Alkane Activation Research Articles

High Diversity of Anaerobic Alkane-Degrading Microbial Communities in Marine Seep Sediments Based on (1-methylalkyl)succinate Synthase Genes.

Alkanes comprise a substantial fraction of crude oil and are prevalent at marine seeps. These environments are typically anoxic and host diverse microbial communities that grow on alkanes. The most widely distributed mechanism of anaerobic alkane activation is the addition of alkanes to fumarate by (1-methylalkyl)succinate synthase (Mas). Here we studied the diversity of MasD, the catalytic subunit of the enzyme, in 12 marine sediments sampled at seven seeps. We aimed to identify cosmopolitan species as well as to identify factors structuring the alkane-degrading community. Using next generation sequencing we obtained a total of 420 MasD species-level operational taxonomic units (OTU0.96) at 96% amino acid identity. Diversity analysis shows a high richness and evenness of alkane-degrading bacteria. Sites with similar hydrocarbon composition harbored similar alkane-degrading communities based on MasD genes; the MasD community structure is clearly driven by the hydrocarbon source available at the various seeps. Two of the detected OTU0.96 were cosmopolitan and abundant while 75% were locally restricted, suggesting the presence of few abundant and globally distributed alkane degraders as well as specialized variants that have developed under specific conditions at the diverse seep environments. Of the three MasD clades identified, the most diverse was affiliated with Deltaproteobacteria. A second clade was affiliated with both Deltaproteobacteria and Firmicutes likely indicating lateral gene transfer events. The third clade was only distantly related to known alkane-degrading organisms and comprises new divergent lineages of MasD homologs, which might belong to an overlooked phylum of alkane-degrading bacteria. In addition, masD geneFISH allowed for the in situ identification and quantification of the target guild in alkane-degrading enrichment cultures. Altogether, these findings suggest an unexpectedly high number of yet unknown groups of anaerobic alkane degraders and underline the need for comprehensive surveys of microbial diversity based on metabolic genes in addition to ribosomal genes.

25th Annual Saudi-Japan Symposium: Catalysts in Petroleum Refining and Petrochemicals, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia, December 7–8, 2015

More than 100 scientists, engineers, catalyst experts and researchers from Japan, Saudi Arabia, Spain, and the Czech Republic, participated in the two-day symposium on catalysts used in petroleum refining and petrochemicals held on December 7–8, 2015 at King Fahd University of Petroleum & Minerals (KFUPM), Dhahran, Saudi Arabia. The annual symposium was jointly organized by KFUPM, Saudi Aramco, the Japan Petroleum Institute (JPI) and Japan Cooperation Center, Petroleum (JCCP) to discuss latest advances in catalysts for refining and chemical processing. The year 2005 marked the silver jubilee 25th anniversary of the Symposium and the 60th years of establishing diplomatic ties between Saudi Arabia and Japan. Seventeen presentations featured topics on the activation of light alkanes, aromatics, chemicals from CO2, olefins, photocatalysis, fuel upgrade, carbenes, membranes and polyolefins. The following is a brief report on the topics covered by the symposium.

From DNA to catalysis: a thymine-acetate ligated non-heme iron(III) catalyst for oxidative activation of aliphatic C-H bonds.

A non-heme, iron(III)/THA(thymine-1-acetate) catalyst together with H2O2 as an oxidant is efficient in oxidative C-H activation of alkanes. Although having a higher preference for tertiary C-H bonds, the catalyst also oxidizes aliphatic secondary C-H bonds into carbonyl compounds with good to excellent conversions. Based on the site selectivity of the catalyst and our mechanistic studies the reaction proceeds via an Fe-oxo species without long lived carbon centered radicals.

To rebound or dissociate? This is the mechanistic question in C-H hydroxylation by heme and nonheme metal-oxo complexes.

