine complexes are known to be more robust materials and cobalt phthalocyanine catalysts are used for mercaptan oxidations in the petroleum industry. Phthalocyanine complexes, however, are not very hydrocarbon soluble nor very active for low-temperature alkane oxidation. We report that chromium and manganese phthalocyanine azides catalyze selective oxidation of isobutane to tert-butyl alcohol and that iron perfluorophthalocyanine azides are robust, soluble, active catalysts for the selective oxidation of isobutane and propane under mild conditions of temperature and pressure.

Oxidation of alkanes with hydrogen peroxide catalysed by iron salts or iron oxide colloids in reverse microemulsions

Catalytic oxidation of alkanes occurs in reverse (water in oil) microemulsions stabilized by an anionic surfactant (Aerosol OT®). The catalytically active microemulsion is generated by mixing two reverse microemulsions containing respectively an aqueous solution of iron (Fe II or Fe III) and an aqueous solution of H 2O 2 (30%) dispersed in liquid alkanes (continuous oil phase). This microemulsion system is active in the CH bond oxidation of various liquid alkanes (cycloalkanes, decalin, tetralin, alkylbenzenes) into ketones and secondary and tertiary alcohols at room temperature. The selective oxidation of secondary carbons into ketones and tertiary carbons into alcohols is interpreted by the intervention of iron(V) oxene intermediates rather than radical Fenton-type mechanisms. Polynuclear aggregates such as colloidal hydrous ferric oxides generated by hydrolysis within the aqueous microdroplets are assumed to be the catalytically active species. In fact, we demonstrate that previously prepared iron oxide colloids (Fe 2O 3 and FeOOH) similarly catalyze the oxidation of alkanes with hydrogen peroxide in reverse microemulsions. The low interfacial water—hydrocarbon tension and the very high interfacial area in liquid—liquid dispersions greatly favour the catalytic process.

Functionalization of silica gel: application for the catalytic oxidation of alkanes

Silica gel, functionalized by (N,N-dimethyl-3-aminopropyl) trimethoxysilane and complexed with Fe-(II) or other metal ions in the presence of O 2 was effective for the aerobic, room temperature oxidation of a C-H bond in cyclohexane. The products were cyclohexanol and cyclohexanone

Syntheses, electrochemistry and reactivities of pyridine amide complexes of chromium(III) and manganese(III)

Reactions of anhydrous CrCl3 with H2bpb and H2bpc [H2bpb = 1,2-bis(pyridine-2-carboxamido)benzene; H2bpc = 4,5-dichloro-1,2-bis(pyridine-2-carboxamido)benzene] in dimethylformamide and manganese(III) acetate with H2bpc in methanol, yielded the respective [CrIII(bpb)Cl]·xH2O, [CrIII(bpc)Cl]·H2O and [MnIII(bpc)(O2CMe)] complexes. The electrochemistry of the chromium(III) amide complexes has been studied by cyclic voltammetry. They exhibit reversible oxidation couples with E° values ranging from 0.28 to 0.80 V vs. ferrocenium–ferrocene. Except for [CrIII(bpb)(CN)2]– which has a quasireversible reduction couple at –1.97 V, the electrochemical reductions are irreversible. The complexes [CrIII(bpb)(H2O)2]ClO4, [CrIII(bpb)Cl(MeOH)] and [MnIII(bpc)(O2CMe)] have been shown to catalyse olefin epoxidation by iodosobenzene. With [Mn(bpc)(O2CMe)], catalytic oxidation of alkanes by PhIO has also been observed. An oxygen-rebound mechanism involving a MnvO or a CrvO intermediate is proposed for the PhIO oxidation reactions.

On the molecular mechanism of catalytic oxidation of olefins

In every oxidation reaction two reactants take part: oxygen and the molecule to be oxidized. The reaction may thus start either by activation of the dioxygen (electrophilic oxidation) or by activation of the hydrocarbon molecule (nucleophilic oxidation). The surface of an oxide catalyst for selective oxidation must thus be tailored to perform a complex multistep operation on the reacting molecules, at the same time hindering those interactions that could lead to unwanted byproducts.

Manganese complexes of 1,2-naphthoquinone mono-oximes (2-nitrosophenols) as catalysts for alkene epoxidation

Epoxides are the major products of the catalytic oxidation of alkenes (cyclohexene, styrene, oct-1-ene, and methyl oleate) with dioxygen using the complexes Mn(1-nqo)n as catalysts (n= 2 or 3, 1- and 2-nqoH = 1,2-naphthoquinone 1- and 2-oxime).

