Butenes and butadiene, which are useful intermediates for the synthesis of polymers and other compounds, are synthesized traditionally by oxidative dehydrogenation (ODH) of n-butane over complex metal oxides. Such catalysts require high O 2 /butane ratios to maintain the activity, which leads to unwanted product oxidation. We show that carbon nanotubes with modified surface functionality efficiently catalyze the oxidative dehydrogenation of n-butane to butenes, especially butadiene. For low O 2 /butane ratios, a high selectivity to alkenes was achieved for periods as long as 100 hours. This process is mildly catalyzed by ketonic C=O groups and occurs via a combination of parallel and sequential oxidation steps. A small amount of phosphorus greatly improved the selectivity by suppressing the combustion of hydrocarbons.Transition metal oxides have been widely used as catalysts for the conversion of butane to C 4 alkenes, important industrial precursors for producing synthetic rubbers, plastics, and a number of industrially important chemicals. Despite a great deal of research, alkene selectivity in the current butane-to-butadiene process is severely limited (1). One important reason is that the unsaturated products are much more readily oxidized to CO 2 than is the starting alkane. The chemical complexity of polyvalent metal oxides, although found to be necessary for catalytic activity, impedes satisfactory selectivity through isolation of active sites (2-6). For this reason, the origin of the catalytic activity is debated, and there is as yet no generally accepted picture of the reaction mechanism (7, 8).Carbon materials have been reported to catalyze the oxidative dehydrogenation (ODH) of an aromatic molecule, ethylbenzene. However, conventional carbons, in particular activated carbon, underwent unavoidable deactivations due to coking or combustion (9-12). Recently, it was shown that only wellnanostructured carbons are stable and coke-free catalysts for styrene synthesis (12, 13). Activation of C-H bonds in the ethyl group is considered to be coordinated by the ketonic carbonyl (C=O) group. Ethylbenzene has an aromatic moiety that enables relatively facile activation. Here, we report on surfacemodified carbon nanotubes (CNTs) as a high-performance catalyst for the ODH of the much less active butane. Relative to metal-based catalysts, CNTs displayed an enhanced selectivity to C 4 alkenes, especially butadiene.We conducted the reaction at 400° or 450°C with an O 2 /butane ratio of 2.0. The product mixture contained only 1-butene, 2-butene, butadiene, CO 2 , CO, and residual reactants; the resulting carbon balance was 100 ± 3% ( fig. S1A) (14). In a blank experiment without catalyst, the alkene yield was as low as 0.9%. Over pristine CNTs, 88.9% of the converted butane was burnt, yielding 1.6% alkenes (Fig. 1A). Considering the intensive stability of CNTs in O 2 ( fig. S1B) (14), we conclude that the CO 2 during the reaction mainly originated from the oxidation of the hydrocarbon feedstock and not from burning of t...

The surface chemical properties and the electronic properties of vapor grown carbon nanofibers (VGCNFs) have been modified by treatment of the oxidized CNFs with NH(3). The effect of treatment temperature on the types of nitrogen functionalities introduced was evaluated by synchrotron based X-ray photoelectron spectroscopy (XPS), while the impact of the preparation methods on the surface acid-base properties was investigated by potentiometric titration, microcalorimetry, and zeta potential measurements. The impact of the N-functionalization on the electronic properties was measured by THz-Time Domain spectroscopy. The samples functionalized via amination are characterized by the coexistence of acidic and basic O and N sites. The population of O and N species is temperature dependent. In particular, at 873 K nitrogen is stabilized in substitutional positions within the graphitic structure, as heterocyclic-like moieties. The surface presents heterogeneously distributed and energetically different basic sites. A small amount of strong basic sites gives rise to a differential heat of CO(2) adsorption of 150 kJ mol(-1). However, when functionalization is carried out at 473 K, nitrogen moieties with basic character are introduced and the maximum heat of adsorption is significantly lower, at approximately 90 kJ mol(-1). In the latter sample, energetically different basic sites coexist with acidic oxygen groups introduced during the oxidative step. Under these conditions, a bifunctional acidic and basic surface is obtained with high hydrophilic character. N-functionalization carried out at higher temperature changes the electronic properties of the CNFs as evaluated by THz-TDS. The functionalization procedure presented in this work allows high versatility and flexibility in tailoring the surface chemistry of nanocarbon material to specific needs. This work shows the potential of the N-containing nanocarbon materials obtained via amination in catalysis as well as electronic device materials.

Low-temperature (∼450 °C), scalable chemical vapor deposition of predominantly monolayer (74%) graphene films with an average D/G peak ratio of 0.24 and domain sizes in excess of 220 μm(2) is demonstrated via the design of alloy catalysts. The admixture of Au to polycrystalline Ni allows a controlled decrease in graphene nucleation density, highlighting the role of step edges. In situ, time-, and depth-resolved X-ray photoelectron spectroscopy and X-ray diffraction reveal the role of subsurface C species and allow a coherent model for graphene formation to be devised.