Selective Oxidation Of Hydrocarbons Research Articles

Gold nanoparticles supported on three‐dimensional nitrogen‐doped graphene: an efficient catalyst for selective aerobic oxidation of hydrocarbons under mild conditions

The development of efficient and selective aerobic oxidation of alkylarenes to form more functional compounds by heterogeneously catalysed routes still presents a great challenge in the fine chemical industry and is a major research topic. In this work, gold nanoparticles supported on three‐dimensional nitrogen‐doped graphene‐based frameworks (Au NPs@3D‐(N)GFs) were successfully synthesized and found to have an impressive performance as bifunctional catalysts (nitrogen dopant as base and gold nanoparticles as active site) in the controlled oxidation of alkylarenes. The catalyst was found to be a simple bench top, stable, recyclable and selective catalytic system for the aerobic oxidation of various types of alkylarenes into their corresponding ketones at room temperature under environmentally friendly conditions with good yields and high selectivity. Copyright © 2015 John Wiley & Sons, Ltd.

Selective oxidation and oxidative dehydrogenation of hydrocarbons on bismuth vanadium molybdenum oxide

A systematic investigation of the oxidative dehydrogenation of propane to propene and 1- and 2-butene to 1,3-butadiene, and the selective oxidation of isobutene to methacrolein was carried out over Bi1−x/3V1−xMoxO4 (x=0–1) with the aim of defining the effects of catalyst and reactant composition on the reaction kinetics. This work has revealed that the reaction kinetics can differ significantly depending on the state of catalyst oxidation, which in turn depends on the catalyst composition and the reaction conditions. Under conditions where the catalyst is fully oxidized, the kinetics for the oxidation of propene to acrolein and isobutene to methacrolein, and the oxidative dehydrogenation of propane to propene, 1-butene and trans-2-butene to butadiene are very similar—first order in the partial pressure of the alkane or alkene and zero order in the partial pressure of oxygen. These observations, together with XANES and UV–Vis data, suggest that all these reactions proceed via a Mars van Krevelen mechanism involving oxygen atoms in the catalysts and that the rate-limiting step involves cleavage of the weakest CH bond in the reactant. Consistent with these findings, the apparent activation energy and pre-exponential factor for both oxidative dehydrogenation and selective oxidation correlate with the dissociation energy of the weakest CH bond in the reactant. As the reaction temperature is lowered, catalyst reoxidation can become rate-limiting, the transition to this regime depending on ease of catalyst reduction and effectiveness of the reacting hydrocarbons as a reducing agent. A third regime is observed for isobutene oxidation at lower temperatures, in which the catalyst is more severely reduced and oxidation now proceeds via reaction of molecular oxygen, rather than catalyst lattice oxygen, with the reactant.

C-H Bond Cleavage by Bioinspired Nonheme Oxoiron(IV) Complexes, Including Hydroxylation of n-Butane.

The development of efficient and selective hydrocarbon oxidation processes with low environmental impact remains a major challenge of the 21st century because of the strong and apolar nature of the C-H bond. Naturally occurring iron-containing metalloenzymes can, however, selectively functionalize strong C-H bonds on substrates under mild and environmentally benign conditions. The key oxidant in a number of these transformations is postulated to possess an S = 2 Fe(IV)═O unit in a nonheme ligand environment. This oxidant has been trapped and spectroscopically characterized and its reactivity toward C-H bonds demonstrated for several nonheme iron enzyme classes. In order to obtain insight into the structure-activity relationships of these reactive intermediates, over 60 synthetic nonheme Fe(IV)(O) complexes have been prepared in various laboratories and their reactivities investigated. This Forum Article summarizes the current status of efforts in the characterization of the C-H bond cleavage reactivity of synthetic Fe(IV)(O) complexes and provides a snapshot of the current understanding of factors that control this reactivity, such as the properties of the supporting ligands and the spin state of the iron center. In addition, new results on the oxidation of strong C-H bonds such as those of cyclohexane and n-butane by a putative S = 2 synthetic Fe(IV)(O) species that is generated in situ using dioxygen at ambient conditions are presented.

Efficient oxidation of hydrocarbons over nanocrystalline Ce1−xSmxO2 (x = 0–0.1) synthesized using supercritical water

Highly crystalline cubic Ce1−xSmxO2 (x = 0–0.1) is synthesized using supercritical water, which showed superior catalytic activity for selective oxidation of hydrocarbons.

ChemInform Abstract: Site Isolation and Phase Cooperation: Two Important Concepts in Selective Oxidation Catalysis: A Retrospective

AbstractReview: 101 refs.

A nickel-modified polyoxometalate towards a highly efficient catalyst for selective oxidation of hydrocarbons

A nickel-modified polyoxometalate compound was synthesized which exhibited excellent catalytic activity (conversion: 41.63%; selectivity: 97.21%) for selective oxidation of cyclooctene using air as an oxidant without a solvent.