Electrochemical model of alkane oxidation by cytochrome P-450

Catalytic oxidation of alkanes to alcohols and ketones was shown to take place in an electrochemical cell with iron porphyrin deposited on a graphite cathode. The oxidation mechanism was assumed to be similar to that of cytochrome P-450 action.

Factors affecting selectivity and activity of oxidation catalysts

Robert K. Grasselli Chemistry Department, Case Western Reserve University Cleveland, Ohio 44106, U.S.A. Received May 15, 1987 Selective catalytic oxidation of olefins has been successfully practiced on a commercial scale for almost thirty years {1). Processes which have been commercialized are the oxydehydrogenation of n-butenes to butadiene (a two electron oxidation), the oxidation of propylene to acrolein (a four electron oxidation) and its subsequent oxidation to acrylic acid (a two electron oxidation), and the ammoxidation of propylene to acrylonitrile (a six electron oxidation) (2). More recently the fourteen electron oxidation of n-butane to maleic anhydride has been achieved catalytically and will be commercialized in the near future (3). Fundamental studies pertaining to these processes have shed a considerable light on the mechanistic intricacies of catalysts effective in selective oxidation (4).

Peroxo and alkylperoxidic molybdenum(VI) complexes as intermediates in the epoxidation of olefins by alkyl hydroperoxides

Novel oxoperoxomolybdenum(VI) complexes with the general formula MoO(O 2)L 2X 2 (III, L = DMF, HMPT) and MoO(O 2)Cl(ON)L(IV, ON) = pyridin-2-carboxylate (Pic), 8-hydroxyquinolinate (Quin) were prepared from the reaction of Ph 3COOH or H 2O 2 with the corresponding cis-dioxo complexes. In the reaction with Ph 3COOH both oxygen atoms of the peroxo moiety were found, by 18O labeling experiments, to come from the hydroperoxide. The X-ray crystal structure of MoO(O 2)Cl(Pic)(HMPT) revealed a bipyramidal pentagonal surounding with a rather short OO distance (1.41 Å). Complexes III were found to be more reactive than MoO(O 2) 2,HMPT for the epoxidation of olefins (oxidative cleavage products are consecutively formed) but react by the same cyclic peroxymetalation mechanism. The absence of reaction in the case of complexes IV illustrates the necessity for the metal to possess an equatorial releasable coordination site adjacent to the peroxo group for the oxygen transfer to occur. Catalytic oxidation of olefins using Ph 3COOH gave a selectivity in oxygenated products very different from that using t-BuOOH, and 18O labeling studies showed that alkyl-peroxidic rather than peroxo species are intermediates in this latter reaction. The mechanism of epoxidation of olefins by alkyl hydroperoxides catalyzed by d 0 metal complexes is discussed.

Epoxidation of cyclic alkenes by bis(acetonitrile)chloronitropalladium(II): on the role of heterometallacyclopentanes and .beta.-hydrogen elimination in the catalytic oxidation of alkenes

Reaction of the palladium complex with norbornene in acetone leads to the quantitative formation of the metallacycle, which can be isolated as a yellow solid. Decomposition of this metallatricycle under nitrogen in toluene solution produces exo-epoxynorbornene (ca 90% yield) at an initial rate of 3%/h. Part of this stability and change in product selectivity is attributed to the allycyclic bridgeheads. Intrametallacyclic ..beta..-hydrogen is restricted by the rotational rigidity of the bicyclic norbornane skeleton and by the attendant reintroduction of ring strain. 1 table.

Antimony-121 Mössbauer investigations of tin–antimony oxides

Catalytically active tin–antimony oxides have been investigated by 121Sb Mossbauer spectroscopy. Materials prepared by coprecipitation and dehydrated at 600 °C for 16 h give single-phased blue solids containing both SbIII and SbV in oxygen environments. Materials containing more than 20% antimony and heated for longer periods or at higher temperatures give the segregation of an additional antimony oxide phase. Samples with an antimony concentration of less than ca. 10% contain SbV within the tin(IV) oxide rutile lattice. Although the Mossbauer spectra provide evidence for an increase in s-electron density at both tin and antimony nuclei, the data give no indication of any reduction processes leading to the formation of either SnII or SbIII. A mechanism for charge compensation is proposed which involves the delocalization of electrons into a conduction band. The reaction of the tin–antimony oxides with hydrogen and the use of the material in the catalytic oxidation of olefins is accompanied by the reduction of SbV to SbIII.