Enzymatic reactions that involve C-H bond activation of alkanes by high-valent iron-oxo species can be explained by the rebound mechanism (RM). Hydroxylation reactions of alkane substrates effected by the reactive compound I (Cpd I) species of cytochrome P450 enzymes are good examples. There was initially little doubt that the rebound paradigm could be carried over in the same form to the arena of synthetic nonheme high-valent iron-oxo or other metal-oxo complexes. However, the active reaction centres of these synthetic systems are not well-caged, in contrast to the active sites of enzymes; therefore, the relative importance of the radical dissociation pathway can become prominent. Indeed, accumulating experimental and theoretical evidence shows that introduction of the non-rebound mechanism (non-RM) is necessary to rationalise the different reactivity patterns observed for synthetic nonheme complexes. In this tutorial review, we discuss several specific examples involving the non-RM while making frequent comparisons to the RM, mainly from the perspective of computational chemistry. We also provide a technical guide to DFT calculations of RM and non-RM and to the interpretations of computational outcomes.

Activation and Transformation of Ethane by Au2 VO3(+) Clusters with Closed-Shell Electronic Structures.

The study of chemical reactions between gold-containing heteronuclear oxide clusters and small molecules can provide molecular level mechanisms to understand the excellent activity of gold supported by metal oxides. While the promotion role of gold in alkane transformation was identified in the clusters with atomic oxygen radicals (O(-.)), the role of gold in the systems without O(-.) is not clear. By employing mass spectrometry and quantum chemistry calculations, the reactivity of Au2 VO3(+) clusters with closed-shell electronic structures toward ethane was explored. Both the dehydrogenation and ethene elimination channels were identified. It is gold rather than oxygen species initiating the C-H activation. The Au-Au dimer formed during the reactions plays important roles in ethane transformation. The reactivity comparison between Au2 VO3(+) and bare Au2(+) demonstrates that Au2 VO3(+) not only retains the property of bare Au2(+) that transforming ethane to dihydrogen, but also exhibits new functions in converting ethane to ethene, which reveals the importance of the composite system. This study provides a further understanding of the reactivity of metal oxide supported gold in alkane activation and transformation.

A density functional theory study on the effect of silica support: Methane activation on nickel oxide clusters through a radical mechanism

Supported transition metal catalysts belong to an important family of catalyst in chemical industry, making the support effect to be a important issue in fundamental research. A theoretical computation using density functional theory (DFT) was performed to investigate the support effect of a silica model on the initial step of methane activation on NixOx (where, x=2, 3) clusters. The behavior of four reactions were studied by exploring their potential energy surfaces (PES), namely, (i) CH4 reacting with an unsupported Ni2O2 cluster, (ii) with a silica-supported Ni2O2 cluster, (iii) with an unsupported Ni3O3 cluster, and (iv) with an silica-supported Ni3O3 cluster. For each of these four reactions, only a radical mechanism was investigated, and the PESs with different spin states were explored. A spin transition process is involved for the reactions on the unsupported NixOx clusters, and no spin transition is required for the case of supported NixOx clusters. The reaction barrier as well as the reaction free energy is increased with the involvement of the model silica support. These results provide a deeper insight into the support effect on the CH bond activation of small alkanes in general and of methane in particular on supported transition metal catalysts.

Ubiquitous Presence and Novel Diversity of Anaerobic Alkane Degraders in Cold Marine Sediments.

Alkanes are major constituents of crude oil and are released to the marine environment by natural seepage and from anthropogenic sources. Due to their chemical inertness, their removal from anoxic marine sediments is primarily controlled by the activity of anaerobic alkane-degrading microorganisms. To facilitate comprehensive cultivation-independent surveys of the diversity and distribution of anaerobic alkane degraders, we designed novel PCR primers that cover all known diversity of the 1-methylalkyl succinate synthase gene (masD/assA), which catalyzes the initial activation of alkanes. We studied masD/assA gene diversity in pristine and seepage-impacted Danish coastal sediments, as well as in sediments and alkane-degrading enrichment cultures from the Middle Valley (MV) hydrothermal vent system in the Pacific Northwest. MasD/assA genes were ubiquitously present, and the primers captured the diversity of both known and previously undiscovered masD/assA gene diversity. Seepage sediments were dominated by a single masD/assA gene cluster, which is presumably indicative of a substrate-adapted community, while pristine sediments harbored a diverse range of masD/assA phylotypes including those present in seepage sediments. This rare biosphere of anaerobic alkane degraders will likely increase in abundance in the event of seepage or accidental oil spillage. Nanomolar concentrations of short-chain alkanes (SCA) were detected in pristine and seepage sediments. Interestingly, anaerobic alkane degraders closely related to strain BuS5, the only SCA degrader in pure culture, were found in mesophilic MV enrichments, but not in cold sediments from Danish waters. We propose that the new masD/assA gene lineages in these sediments represent novel phylotypes that are either fueled by naturally occurring low levels of SCA or that metabolize medium- to long-chain alkanes. Our study highlights that masD/assA genes are a relevant diagnostic marker to identify seepage and microseepage, e.g., during prospecting for oil and gas, and may act as an indicator of anthropogenic oil spills in marine sediments.