Development of VPO catalysts supported on mesoporous modified material based on an aerosil gel

Supports modified with different organic substances and vanadium-phosphorus oxide catalysts on their basis were developed with the use of the barothermal treatment of aerosil. It was found that the anchoring of a modifier to the surface of a support occurred with the participation of OH groups. The modifier content found from differential thermal analysis data depended on the pore structure of the support and the nature of the modifier. It was demonstrated that, with the use of a modified support in the catalysts, a vanadyl hydrogen phosphate hemihydrate phase—the precursor of a catalyst for the selective oxidation of hydrocarbons—was formed; under reaction conditions, this precursor was converted into vanadyl pyrophosphate. On supporting, the phase grew from the micropore bulk and covered only part of the support surface. The synthesized catalysts exhibited high activity and selectivity in the reaction of n-butane oxidation under hydrocarbon-rich conditions and also in the oxidative dehydrogenation of ethane.

Selective oxidation of hydrocarbons on supported Au catalysts

The importance of proximity of isolated TiOx cluster to Au surface for the formation of acetone in the selective oxidation of propane was investigated using a model system of Au particles decorated with mononuclear TiOx units dispersed in silica clusters. The results showed that no acetone was formed without TiOx, and its formation was more prominent on a sample containing a higher density of TiOx. Covering a Au/TiO2 catalyst with a layer of TiOx-containing silica changed the product selectivity from predominently propene to acetone. The data strongly supported the importance of isolated TiOx clusters near the Au surface in acetone formation, and suggested the relevance of Au-TiOx interface sites. Such interface sites might also be important in selective propene epoxidation that was coupled to CO oxidation in a H2O-methanol mixture. Using oxygen isotope labeling technique, it was found that the proximal source of oxygen in propene oxide was not from H2O but from O2. The observation was consistent with a methyl hydroperoxide intermediate, which could be formed by oxidation of a Ti methoxy at the Au-support interface.

ChemInform Abstract: Nanoaggregates of Simple Mn Porphyrin Complexes as Catalysts for the Selective Oxidation of Hydrocarbons.

AbstractColloidal nanoparticles of a manganese porphyrin complex efficiently catalyze the oxidation of saturated hydrocarbons and the epoxidation of olefins.

Coordination chemistry of Co complexes containing tridentate SNS ligands and their application as catalysts for the oxidation of n-octane.

The selective oxidation of saturated hydrocarbons to terminal oxygenates under mild catalytic conditions has remained a centuries long challenge in chemical catalysis. In an attempt to address this challenge, two series of tridentate donor ligands {2,6-bis(RSCH2)pyridine and bis(RSCH2CH2)amine [R = alkyl, aryl]} and their respective cobalt complexes {Co[2,6-bis(RSCH2)pyridine]Cl2 and Co[bis(RSCH2CH2)amine]Cl2} were synthesized and characterized. Crystal structures of Co[2,6-bis(RSCH2)pyridine]Cl2 [R = -CH3 (), -CH2CH3 (), -CH2CH2CH2CH3 () and -C6H5 ()] are reported in which crystallized as a homo-bimetallic dimer that incorporated two bridging chloride atoms in an octahedral geometry around each cobalt center, while , and crystallized as mono-metallic species characterized by trigonal bipyramidal arrangement of ligands around each cobalt center. As catalysts for the homogeneous selective oxidation of n-octane, the catalysts yielded ketones as the dominant products with a selectivity of ca. 90% for the most active catalyst Co[bis(CH2CH2SCH2CH2)amine]Cl2 () at a total n-octane conversion of 23%. Using tert-butyl hydroperoxide (TBHP) as an oxidant, optimization of reaction conditions is also reported.

Selective oxidation of sulfides and hydrocarbons with H$_{2}$O$_{2}$ over manganese catalyst supported on nanoparticles

A new magnetically separable catalyst consisting of binuclear Mn(II) complex [Mn_2(HL)_2(H_2O)_4], HL = 2-[(2-hydroxy-benzylidene)-amino]-3-(4-hydroxyphenyl)-propionic acid, supported on (3-chloropropyl)-trimethoxysilane (CPTMS) functionalized silica-coated magnetic nanoparticles (MNPs) was prepared. The synthesized catalyst was characterized by several physico-chemical and spectroscopic methods. This immobilized complex was found to be an efficient heterogeneous catalyst for the oxidation of different sulfides and hydrocarbons using hydrogen peroxide (H_2O_2) as an oxidant. The catalyst is readily recovered by simple magnetic decantation and can be recycled several times with no considerable loss of catalytic activity.

Template-free fabrication of mesoporous carbons from carbon quantum dots and their catalytic application to the selective oxidation of hydrocarbons.

