Selective heterogeneous hydrocarbon oxidation over oxide catalysts

The heterogeneously-catalysed oxidation of hydrocarbons over oxide catalysts is reviewed. The first section of the paper deals in a general way with the structural features of hydrocarbons and relates these to the selective oxidation products which may be obtained from them. The interaction of oxygen and hydrocarbons with oxides is also considered in a general context and the kinetics of heterogeneous oxidation of hydrocarbons are discussed. The second section of the paper deals in more detail with the selective oxidation of aromatic hydrocarbons with particular reference to vanadium oxide containing catalysts. Finally, an account is given of the selective oxidation of monoalkenes to 1,3 conjugated systems and ketones over mixed oxide catalysts. The information available is considered throughout with a view to revealing those features of such systems which give rise to the selectivity.     

Correlations between the optical basicity of catalysts and their selectivity in oxidation of alcohols, ammoxidation and combustion of hydrocarbons

The optical basicity Λ of metallic oxides is obtained by a linear combination of the optical basicity of cations and depends on their valence, coordination and spin state. Λ quantifies the electron donor/acceptor power of the solid, which may be correlated with its redox properties. During catalysis, it is expected that the electron donor/acceptor property of the selective catalyst matches the acceptor/donor property of the reactant to be selectively transformed into the product. The selectivity is accounted for by ΔI which is the difference between the ionization energies of reactant and product. Each selective catalyst/reactant–product couple is characterized by {Λ, ΔI} value. Linear relationships between the {ΔI, Λ} obtained for various catalyst/reaction couples are drawn for several types of selective oxidation reactions: mild oxidation of alkanes, of olefins and of alcohols, ammoxidation of hydrocarbons, total oxidation of alkanes and of olefins.     

Engineering Cytochrome P450 BM3 for Terminal Alkane Hydroxylation

Enzymes that catalyze the terminal hydroxylation of alkanes could be used to produce more valuable chemicals from hydrocarbons. Cytochrome P450 BM3 from Bacillus megaterium hydroxylates medium‐chain fatty acids at subterminal positions at high rates. To engineer BM3 for terminal alkane hydroxylation, we performed saturation mutagenesis at selected active‐site residues of a BM3 variant that hydroxylates alkanes. Recombination of beneficial mutations generated a library of BM3 mutants that hydroxylate linear alkanes with a wide range of regioselectivities. Mutant 77‐9H exhibits 52% selectivity for the terminal position of octane. This regioselectivity is octane‐specific and does not transfer to other substrates, including shorter and longer hydrocarbons or fatty acids. These results show that BM3 can be readily molded for regioselective oxidation.     

Solubility of light alkanes and alkenes in ionic liquids

The solubility of light hydrocarbons in a variety of ionic liquids was studied, and it was found that ionic liquids containing Cu(Ⅰ) had higher solubility for hydrocarbons and alkene/alkane solubility selectivity, and Et₃NHCl-2.1CuCl ionic liquid was preferred. The effects of temperature and pressure on the solubility of light hydrocarbons were investigated for the selected ionic liquid. It was found that low temperature and high pressure were favorable for the dissolution of light hydrocarbons, and the alkene/alkane solubility selectivity decreased with the increase of temperature and pressure. The alkene/alkane solubility selectivity was above 8.3 at the temperature of 30℃ and the pressure of 0.2 MPa. The initial dissolution rate of hydrocarbons in ionic liquid was large, but it decreased rapidly with prolonging time, and the dissolution rate of alkenes was higher than that of alkanes at the same conditions. The alkene/alkane separation selectivity increased with decreasing content of alkenes in the mixture of alkenes and alkanes. Light hydrocarbons dissolved in ionic liquids could be desorbed by means of increasing temperature, restoring the dissolution capability of ionic liquids to hydrocarbons. Alkanes were easier to be desorbed than alkenes, and small-molecule hydrocarbons were easier to be desorbed than large-molecule hydrocarbons. The desorption percentage exceeded 92% under optimal conditions. Ionic liquid had a good reusable performance in the absorption and separation of light alkanes and alkenes. The solubility only decreased by less than 5% when it was reused five times, and the alkane/alkane solubility selectivity was basically not affected by reusing times. Software Gaussian 09 was used to study the interaction between anions of ionic liquids and light alkanes and alkanes, and the solubility difference of light alkenes and alkanes in different ionic liquids was well explained.     

