Selective Oxidation Of Alkanes Research Articles

Triphenylamine-based porous organic polymers: Synthesis and application for supporting phosphomolybdate to fabricate efficient olefin oxidation catalysts

Two kinds of triphenylamine-based porous organic polymers (POPs) were synthesized by FeCl3-triggered Friedel-Crafts polymerization of triphenylamine (TPA) and formaldehyde dimethylacetal (FDA) in the absence or presence of benzene (Ph), which are denoted as POP-I (without additional Ph) and POP-II (with additional Ph as linker), respectively. Various characterization results confirm the successful synthesis of TPA-based polymers with different bridged linkers and hierarchical pore structure. Phosphomolybdic acid (HPMA) and cobalt phosphomolybdate (CoPMA) were immobilized onto the POPs, to form phosphomolybdate (PMA) functionalized POPs catalysts, and their catalytic properties were investigated for the selective oxidation of olefins with H2O2. All the PMA functionalized POPs materials are catalytically active for the epoxidation/oxidation of olefins, while CoPMA/POP-II shows the highest activity, stability and recyclability. TPA-based POPs have distinctive electron-donating and transferring ability, which can be further tuned by introducing more bridged linkers of -Ph and -CH2 groups. Multi-interactions between PMA and POPs supports could be built through the electronic and geometric effects exerted by the 3-D POPs supports on the PMA clusters. Moreover, the existence of Co cations may further strengthen the interactions between PMA and POPs supports by forming electrostatic or coordination interactions with the TPA ligands, thus resulting in the high stability of the CoPMA/POP-II against leaching of active species during the H2O2 mediated catalytic oxidation process.

The first synthesis of Bi self-doped Bi2MoO6-Bi2Mo3O12 composites and their excellent photocatalytic performance for selective oxidation of aromatic alkanes under visible light irradiation.

We report the synthesis of Bi self-doped Bi2MoO6-Bi2Mo3O12 composites with heterostructures by a one-step method using Bi3.64Mo0.36O6.55 as precursor. Among them, Bi2.1MoO6-Bi2.1Mo3O12 shows excellent selectivity as well as recyclability in the oxidation of aromatic alkanes to aldehydes under visible light irradiation.

Reactions catalyzed by a binuclear copper complex: selective oxidation of alkenes to carbonyls with O2

A binuclear copper complex bearing a simple salicylate ligand catalyses the efficient cleavage of styrenes into ketones and aldehydes with O2 as the oxidant. The reaction works under an atmosphere of O2 (balloon) with 0.5 mol% of catalyst and could be performed on a gram scale, providing an alternative to ozonolysis.

Hybrid compounds assembled from copper-triazole complexes and phosphomolybdic acid as advanced catalysts for the oxidation of olefins with oxygen.

Two hybrid compounds, namely [Cu(3atrz)4][PMoMoVO40] (1) and [Cu(3atrz)6][PMo12O40]2 (2), were synthesized through hydrothermal reactions of 3-amino-1,2,4-triazole (3atrz), phosphomolybdic acid (PMA) and appropriate copper salts. Crystal structure analysis reveals that compound 1 contains one-dimensional Cu-3atrz chains. The unit of compound 2 contains a double calyx[3]arene-shaped hexamer, which is composed of six two-coordinated CuI atoms and six 3atrz ligands. Both compounds 1 and 2 present a three-dimensional hybrid structure, which is built by the self-assembly of Cu-3atrz clusters and Keggin-type PMA units. The resulting hybrid compounds can act as highly efficient heterogeneous catalysts for the selective oxidation of olefins with molecular oxygen as the oxidant in the presence of a trace amount of tert-butyl hydroperoxide (t-BuOOH). Their excellent catalytic properties can be mainly attributed to the existence of stabilized CuI complexes with an appropriate chemical environment and a spacious structure, which can interact with t-BuOOH to form catalytic sites for the direct activation of O2. This work demonstrates that the hybrid compounds assembled from copper-3atrz complexes and phosphomolybdic acid may have great potential in molecular O2-mediated catalytic oxidation reactions, which can certainly build a platform for deep insight into the biologically relevant catalytic oxidation processes.