Contrasting Mechanisms and Reactivity of Tl(III), Hg(II), and Co(III) for Alkane C–H Functionalization

Activation and functionalization of alkane C–H bonds has historically been dominated by transition-metal complexes. Light alkanes can also be partially oxidized by sixth-row main-group compounds, such as TlIII(TFA)3 (TFA = trifluoroacetate). Here we present density-functional calculations which demonstrate that TlIII(TFA)3 oxidizes alkanes by closed-shell C–H activation and Tl–alkyl functionalization mechanisms. The discovery of a C–H activation pathway is surprising, because TlIII often oxidizes arene C–H bonds through an electron transfer mechanism and the transition-metal complex CoIII(TFA)3, with similar oxidation state and ligand coordination, oxidizes alkanes via an open-shell radical mechanism. Comparison of TlIII(TFA)3 to the transition-metal analogue IrIII(TFA)3 reveals that key to TlIII oxidation of alkanes is a moderate barrier for C–H bond activation that is lower in energy than open-shell pathways and a subsequent metal–alkyl functionalization reaction step with a very low barrier. Our calcul...

The effect of a silica support: a density functional theory study of the C-H bond activation of ethane on a nickel oxide cluster

The support effect is an important issue in heterogeneous catalysis. A systematic density functional theory computational study is reported here to better understand the C–H bond activation steps in the reaction between C2H6 and a model silica-supported Ni3O3 cluster, as well as that between C2H6 and an unsupported Ni3O3 cluster. Two mechanisms, namely, a radical mechanism (denoted as mechanism A) and a concerted mechanism (denoted as mechanism B) were examined. Both of these mechanisms contain two steps. For the C–H bond activation taking place via mechanism A, the involvement of the model silica support does not change the most favorable pathway significantly; however, it does result in a modest increase in the reaction barrier and the overall Gibbs energy change. For the C–H bond activation taking place via mechanism B, the involvement of the model silica support leads to an increase in the reaction barrier in the first step. The product of this step has a noticeable difference in the structures for the Ni3O3 moiety in the unsupported and model silica-supported systems. The result of charge analysis shows that there is no noticeable charge transfer between the silica support and Ni3O3 when they are in the starting reactants, while there is an electron withdrawal from Ni3O3 by the silica support when they are in transition states, intermediates, or products. The results here provide deeper insights into the support effect on the C–H bond activation of lower alkanes on supported transition metal catalysts. Copyright © 2015 John Wiley & Sons, Ltd.

CH Bond Activation by Early Transition Metal Carbide Cluster Anion MoC3−

Although early transition metal (ETM) carbides can activate CH bonds in condensed-phase systems, the electronic-level mechanism is unclear. Atomic clusters are ideal model systems for understanding the mechanisms of bond activation. For the first time, CH activation of a simple alkane (ethane) by an ETM carbide cluster anion (MoC3 (-) ) under thermal-collision conditions has been identified by using high-resolution mass spectrometry, photoelectron imaging spectroscopy, and high-level quantum chemical calculations. Dehydrogenation and ethene elimination were observed in the reaction of MoC3 (-) with C2 H6 . The CH activation follows a mechanism of oxidative addition that is much more favorable in the carbon-stabilized low-spin ground electronic state than in the high-spin excited state. The reaction efficiency between the MoC3 (-) anion and C2 H6 is low (0.23±0.05) %. A comparison between the anionic and a highly efficient cationic reaction system (Pt(+) +C2 H6 ) was made. It turned out that the potential-energy surfaces for the entrance channels of the anionic and cationic reaction systems can be very different.

ChemInform Abstract: Stable Organoplatinum Complexes as Intermediates and Models in Hydrocarbon Functionalization

AbstractReview: 151 refs.