Efficient aerobic oxidation of hydrocarbons with O2 catalyzed by DDQ/NHPI

BACKGROUND: Organocatalysis, a promising strategy for the oxidation of organic compounds, does not involve the use of a catalytic metal. In this work, an efficient organocatalyst system consisting of 2,3‐dichloro‐5,6‐dicyano‐benzoquinone (DDQ) and N‐hydroxyphthalimide (NHPI) was studied. RESULTS: 72.2% conversion with 92.3% selectivity for acetophenone was obtained in ethylbenzene oxygenation catalyzed by DDQ/NHPI under 0.3 MPa of molecular oxygen at 80 °C for 10 h. In addition, other hydrocarbons were also oxidized with high efficiency using this catalyst system. UV/Vis spectroscopy of the catalytic system indicated that DDQ accelerated the generation of free radical phthalimido‐N‐oxyl (PINO) by abstracting a hydrogen atom from NHPI. CONCLUSION: An efficient organocatalyst system consisting of DDQ and NHPI for selective oxidation of hydrocarbons to corresponding ketones with molecular oxygen as oxidant is reported. DDQ promoted the generation of PINO from NHPI, and the oxidation reaction was accelerated via PINO. This organocatalyst system should be useful for the design of highly selective catalysts for hydrocarbon oxidation. Copyright © 2010 Society of Chemical Industry     

小分子烷烃与烯烃在离子液体中的溶解性能

研究了多种离子液体对小分子烃类的溶解性能,发现含有Cu(Ⅰ)的离子液体对烃类具有较高的溶解度和烯烃/烷烃溶解选择性,优选出了Et₃NHCl-2.1CuCl离子液体。考察了温度和压力对小分子烃类溶解性能的影响规律,发现低温和高压有利烃类的溶解,烯烃/烷烃溶解选择性随温度和压力的升高而减小;在30℃和0.2 MPa的条件下,烯烃/烷烃溶解选择性均在8.3以上。烃类在离子液体中的初始溶解速率较大,但随时间的延长快速降低,相同条件下烯烃的溶解速率高于烷烃的溶解速率。烯烃/烷烃分离选择性随混合气中烯烃含量的减小而增大。升温可以解吸出离子液体中的烃类,烷烃比烯烃容易解吸,优化条件下的解吸率可达92%以上。离子液体对小分子烷烃和烯烃的吸收分离具有良好的重复使用性能。利用Gaussian 09软件对离子液体的阴离子与烯烃、烷烃的作用进行了计算分析,解释了烯烃和烷烃在不同离子液体中溶解性能差异的原因。     

低碳烷烃选择性氧化高分散活性位催化剂的研究进展

石油资源的过渡消耗导致化工原料短缺危机,低碳烷烃选择性氧化可以有效缓解危机并降低化工原料成本。高分散活性位催化剂在低碳烷烃选择性氧化反应中具有特殊催化作用和广阔的应用前景,在石油化工行业发展中具有巨大的潜能。基于国内外研究者在高分散活性位催化剂用于低碳烷烃选择性氧化领域的研究工作,介绍高分散活性位催化剂的制备方法,总结低碳烷烃选择性氧化高分散活性位催化剂体系,分析低碳烷烃选择性氧化反应机理。重点评述钒基、钼基和铁基高分散活性位催化剂用于低碳烷烃选择性氧化反应的催化性能及反应机理。并对高分散活性位催化剂在低碳烷烃选择性氧化中存在的问题、发展趋势和应用前景进行总结和展望。     

Metal‐Free: An Efficient and Selective Catalytic Aerobic Oxidation of Hydrocarbons with Oxime and N‐Hydroxyphthalimide

A non‐metal catalytic system consisting of dimethylglyoxime (DMG) and N‐hydroxyphthalimide (NHPI) for the selective oxidation of hydrocarbons with dioxygen is described. The synergistic effect of DMG and NHPI ensures its efficient catalytic ability: 82.1% conversion of ethylbenzene with 94.9% selectivity for acetophenone could be obtained at 80 °C under 0.3 MPa of dioxygen in 10 h. Several hydrocarbons were efficiently oxidized to their corresponding oxygenated products under mild conditions.     

Struktur-Aktivitäts/Selektivitäts-Beziehungen von Oxidationskatalysatoren

Structure-Activity/Selectivity Correlation of Oxidation Catalysts Various reactive forms of oxygen are active in the selective oxygen functionalization of olefins and aromatic compounds. These forms are different on different crystal faces of transition metal oxides as shown by their different cation-oxygen bond lengths. Therefore, face specifity of transition metal oxides as catalysts can be expected for the selective oxidation of hydrocarbons. Furthermore, the reactivity of the framework oxygen in the transition metal oxides for selective oxygen functionalization of hydrocarbons is dependent on the nature of the catalytic cycle (one- or two-electron-processes). Therefore, structure sensitivity of oxidation catalysts on the selectivity of transition metal oxides as oxidation catalysts is possible. Starting from this concept the following phenomena of the activity/selectivity relations are discussed for the most important industrial oxidation catalysts:

• —ensemble effects on the selectivity of supported Ag catalysts for the oxidation of ethylene to ethylenoxide.
• —face specifity of multicomponent Bi/Mo-oxide catalysts in the selective oxidation of propylene to acrolein and in the ammoxidation of propylene.
• —structure sensitivity of V₂O₅-containing catalysts in the oxidation of aromatic compounds.