Catalytic oxidation of olefins over oxide catalysts containing molybdenum: VI. Kinetics of propylene oxidation to form acetone over SnO 2MoO 3

The reaction mechanism of propylene oxidation to acetone over SnO 2MoO 3 catalyst has been investigated in terms of the kinetics at 130 °C. Isopropyl alcohol (IPA) showed the behavior of an intermediate product. The selectivity to IPA approached 100% in the very beginning of the oxidation. Thus it was confirmed that acetone formation proceeds first through hydration to IPA, followed by oxidative dehydrogenation. The kinetics of the propylene oxidation disclosed a significant retardation by ketone. Comparison of the rates for hydration of propylene, dehydration of IPA, and oxidative dehydrogenation of IPA suggested that there is no single rate-determining step in the formation of acetone from propylene.

Etude par spectroscopie de photoelectrons des interactions metal—support dans des catalyseurs a l'iridium depose sur des oxydes metalliques

Several iridium supported catalyst were studied by means of x-ray photoelectron spectroscopy. These catalysts contain 5 wt. % iridium impregnated from aqueous solution of hexachloroiridic acid on δ-alumina, silica, zinc oxide, titanium oxide and Ketjen silica alumina and are used in catalytic oxidation of olefins. Photoelectron spectra of oxides, impregnated oxides and hydrogen reduced catalysts have been recorded. Chemical shifts observed on impregnated oxides indicate that alumina and titanium oxide make possible the reduction of some of the hexachloroiridates ions into an iridium(III) chloro complex. This reaction is not detected with zinc oxide and silica. For the reduced catalysts, the iridium 4f doublet is shifted to higher binding energies with respect to that of unsupported iridium and the iridium lines have an anomalous breadth. We have postulated that an electronic interaction occurs between the support acting as an electron acceptor and the metal acting as an electron donor. The chemical shifts depend on the nature of the support, increasing ZnO < SiO2 < TiO2 < Al2O3, and may be correlated with the Fermi level in the metallic oxide. With silica-alumina and progressively de-aluminated silica-alumina, a simultaneous variation of the iridium chemical shift and catalytic activity is observed.

Reaction Scheme of Acetic Acid Formation by Catalytic Oxidation of Olefins over V-Sn-W Oxide Catalyst

Oxidation of olefins and the possible reaction intermediates over V-Sn-W oxide catalyst have been studied in order to elucidate the reaction scheme of acetic acid formation from olefins.The main products from dthylene, propylene, butene, isobutene and butadiene are those which ate anticipated from apparent scission of double bonds of the elefins; acetic acid is obtained in good Yiald from propylene and butenes while the main products from ethylene and butadiene are carbon 30xides. Addition of steam in the oxidation of 1-butene increases the conversion of butenes and selectivity to acetic acid although it retards allylic oxidation and decomposition of acetic acid. Acetaldehyde is usually found in the oxidation of propylene, and butenes, and is not detected in the xidationof acetone and ethylmeylketon, e which are formed from isopropylalcohol and sr-bqtylalcohol, the possible intermediate, by oxidative dehydrogenation.These results suggest that acetic acid is neither formed via dxidative scissien of the double bond nor oxidative hydration through alcohol and ketone, but is mainly formed from acetaldehyde which in turn is produced through direct reaction of the active oxygen species with tfie Carbonium ion resulted from the olefin on acidic sites of the catalyst.

Interactions of oxygen with olefins adsorbed on zinc oxide

The interaction of oxygen with olefins adsorbed on ZnO was investigated by analysis of the reaction products in the gas phase. It was found that the oxygen uptake had occurred before the adsorbed olefin was oxidized to CO 2 and H 2O. This oxygen uptake was attributed to the formation of a surface olefin-oxygen complex. The reactivities for such complex formation increased in the order C 2H 4 < 1,3-C 4H 6 < C 3H 6 < 2-C 4H 8 < 1-C 5H 10. From these results it was concluded that the catalytic oxidation of olefins over ZnO proceeds via such surface complex formation.