Mesoporous carbons (pore size 5 nm) were successfully synthesized without templates from carbon quantum dots. As catalysts, both mesoporous carbons and Cu nanoparticles on mesoporous carbons show superior catalytic activity and stability for the selective oxidation of cyclooctene.

Heterogeneous Catalyst for the Selective Oxidation of Unactivated Hydrocarbons Based on a Tethered Metal-Coordinated Cavitand

A new selective hydrocarbon oxidation heterogeneous catalyst has been developed by tethering an iron-coordinated cavitand to the surfaces of a SBA-15 mesoporous material. The resulting material was shown to catalyze the oxidation of cyclic hydrocarbons at room temperature and to be quite robust and easily recyclable. The role of the cavitand scaffold is to prevent the catalytic Fe ions from interacting directly with the silica surface and to provide a controlled environment for reversible redox catalysis. An induction period is required for the activation of the catalyst, during which a change in coordination of the iron ions to the tethered cavitand takes place.

Progress in Electronic and Vibrational Spectroscopy of Catalytic Materials and Catalytic Reactions: Theoretical and Experimental Studies

This special issue of Topics in Catalysis is based primarily on papers presented at the symposium on progress in spectroscopic studies relevant to catalysis held 19–23 August, 2012 at the 244th ACS National meeting in Philadelphia, Pennsylvania. The objective of the symposium was to bring together researchers in the fields of catalysis, surface science, and theory interested in various spectroscopies that can be used to study and understand catalytic materials and processes. The focus of the papers presented at the symposium was twofold. One focus concerned understanding the fundamental chemical and physical properties of the spectroscopies themselves and the other concerned the application of these spectroscopies to determine and elucidate catalytic reactions and processes. A key emphasis was for photoemission spectroscopies, including both core and valence level photoemission, and for vibrational spectroscopies, including both infrared and Raman. The successful design of catalytic materials requires an in depth, fundamental understanding of their physicochemical surface and bulk properties in addition to reaction kinetics and thermodynamic limitations. Among the processes of interest in this symposium were selective oxidation of hydrocarbons, CO/H2 conversion to C2 and C3 olefins and alcohols, hydrogen generation from renewable sources and CO2 conversion to hydrocarbons. For the correct interpretation of results obtained by the wide range of spectroscopic techniques used to study these materials, it is important to have theoretical guidance for the chemical and physical significance of the spectra. The papers presented at the symposium were in the following three broadly defined categories: (1) In-situ and Operando spectroscopy of catalytic materials and reactions, (2) Modeling of surfaces and surface reactions, and (3) electronic structure of surfaces and interfaces. This proceedings issue begins with the plenary paper presented by Dr. Somorjai on the catalytic activity and selectivity of supported nano-particles. There are two papers, one a theoretical study and the other an experimental study, concerned with core level spectroscopies and a paper concerned with Raman imaging of a surface of a surface reaction. Surface electronic structure theory for the analysis of catalytic reactions is also represented by two papers. Two papers deal with fundamental aspects of the technologically important catalytic production of hydrogen. These papers point the way to a future with an ample supply of energy. One paper is concerned with the properties of the surfaces of actinide oxides, materials with a potential for substantial catalytic activity. Finally, it is noted that two papers specifically address the properties and catalytic activity of metal nanoparticles. H. Idriss Department of Chemistry, University of Aberdeen, Aberdeen, UK

Doped Graphene as a Metal‐Free Carbocatalyst for the Selective Aerobic Oxidation of Benzylic Hydrocarbons, Cyclooctane and Styrene

Nitrogen (N)-, boron (B)-, and boron,nitrogen (B,N)-doped graphene (G) act as carbocatalysts, promoting the aerobic oxidation of the benzylic positions of aromatic hydrocarbons and cyclooctane to the corresponding alcohol/ketone mixture with more than 90 % selectivity. The most active material was the co-doped (B,N)G, which, in the absence of solvent and with a substrate/(B,N)G ratio of 200, achieved 50 % tetralin conversion in 24 h with a alcohol/ketone selectivity of 80 %. An FT-Raman spectroscopic study of a sample of (B,N)G heated at 100 °C in the presence of oxygen revealed new bands that disappeared upon evacuation and that have been attributed to hydroperoxide-like species formed on the G sheet based on the isotopic shift of the peak from 819 to 779 cm(-1) when (18)O2 was used as the oxidizing reagent. Furthermore, (B)G and (N)G exhibited high catalytic activity in the aerobic oxidation of styrene to benzaldehyde (BA) in 4 h. However, the product distribution changed over time and after 10 h a significant percentage of styrene oxide (SO) was observed under the same conditions. The use of doped G as catalyst appears to offer broad scope for the aerobic oxidation of benzylic compounds and styrene, for which low catalyst loading, mild reaction temperatures, and no additional solvents are required.