Mesoporous Assembled Mn3 O4 Nanoparticle Networks as Efficient Catalysts for Selective Oxidation of Alkenes and Aryl Alkanes.

The design of nanoscale materials has been considered important for enhancing their surface properties for catalysis. Metal oxide nanoparticles have a large number of exposed surface active sites, but they suffer from low reactivity and poor stability resulting from excessive aggregation into less active microscopic structures. Herein, the synthesis of mesoporous Mn3 O4 nanoparticle assemblies by polymer-assisted self-assembly is presented and their catalytic activity is demonstrated in the oxidation of various saturated and unsaturated hydrocarbons, including aromatic alkenes and aryl alkanes, in the presence of tert-butyl hydroperoxide as a mild oxidant. It is also shown through comparative studies that the high catalytic activity and stability of these Mn3 O4 assemblies arise from the unique three-dimensional open-pore structure, high internal surface area (90 m2 g-1 ) and uniform mesopores (≈6.6 nm in size).

Selective epoxidation of cyclohexene with molecular oxygen on catalyst of nanoporous Au integrated with MoO3 nanoparticles

Selective oxidation of olefins to desired products such as epoxides is highly demanded in chemical industry. It remains challenging to achieve high selectivity for production of epoxides over heterogeneous catalysts through using molecular oxygen as the oxidant. Nanoporous reverse catalysts (MoO3@np-Au) consisting of pure nanoporous gold (np-Au) and MoO3 nanoparticles anchored on Au ligaments were synthesized for selective oxidation of cyclohexene with molecular oxygen. By controlling the loading of molybdenum and thermal treatment condition, MoO3 nanoparticles with size of ∼5nm were uniformly anchored on the surface of gold ligaments (30–50nm) of pure nanoporous gold (np-Au). These synthesized MoO3@np-Au catalysts exhibited high selectivity of 58%–73% for production of cyclohexene oxide at conversion of 4%–11% of cyclohexene by using molecular oxygen as the oxidant. Compared to MoO3@np-Au, the selectivity for the production of cyclohexene oxide on pure np-Au catalyst is only 6% under the same catalytic condition as that on MoO3@np-Au. The observed high selectivity for production of cyclohexene oxide on MoO3@np-Au can be rationalized with a bi-functional mechanism of a reverse metal/oxide catalyst. The in-situ formed surface molybdenum oxo-peroxo species are suggested to be responsible for selective oxidation of cyclohexene to cyclohexene oxide, while the MoO3/Au interface activates molecular oxygen to regenerate the molybdenum oxo-peroxo active centers.

The Mechanism of Alkane Selective Oxidation by the M1 Phase of Mo–V–Nb–Te Mixed Metal Oxides: Suggestions for Improved Catalysts

We report here first principles predictions (density functional theory with periodic boundary conditions) of the structures, mechanisms, and activation barriers for the catalytic activation and functionalization of propane by the M1 phase of the Mitsubishi-BP America generation of Mo–V–Nb–Te–O mixed metal oxide (MMO) catalysts. Our calculations show that the reduction-coupled oxo activation (ROA) principle, which we reported at Irsee VI to play the critical role for the selective oxidation of n-butane to maleic anhydride by vanadium phosphorous oxide, also plays the critical role for the MMO activation of propane, as speculated during Irsee VI. However for MMO, this ROA principle involves Te=O and V rather than P=O and V. The ability of the Te=O bond to activate the propane CH bond depends sensitively upon the number of V atoms that are coupled through a bridging O to the Te=O center. Based on this ROA mechanism, we suggest synthetic procedures aimed at developing a single phase MMO catalyst with dramatically improved selectivity for ammoxidation. We also suggest a modified single phase composition suitable for simultaneous oxidative dehydrogenation of ethane and propane to ethene and propene, respectively, which is becoming more important with the increase in petroleum fracking. Moreover, we also suggest some organometallic molecules that activate alkane CH bonds through the ROA principle.