     

烃类晶格氧选择性氧化催化剂研究进展

用晶格氧代替气相氧,是烃类选择性氧化一种新工艺,该工艺可以避免烃类的深度氧化,提高选择性,不受爆炸极限的限制,可以提高生产能力,降低成本。本文介绍了晶格氧氧化的反应机理,综述了不同烃类选择性氧化中的晶格氧催化剂的制备及应用现状,提出未来烃类选择性氧化的晶格氧催化剂的主要发展方向。     

Selective Oxidation of Organic Substrates in Presence of H2O2 using a Polymer-Anchored Iron(III)-Ferrocene Complex

An eco-friendly, cheap and reusable polymer-anchored iron(III)-ferrocene Schiff base catalyst has been designed for the efficient oxidation of alkanes and alcohols. Oxidation reactions were done by using a greener oxidant 30 % aqueous hydrogen peroxide in acetonitrile medium at room temperature for alcohols and at 60 °C for alkanes. Both the alkanes and alcohols have been selectively oxidized to their corresponding aldehydes and ketones in excellent yields. This catalyst has shown excellent catalytic activity with high selectivity and recyclability. It is found that this catalyst can be reused up to six cycles without loss of its original activities.     

Ultrasound-assisted co-precipitation synthesis of mesoporous Co3O4–CeO2 composite oxides for highly selective catalytic oxidation of cyclohexane

The one-step highly selective oxidation of cyclohexane into cyclohexanone and cyclohexanol as the essential intermediates of nylon-6 and nylon-66 is considerably challenging. Therefore, an efficient and low-cost catalyst must be urgently developed to improve the efficiency of this process. In this study, a Co₃O₄–CeO₂ composite oxide catalyst was successfully prepared through ultrasound-assisted co-precipitation. This catalyst exhibited a higher selectivity to KA-oil, which was benefited from the synergistic effects between Co³⁺/Co²⁺ and Ce⁴⁺/Ce³⁺ redox pairs, than bulk CeO₂ and/or Co₃O₄. Under the optimum reaction conditions, 89.6% selectivity to KA-oil with a cyclohexane conversion of 5.8% was achieved over Co₃O₄–CeO₂. Its catalytic performance remained unchanged after five runs. Using the synergistic effects between the redox pairs of different transition metals, this study provides a feasible strategy to design high-performance catalysts for the selective oxidation of alkanes.     

Unterschiede in der Totaloxidation organischer Verbindungen an heterogenen Platin- und Palladiumkatalysatoren

Differences in the Total Oxidation of Organic Compounds on Heterogeneous Pt- and Pd-Catalysts The catalytic oxidation of selected organic compounds was studied on supported Pd and Pt catalysts and on massive wires. Unfunctionalized (Decane), unsaturated (dodecene, benzene), oxygen containing (1-octanol, formaldehyde, acetone, n-butylacetate, formic acid), nitrogen containing (aniline, pyridine), sulfur containing (thiophene) and chlorinated (1,2-dichloroethane) hydrocarbons were used as model compounds. The relative activity of the metals for oxidation of the various compounds was determined from the turnover frequencies. While platinum is more active for the oxidation of the unfunctionalized, aromatic and chlorinated compounds, palladium is more active for nitrogen and sulfur containing compounds and for formic acid. No specificity is found for alkenes and compounds with a lower oxygen content. In the presence of octane, the unreactive pyridine is much more effectively oxidized than pyridine alone. There are distinct differences for the oxidation of octane/pyridine mixtures on bimetallic, mixed and pure Pt- and Pd-catalysts. The bimetallic catalyst and the pure Pt-catalyst dominate with respect to conversion and selectivity. The oxidation of linear alkanes on Pt correlates with the boiling point. Pd catalyzes the oxidation of lower hydrocarbons (< C₅) better, while higher hydrocarbons ( > C₅) are better oxidized by Pt.     

Present State of Ideas on the Mechanism of Catalytic Hydrocarbon Oxidation

A large amount of research has recently been devoted to oxidative conversions of hydrocarbons, and many laboratories in various countries are concerned with this problem. This field of catalysis has been extensively studied. The new, particularly spectroscopic, experimental methods provide additional information on the structures of surface compounds formed by interactions of various reactants with the catalyst. The very sensitive chromatographic technique has made possible the detection of multiple oxygen compounds yielded by oxidation of hydrocarbons of various structure so that the possibility of various conversion paths has become evident. Many schemes for the catalytic oxidation of hydrocarbons, particularly of olefins and aromatics, have been proposed. Considerably less extensive was the research on the oxidation of alkanes.     