DFT studies on the activation of C–H bonds on V/P mixed oxides

We carried out DFT calculations on the activation of C–H bonds on V/P mixed oxides. A set of oxo clusters, V4−xPxO10 (x = 0–4), used as model catalysts showed that the PO–H bond was stronger than the VO–H bond and the proton was preferentially bonded to the P=O bond. However, for alkane activation, the P=O was not the active site as expected because the activation requires a large reorganization energy. In addition, the results showed that the P=O bond played a role in the activation of intermediates with a more acidic C–H bond, such as 2-butene and 2,5-dihydrofuran.

Ethane and propane dehydrogenation over PtIr/Mg(Al)O

Increased demand for light alkenes has motivated research on the catalytic dehydrogenation of the light alkanes and on understanding the role of catalyst composition on the activity, selectivity, and stability of Pt-based catalysts used for this purpose. The present study examines the structure and performance of Pt–Ir catalysts for ethane and propane dehydrogenation, and compares them with the performance of Pt and Pt–Sn catalysts. Nanoparticles of Pt, PtSn, and PtIr were prepared in a colloidal suspension and then dispersed onto calcined hydrotalcite (Mg(Al)O). After characterization to confirm formation of a bimetallic alloy, it was observed that at high conversions, Pt3Ir/Mg(Al)O exhibited lower initial activity than Pt3Sn/Mg(Al)O but greater stability to coke deposition. Intrinsic rate measurements at low feed residence time revealed the following trend in activity: Pt3Sn>Pt3Ir>Pt. DFT calculations carried out on tetrahedral clusters (Pt4, Pt3Ir, Pt3Sn) reveals that this trend in activity can be replicated and Ir is capable of alkane activation, a trait unique to this bimetallic system.

Contrasting electronic requirements for C-H binding and C-H activation in d(6) half-sandwich complexes of rhenium and tungsten.

A computational study of the interaction half-sandwich metal fragments (metal = Re/W, electron count = d(6)), containing linear nitrosyl (NO(+) ), carbon monoxide (CO), trifluorophosphine (PF3 ), N-heterocyclic carbene (NHC) ligands with alkanes are conducted using density functional theory employing the hybrid meta-GGA functional (M06). Electron deficiency on the metal increases with the ligand in the order NHC < CO < PF3 < NO(+). Electron-withdrawing ligands like NO(+) lead to more stable alkane complexes than NHC, a strong electron donor. Energy decomposition analysis shows that stabilization is due to orbital interaction involving charge transfer from the alkane to the metal. Reactivity and dynamics of the alkane fragment are facilitated by electron donors on the metal. These results match most of the experimental results known for CO and PF3 complexes. The study suggests activation of alkane in metal complexes to be facile with strong donor ligands like NHC.

Thermal Chemistry of Cp*W(NO)(H)(η3-allyl) Complexes

The thermal properties of Cp*W(NO)(H)(η3-CH2CHCMe2) (1), Cp*W(NO)(H)(η3-CH2CHCHPh) (2), and Cp*W(NO)(H)(η3-CH2CHCHMe) (3) (Cp* = η5-C5Me5) have been investigated. Thermolyses of 1–3 in n-pentane lead to the loss of the original allyl ligand and the formation of the same mixture of isomeric products, namely, Cp*W(NO)(H)(η3-CH2CHCHEt) (4a) and Cp*W(NO)(H)(η3-MeCHCHCHMe) (4b) and their coordination isomers. Similarly, 1 reacts with cyclohexane and n-heptane to form Cp*W(NO)(H)(η3-C6H9) and isomers of Cp*W(NO)(H)(η3-C7H13), respectively. It is likely that complexes 1–3 first effect the selective, single-terminal C–H activation of the linear alkanes, but the first-formed products are thermally unstable and undergo two additional successive C–H activations to form the final allyl complexes. Consistent with this view is the fact that a bis(alkyl) intermediate complex can be trapped with N-methylmorpholine. Thus, the thermolysis of 1 in N-methylmorpholine affords a single organometallic complex, Cp*W(NO)(η2-CH2NC...

Anaerolineaceae and Methanosaeta turned to be the dominant microorganisms in alkanes-dependent methanogenic culture after long-term of incubation.