Catalytic Mechanism and Efficiency of Methane Oxidation by Hg(II) in Sulfuric Acid and Comparison to Radical Initiated Conditions

Methane conversion to methyl bisulfate by HgII(SO4) in sulfuric acid is an example of fast and selective alkane oxidation catalysis. Dichotomous mechanisms involving C–H activation and electron transfer have been proposed based on experiments. Radical oxidation pathways have also been proposed for some reaction conditions. HgII is also of significant interest because as a d10 transition metal it is similar to d10 main-group metals that also oxidize alkanes. Density-functional calculations are presented that use both implicit and a mixture of implicit/explicit solvent models for the complete HgII catalytic cycle of methane oxidation to methyl bisulfate. These calculations are consistent with experiment and reveal that methane is functionalized to methyl bisulfate by a C–H activation and reductive metal alkyl functionalization mechanism. This reaction pathway is lower in energy than both electron transfer and proton-coupled electron transfer pathways. After methane C–H functionalization, catalysis is comple...

Ni-based catalysts derived from a metal-organic framework for selective oxidation of alkanes

Ni nanoparticles embedded in nitrogen-doped carbon (Ni@C-N) materials were prepared by thermolysis of a Ni-containing metal-organic framework (Ni-MOF) under inert atmosphere. The as-synthesized Ni@C-N materials were characterized by powder X-ray diffraction, N2 adsorption-desorption analysis, scanning electron microscopy, transmission electron microscopy, atomic absorption spectroscopy, and X-ray photoelectron spectroscopy. The MOF-derived Ni-based materials were then examined as heterogeneous catalysts for the oxidation of alkanes under mild reaction conditions. The Ni@C-N composites displayed high activity and selectivity toward the oxidation of a variety of saturated C–H bonds, affording the corresponding oxidation products in good-to-excellent yields. Furthermore, the catalysts could be recycled and reused for at least four times without any significant loss in activity and selectivity under the investigated conditions.

An Overview of Recent Advances of the Catalytic Selective Oxidation of Ethane to Oxygenates

The selective partial oxidation of short chain alkanes is a key challenge within catalysis research. Direct ethane oxidation to oxygenates is a difficult aim, but potentially rewarding, and it could lead to a paradigm shift in the supply chain of several bulk chemicals. Unfortunately, low C–H bond reactivity and kinetically labile products are just some reasons affecting the development and commercialisation of such processes. Research into direct ethane oxidation is therefore disparate, with approaches ranging from oxidation in the gas phase at high temperatures to enzyme catalysed hydroxylation under ambient conditions. Furthermore, in overcoming the barrier posed by the chemically inert C–H bond a range of oxidants have been utilised. Despite years of research, this remains an intriguing topic from both academic and commercial perspectives. Herein we describe some recent developments within the field of catalytic ethane oxidation focusing on the formation of oxygenated products, whilst addressing the key challenges which are still to be overcome.

Effect of cis/trans isomerism on selective oxidation of olefins with nitrous oxide

Liquid phase oxidation of olefins with nitrous oxide is a promising synthetic route to ketones. The effect of cis/trans isomerism on the reactivity of olefins towards N2O and on the reaction mechanism was studied for the first time using 3-heptene oxidation as an example. Our experimental study revealed that cis- and trans-isomers of 3-heptene have similar reactivity and yield the same set of products. However, the cis/trans isomerism of the olefin has a pronounced effect on the reaction route involving the cleavage of the initial CC bond and, accordingly, on the products ratio. The yield of ketones is lower for the trans-isomer due to higher contribution of the cleavage route.

Selective Alkane Oxidation by Manganese Oxide: Site Isolation of MnOx Chains at the Surface of MnWO4 Nanorods

The electronic and structural properties of vanadium-containing phases govern the formation of isolated active sites at the surface of these catalysts for selective alkane oxidation. This concept is not restricted to vanadium oxide. The deliberate use of hydrothermal techniques can turn the typical combustion catalyst manganese oxide into a selective catalyst for oxidative propane dehydrogenation. Nanostructured, crystalline MnWO4 serves as the support that stabilizes a defect-rich MnOx surface phase. Oxygen defects can be reversibly replenished and depleted at the reaction temperature. Terminating MnOx zigzag chains on the (010) crystal planes are suspected to bear structurally site-isolated oxygen defects that account for the unexpectedly good performance of the catalyst in propane activation.

