At high temperatures, the oxidative coupling of methane (OCM) is an attractive approach for catalytic conversion of methane into value-added chemicals. Experiments with a Pt/Al2O3-coated catalytic honeycomb monolith were conducted with varying CH4/O2 ratios, N2 dilution at atmospheric pressure, and very short contact times. The reactor was modeled by a multiscale approach using a parabolic two-dimensional flow field description in the monolithic channels coupled with a heat balance of the monolithic structure, and multistep surface reaction mechanisms as well as elementary-step, gas phase reaction mechanisms. The contribution of heterogeneous and homogeneous reactions, both of which are important for the optimization of C2 products, is investigated using a combination of experimental and computational methods. The oxidation of methane, which takes place over the platinum catalyst, causes the adiabatic temperature increase required for the generation of CH3 radicals in the gas phase, which are essential for the formation of C2 species. Lower CH4/O2 ratios result in higher C2 selectivity. However, the presence of OH radicals at high temperatures facilitates subsequent conversion of C2H2 at a CH4/O2 ratio of 1.4. Thereby, C2 species selectivity of 7% was achieved at CH4/O2 ratio of 1.6, with 35% N2 dilution.

Abstract:In this work, the influence of the structure-forming agent on the composition, morphology and oxygen reduction reaction (ORR) activity of Fe-N-C catalysts was investigated. As structure-forming agents (SFAs), dicyandiamide (DCDA) (nitrogen source) or oxalic acid (oxygen source) or mixtures thereof were used. For characterization, cyclic voltammetry and rotating disc electrode (RDE) experiments were performed in 0.1 M H 2 SO 4 . In addition to this, N 2 sorption measurements and Raman spectroscopy were performed for the structural, and elemental analysis for chemical characterization. The role of metal, nitrogen and carbon sources within the synthesis of Fe-N-C catalysts has been pointed out before. Here, we show that the optimum in terms of ORR activity is achieved if both N-and O-containing SFAs are used in almost similar fractions. All catalysts display a redox couple, where its position depends on the fractions of SFAs. The SFA has also a strong impact on the morphology: Catalysts that were prepared with a larger fraction of N-containing SFA revealed a higher order in graphitization, indicated by bands in the 2nd order range of the Raman spectra. Nevertheless, the optimum in terms of ORR activity is obtained for the catalyst with highest D/G band ratio. Therefore, the results indicate that the presence of an additional oxygen-containing SFA is beneficial within the preparation.

Since the discovery of buckminsterfullerene in 1985,1 intensive research has been devoted to this family of closed-cage carbon nanostructures. Endohedral metallofullerene La@C60 was already detected the same year and La@C82 was isolated few years later.2 In 1999, the synthesis, isolation and characterization of the first clusterfullerene Sc3N@C80 using the Krätschmer-Huffman method was a milestone in the field of endohedral metallofullerenes (EMF).3 The characteristic structural and electronic properties of EMFs, as well as their reactivity, have been extensively analyzed by experimental and theoretical groups.4 In particular, different rules to predict the relative stability of fullerene cages, based on the ionic model, were proposed.5 A different way to modify the properties of fullerenes is by replacing a carbon atom in the caged network with a heteroatom. The resulting heterofullerene shows distinct electronic structure and, therefore, properties from the all-carbon cage precursor. Nitrogen-doped heterofullerenes have received much more attention and investigation than boron-doped heterocages.6 Few years ago, Dunk et al. reported facile gas-phase formation of C59B by atom exchange resulting from exposure of C60 to boron vapor by means of a pulsed laser vaporization cluster source, which was the first report of borafullerene formation directly from pristine C60.7 Recent application of this technique to endohedral monometallofullerenes and clusterfullerenes at the National High Magnetic Field Laboratory in Florida lead to the formation of boron-doped EMFs with exciting electronic properties. We here analyze the characteristic electronic structure of observed B-doped metalloheterofullerenes, rationalize their stabilities and discuss about their properties. References Kroto, H. W.; Heath, J. R.; O’Brien, S. C.; Curl, R. F.; Smalley, R. E. Nature 1985, 318, 162-163. a) Heath, J. R.; O’Brien, S. C.; Zhang, Q.; Liu, Y.; Curl, R. F.; Kroto, H. W.;Tittel, F. K.; Smalley, R. E. J. Am. Chem. Soc. 1985, 107, 7779-7780; (b) Chai, Y.; Cuo, T.; Jin, C.; Haufler, R. E.; Felipe Chibante, L. P.; Fure, J.; Wang, L.; Alford, J. M.; Smalley, R. E. J. Phys. Chem. 1991, 95, 7564-7568. Stevenson, S.; Rice, G.; Glass, T.; Harich, K.; Cromer, F.; Jordan, M. R.; Craft, J.; Hadju, E.; Bible, R.; Olmstead, M. M.; Maitra, K.; Fisher, A. J.; Balch, A. L.; Dorn, H. C., Nature 1999, 401, 55. a) Rodríguez-Fortea, A.; Balch, A. L.; Poblet, J. M. Chem. Soc. Rev. 2011, 40, 3551-3563; b) Popov, A. A.; Yang, S.; Dunsch, L. Chem. Rev. 2013, 113, 5989-6113. a) Rodríguez-Fortea, A.; Alegret, N.; Balch, A. L.; Poblet, J. M., Nature Chem. 2010, 2, 955-961; b) Garcia-Borràs M., Osuna S., Swart M., Luis J.M., Solà M. Angew. Chem. Int.. Ed. 2013, 52, 9275-9278; c) Wang, Y.; Díaz-Tendero, S.; Martín, F. and Alcamí, M. J. Am. Chem. Soc., 2016, 138, 1551-1560. Lamparth, I.; Nuber, B.; Schick, G.; Skiebe, A.; Grosser, T.; Hirsch, A. Angew. Chem. Int. Ed. Engl. 1995, 34, 2257. Dunk, P. W.; Rodríguez-Fortea, A.; Kaiser, N. K.; Shinohara, H.; Poblet, J. M.; Kroto, H. W. Angew. Chem. Int. Ed. 2013, 52, 315-319.

Abstract:In this work the influence of the structure forming agent on the composition, morphology and oxygen reduction reaction (ORR) activity of Fe-N-C catalysts was investigated. As structure forming agent (SFA), dicyandiamide (DCDA) (nitrogen source) or oxalic acid (oxygen source) or mixtures thereof were used. For characterization, cyclic voltammetry and rotating disc electrode (RDE) experiments were performed in 0.1 M H2SO4. In addition to this, N2 sorption measurements and Raman spectroscopy were performed for the structural characterization. The role of metal, nitrogen and carbon sources within the synthesis of Fe-N-C catalysts has been pointed out before. Here, we show that the optimum in terms of ORR activity is achieved if both N-and O-containing SFAs are used in almost similar fractions. All catalysts display a redox couple, whereat its position depends on the fractions of SFAs. The SFA has also a strong impact on the morphology: Catalysts that were prepared with a larger fraction of N-containing SFA revealed a higher order in graphitization, indicated by bands in the 2 nd order range of the Raman spectra. Nevertheless, the optimum in terms of ORR activity is obtained for the catalyst with highest D/G band ratio. Therefore, the results indicate that the presence of an additional oxygen-containing SFA is beneficial within the preparation.