The methanogenic alkanes-degrading enrichment culture which had been incubated for over 1,300 days amended with n-alkanes (C15–C20) was investigated through clone libraries of bacteria, archaea and assA, mcrA functional genes. These enrichment cultures were obtained from oily sludge after an initial incubation of the oily sludge without any carbon source and then an enrichment transfer with n-alkanes (C15–C20) for acclimation. Activation of alkanes, methane precursor generation and methanogenic pathways are considered as three pivotal stages for the continuous methanogenesis from degradation of alkanes. The presence of functional genes encoding the alkylsuccinate synthase α-subunit indicated that fumarate addition is most likely the one of initial activation step for degradation of n-alkanes. Degradation intermediates of n-alkanes were octadecanoate, hexadecanoate, butyrate, isobutyrate, acetate and propionate, which could provide the appropriate substrates for acetate formation. Both methyl coenzyme M reductase gene and 16S rRNA gene analysis showed that microorganisms of Methanoseata were the most dominant methanogens, capable of using acetate as the electron donor to produce methane. Bacterial clone libraries showed organisms of Anaerolineaceae (within the phylum of Chloroflexi) were predominant (45.5%), indicating syntrophically cooperation with Methanosaeta archaea was likely involved in the process of methanogenic degradation of alkanes. Alkanes may initially be activated via fumarate addition and degraded to fatty acids, then converted to acetate, which was further converted to methane and carbon dioxide by methanogens.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-015-0117-4) contains supplementary material, which is available to authorized users.

ChemInform Abstract: Direct Construction of 2‐Alkylbenzo‐1,3‐azoles via C—H Activation of Alkanes for C—C and C—X (X: O, S) Bond Formation.

AbstractC‐2 alkylated benzo‐1,3‐thiazoles and ‐oxazoles are obtained by reaction of aryl isothiocyanates/isocyanates with simple alkanes in a catalytic, efficient, and cost‐effective manner.

Ruthenium Olefin Metathesis Catalysts Containing Fluoride

The reaction of the ruthenium complex cis-Caz-1 with silver fluoride affords the first example of an active olefin metathesis precatalyst containing fluoride ligands. The cis geometry of the precursor complex is key to the successful fluoride exchange reaction. Computational studies highlight the stability of the new Ru–F species, due to push–pull interactions between fluoride and L-type ligands (L: N-heterocyclic carbene, phosphite). Insights into the isomerization process from trans-Caz-1 to cis-Caz-1 are given. Fluoride exchange reactions were performed involving cis- and trans-Caz-1 complexes. Catalytic tests showcase the excellent activity of the Ru–F containing complexes.

Alkane Activation Initiated by Hydride Transfer: Co-conversion of Propane and Methanol over H-ZSM-5 Zeolite.

Co-conversion of alkane with another reactant over zeolite catalysts has emerged as a new approach to the long-standing challenge of alkane transformation. With the aid of solid-state NMR spectroscopy and GC-MS analysis, it was found that the co-conversion of propane and methanol can be readily initiated by hydride transfer at temperatures of ≥449 K over the acidic zeolite H-ZSM-5. The formation of (13)C-labeled methane and singly (13)C-labeled n-butanes in selective labeling experiments provided the first evidence for the initial hydride transfer from propane to surface methoxy intermediates. The results not only provide new insight into carbocation chemistry of solid acids, but also shed light on the low-temperature transformation of alkanes for industrial applications.

Alkane Activation Initiated by Hydride Transfer: Co‐conversion of Propane and Methanol over H‐ZSM‐5 Zeolite

AbstractCo‐conversion of alkane with another reactant over zeolite catalysts has emerged as a new approach to the long‐standing challenge of alkane transformation. With the aid of solid‐state NMR spectroscopy and GC‐MS analysis, it was found that the co‐conversion of propane and methanol can be readily initiated by hydride transfer at temperatures of ≥449 K over the acidic zeolite H‐ZSM‐5. The formation of 13C‐labeled methane and singly 13C‐labeled n‐butanes in selective labeling experiments provided the first evidence for the initial hydride transfer from propane to surface methoxy intermediates. The results not only provide new insight into carbocation chemistry of solid acids, but also shed light on the low‐temperature transformation of alkanes for industrial applications.