Nitrogen, Phosphorus, and Sulfur Co-Doped Hollow Carbon Shell as Superior Metal-Free Catalyst for Selective Oxidation of Aromatic Alkanes.

Metal-free heteroatom-doped carbocatalysts with a high surface area are desirable for catalytic reactions. In this study, we found an efficient strategy to prepare nitrogen, phosphorus, and sulfur co-doped hollow carbon shells (denote as NPS-HCS) with a surface area of 1020 m(2) g(-1). Using a poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (PZS) shell as carbon source and N, P, S-doping source, and the ZIF-67 core as structural template as well as extra N-doping source, NPS-HCS were obtained with a high surface area and superhydrophilicity. All these features render the prepared NPS-HCS a superior metal-free carbocatalyst for the selective oxidation of aromatic alkanes in aqueous solution. This study provides a reliable and facile route to prepare doped carbocatalysts with enhanced catalytic properties.

Nitrogen, Phosphorus, and Sulfur Co‐Doped Hollow Carbon Shell as Superior Metal‐Free Catalyst for Selective Oxidation of Aromatic Alkanes

AbstractMetal‐free heteroatom‐doped carbocatalysts with a high surface area are desirable for catalytic reactions. In this study, we found an efficient strategy to prepare nitrogen, phosphorus, and sulfur co‐doped hollow carbon shells (denote as NPS‐HCS) with a surface area of 1020 m2 g−1. Using a poly(cyclotriphosphazene‐co‐4,4′‐sulfonyldiphenol) (PZS) shell as carbon source and N, P, S‐doping source, and the ZIF‐67 core as structural template as well as extra N‐doping source, NPS‐HCS were obtained with a high surface area and superhydrophilicity. All these features render the prepared NPS‐HCS a superior metal‐free carbocatalyst for the selective oxidation of aromatic alkanes in aqueous solution. This study provides a reliable and facile route to prepare doped carbocatalysts with enhanced catalytic properties.

Synthesis, characterization, and catalytic activity of supported molybdenum Schiff base complex as a magnetically recoverable nanocatalyst in epoxidation reaction

A heterogeneous nanocatalyst was prepared via covalent anchoring of dioxomolybdenum(VI) Schiff base complex on core–shell structured Fe3O4@SiO2. The properties and the nature of the surface-fixed complex have been identified by a series of characterization techniques such as SEM, EDX, XRD, TGA, FT-IR, and VSM. The synthesized hybrid material was an efficient nanocatalyst for selective oxidation of olefins to corresponding epoxides with t-BuOOH in high yields and selectivity. The catalyst could be conveniently recovered by applying an external magnetic field and reused several times without significant loss of efficiency.

ChemInform Abstract: Green and Efficient: Iron‐Catalyzed Selective Oxidation of Olefins to Carbonyls with O2.

AbstractA broad range of α‐ and β‐substituted styrene derivatives is chemoselectively oxidized to the corresponding aromatic aldehydes or ketones.

Nitrogen, phosphorus and sulfur co-doped ultrathin carbon nanosheets as a metal-free catalyst for selective oxidation of aromatic alkanes and the oxygen reduction reaction

Nitrogen, phosphorus and sulfur co-doped ultrathin carbon nanosheets showed outstanding activity for selective oxidation and oxygen reduction reaction.