Electronic Effect of Substituent of Quinones on their Catalytic Performance in Hydrocarbons Oxidation

Quinones with electron-withdrawing F, Cl or Br groups and N-hydroxyphthalimide (NHPI) were used as catalysts in selective oxidation of hydrocarbons with molecular oxygen as oxidant. The catalytic activity in the selective oxidation of ethylbenzene to oxygenation products was in the following order: p-benzoquinone < tetrafluoro-p-benzoquinone ≈ tetrachloro-p-benzoquinone < tetrabromo-p-benzoquinone (p-TBBQ). Moderate electron-withdrawing power of substituent was suitable for quinone abstracting hydrogen from NHPI to generate reactive phthalimido-N-oxyl (PINO). The catalytic activity of p-TBBQ/NHPI, the best catalyst in our study, was also tested in the selective oxidation of alkylarenes, alkenes and alkanes.     

Recent Advances and Future Aspects in the Selective Isomerization of High n‐Alkanes

This article provides an overview of the advances that have been marked during the last decades in the field of hydroconversion of high n‐alkanes (C₇ ⁺) with particular stress on the promising ways to meet the requirements for improved quality of motor fuels and oils. Particular attention is given to a catalyst formulation for selective conversion of high n‐alkanes to branched hydrocarbons. The challenge for successfully solving this problem is to find an effective catalyst favoring the isomerization of n‐alkanes without too much cracking. The regulation of active sites and adsorption properties, as well as the topology of support surfaces, allows a more predictive design of novel catalysts for selective conversion of high n‐alkanes into their branched isomers.     

Selective oxidation of hydrocarbons under air using recoverable silver ferrite–graphene (AgFeO2–G) nanocomposite: A good catalyst for green chemistry

The selective oxidation of hydrocarbons is a main academic and industrial research challenge. A lot of researches have been done about this issue, but till now relatively little attention has been paid to graphene-complex oxide nanocomposites. Herein, we report our studies on a new catalyst. Silver ferrite–graphene (AgFeO₂–G) as a separable nanocomposite from the reaction solution, was used as an effective oxidizing agent for the oxidation of various hydrocarbons (1- decene, cyclohexene, cis-cycloctene, cyclohexane, cyclooctane etc.) under mild conditions (55 ^০C, 8 h) with high conversion and selectivity using air, that is proper for ‘green’ chemistry. Metal or metal oxide nanoparticles assembled on graphene sheets revealed high electrocatalytic activity. Indeed, AgFeO₂ with graphene due to low band gap and graphene oxide with large amounts of oxygen-containing groups, provide facility catalytic activity of catalyst-supported system. We also found that, with this catalyst, selective oxidation could be achieved without the need for the addition of solvent, which is appropriate in particular for ‘green’ chemistry. The catalysts showed little deactivation and maintained their conversion and selectivity levels duration of the measurements.     

Bridging Heterogeneous Catalysis and Electro-catalysis: Catalytic Reactions Involving Oxygen

Catalytic reactions that involve oxygen can be found in a large number of processes, including those in energy-related applications, in emission control and in processes important for the chemical industry. Whether the catalytic step is an oxygen insertion step as in a selective oxidation reaction, or an oxygen removal step as in a hydrodeoxygenation reaction, oxygen has proven to be a very challenging component, often determining the selectivity of the reaction. Some examples from our laboratories that bridge catalysis and electro-catalysis will be discussed, ranging from oxidative dehydrogenation of alkanes to oxygen reduction reaction in fuel cells.     

Modification of the surface reactivity and selectivity of mixed oxides in oxidation reactions due to coadsorbate species

The influence of coadsorbate species on the surface properties of mixed oxides in the selective oxidation of hydrocarbons is shown to highlight the concept of the possibility to tune the reactivity and selectivity with gas phase dopants and the role of coadsorbate species in the reaction mechanism of selective oxidation. Although few literature data are available on these topics, the examples discussed illustrate that a better understanding of these phenomena is a key to the design of better catalysts and a critical factor in understanding the real nature of the surface processes during the catalytic reaction.     

丙烷直接氧化制丙烯酸的研究进展及展望

丙烷直接氧化制丙烯酸是近年来烃类催化氧化的热点课题。MoVTeNbOx复合金属氧化物催化剂被认为是目前对于该反应催化性能最好的一类催化剂。作者针对在丙烷直接氧化制丙烯酸领域中影响MoVTeNbOx系列金属氧化物催化性能的因素及将来可能开发的烃类选择氧化反应新工艺两方面进行综述。