Nanoaggregates of Simple Mn Porphyrin Complexes as Catalysts for the Selective Oxidation of Hydrocarbons

AbstractA stable suspension of simple manganese(III) meso‐tetraphenylporphyrin nanoaggregates was prepared by a host–guest procedure, in which ethanol and water are used as “green” solvents. The organic nanoparticles were studied by dynamic light scattering (DLS), AFM, and UV/Vis and fluorescence spectroscopy. The results indicate that the nanoaggregates have a spherical morphology with sizes between 15–40 nm. The epoxidation of olefins and oxygenation of saturated hydrocarbons by PhI(OAc)2 were efficiently enhanced with excellent selectivity under the influence of simple Mn(TPP)OAc (TPP = meso‐tetraphenylporphyrin) nanoparticles. Enhanced stabilities and activities were achieved with nanostructured Mn catalysts compared to those of the individual counterparts in solution according to turnover numbers and UV/Vis studies. The title nanocatalyst facilitates a greener reaction because the reaction solvent is a water/ethanol mixture and PhI(OAc)2 is safe to use. The efficiency of the oxidation system depends critically upon the steric hindrances and electronic structures of both nitrogen donor ligands and porphyrin nanoparticles.

Solvent-free aerobic oxidation of hydrocarbons and alcohols with Pd@N-doped carbon from glucose

The development of efficient systems for selective aerobic oxidation of hydrocarbons and alcohols to produce more functional compounds (aldehydes, ketones, acids or esters) with atmospheric air or molecular oxygen is a grand challenge for the chemical industry. Here we report the synthesis of palladium nanoparticles supported on novel nanoporous nitrogen-doped carbon, and their impressive performance in the controlled oxidation of hydrocarbons and alcohols with air. In terms of catalytic activity, these catalysts afford much higher turnover frequencies (up to 863 turnovers per hour for hydrocarbon oxidation and up to ~210,000 turnovers per hour for alcohol oxidation) than most reported palladium catalysts under the same reaction conditions. This work provides great potential for the application of ambient air and recyclable palladium catalysts in fine-chemical production with high activity.

Oxo complexes of high-valence iron in oxidation catalysis

This review deals with oxo complexes of high-valence iron (oxoferryl, or simply ferryl complexes), which play an important role in the selective oxidation of hydrocarbons and other organic compounds. The efficiency and high selectivity of natural oxygenases stimulates researchers to design chemical analogues of these systems. Since the advantages of biological and biomimetic oxidation are due to the participation of ferryl intermediates, we will consider the ways of obtaining relatively stable oxo complexes of high-valence iron and their geometric and electronic structure and reactivity.

Rare Earth‐doped Ceria Catalysts for ODHE Reaction in a Catalytic Modified MIEC Membrane Reactor

AbstractAn intensification process for the selective oxidation of hydrocarbons integrates a catalytic reactor and an oxygen separation membrane. This work presents the study of oxidative dehydrogenation of ethane at 1123 K in a catalytic membrane reactor based on mixed ionic‐electronic conducting (MIEC) membranes. The surface of a membrane made of Ba0.5Sr0.5Co0.8Fe0.2O3−δ has been activated using different porous catalytic layers based on rare earth‐doped cerias (fluorite structure) and the porous catalytic coating was deposited by screen printing (coating around 15 μm). The different catalyst formulations were developed by partial substitution of Ce and were synthesized by co‐precipitation followed by cobalt impregnation when required. Specifically, seven different catalysts based on the system Ce1−xLnxO2−δ (x=0.1 or 0.2; Ln=Tb, Pr, Er, Gd, and Tb+Er), including the effect of cobalt addition (2 % molar) in Ce0.8Tb0.2O2−δ, were studied. The ceria catalysts were studied by XRD, SEM, DC‐conductivity as a function of oxygen partial pressure, and the high‐temperature stability in a CO2 environment was assessed using thermogravimetry. Then, the influence of the ceria catalytic coating on the oxygen permeation flux through the MIEC membrane was studied using argon and methane as the sweep gas in the permeate side. Finally, oxidative dehydrogenation of ethane reaction tests were performed at 1123 K, as a function of the ethane concentration in the feed. The use of a disk‐shaped membrane in the reactor made it possible to prevent the direct contact of gaseous oxygen and hydrocarbons and thus to increase the ethylene yield. High ethylene yields (up to ≈84 %) were obtained using a catalytic coating based on 20 % Tb‐doped ceria including macropores produced by the addition of graphite platelets in the screen printing ink. The high yields obtained in this kind of catalytic membrane are attributed to the combination of: the high catalytic activity; the control of the oxygen concentration in the gas phase (reaction chamber); and the appropriate fluid dynamics, enabling the fast ethylene evacuation.

ChemInform Abstract: Metal—Organic Frameworks of the MIL‐101 Family as Heterogeneous Single‐Site Catalysts

AbstractReview: 47 refs.