Design and synthesis of nanoporous perylene bis-imide linked metalloporphyrin frameworks and their catalytic activity

Two nanoporous perylene bis-imide linked metalloporphyrin framework catalysts have been synthesized via condensation of 5,10,15,20-tetrakis-(4\(^{\prime }\)-aminophenyl) iron(III) porphyrin chloride or 5,10, 15,20-tetrakis-(4\(^{\prime }\)-aminophenyl) manganese(III) porphyrin chloride with perylene-3,4,9,10-tetracarboxylic dianhydride. Both the materials were crystalline in nature and were characterized by electron microscopy techniques, solid-state 1H- 13C CP/MS NMR, powder X-ray diffraction (PXRD), and magnetic susceptibility measurements. The nitrogen gas physisorption study has indicated that both materials are porous in nature and have BET surface area with 653 m2/g and 974 m2/g with uniform pore size of 2.8 nm. These materials were found to act as very good heterogeneous catalysts for selective oxidation of alkanes and alkenes with tert-butyl hydroperoxide and were not degraded even after multiple uses up to 10 cycles. Two nanoporous perylene bis-imide linked metalloporphyrin framework catalysts have been synthesized. They show interesting peroxidase activity for the selective oxidation of alkanes and alkenes even after ten cycles with negligible catalyst degradation.

Selective oxidation of olefins with aqueous hydrogen peroxide over phosphomolybdic acid functionalized knitting aryl network polymer

A phosphomolybdic acid (PMA)-based heterogeneous catalyst, denoted as PMA/KAP, was prepared by immobilizing PMA onto a knitting aryl network polymer (KAP) based on triphenylphosphine (PPh3). The catalytic property of PMA/KAP was investigated for the selective oxidation of olefins with aqueous hydrogen peroxide (H2O2) as oxidant. When using ethyl acetate (EAC) as reaction medium, PMA/KAP performs higher activity and selectivity to epoxide for a variety of olefins, and it can be reused for several times without obvious loss of activity. When the reaction was carried out in acetonitrile (AN) medium, deactivation of PMA/KAP catalyst can be observed immediately. A variety of characterization results suggest that the degradation of PMA unit to (PO4[MoO(O2)2]4)3− occurs easily when the PMA/KAP catalyst is operated in H2O2/AN system, while such degradation behavior could be significantly inhibited when the catalyst is used in the system of H2O2/EAC. We proposed that the neighbouring P-containing ligands dispersed in the framework of KAP can produce a steric pocket with low electron density, which can promote the formation of multi-weak coordination interaction between PMA unit and several P ligands. Such multi-weak interaction can inhibit the degradation of PMA to (PO4[MoO(O2)2]4)3−, thus avoiding the leaching of active species from the KAP support, and resulting in the formation of relatively stable heterogeneous PMA supported catalyst for olefin epoxidation with H2O2 in the media of EAC.

Hierarchical flower-like Co–Cu mixed metal oxide microspheres as highly efficient catalysts for selective oxidation of ethylbenzene

The selective oxidation of alkanes and alkylaromatics to corresponding alcohols, ketones or carboxylic acids is of great importance for the production of high added-value raw materials in the fine chemical industry. The design and synthesis of cost-effective and recyclable heterogeneous oxidation catalysts has become one of the most active research areas. In this work, a series of novel Al2O3@Co–Cu–Al mixed metal oxide (Al2O3@CoCuAl-MMO) catalysts with hierarchical flower-like microstructure were successfully prepared via a Co–Cu–Al layered double hydroxide precursor route, and their catalytic performance was investigated in the liquid-phase selective oxidation of ethylbenzene using tert-butyl hydroperoxide as oxidant without the addition of any organic solvents. The characterization results revealed that the incorporation of copper into the MMO could induce the formation of the interactions between the Co–Cu species, and thus catalytic performance of as-formed Al2O3@CoCuAl-MMO catalysts was significantly promoted. In the selective oxidation of ethylbenzene, a high conversion of 92.8% with an acetophenone selectivity of 89.4% was achieved over the Al2O3@CoCuAl-MMO catalyst with a Cu/(Cu+Co) molar ratio of 0.25. The high catalytic efficiency was attributed mainly to the synergistic effect between highly dispersed active Co and Cu species. More importantly, the obtained catalysts having good recyclability and stability displayed good catalytic performance in the oxidation of other alkanes and alkylaromatics including 1,2,3,4-tetrahydronaphthalene, toluene, cumene, and methylcyclohexane.