Characterization by 27Al NMR, X-ray absorption spectroscopy, and density functional theory techniques of the species responsible for benzene hydrogenation in Y zeolite-supported carburized molybdenum catalysts.
Carburized molybdenum catalysts supported on a dealuminated NaH-Y zeolite were prepared by carburization under a 20% methane in hydrogen flow of two precursors obtained by adsorption of molybdenum hexacarbonyl, one containing 5 wt % and the other 10 wt % Mo, and a third one was prepared by impregnation with aqueous ammonium heptamolybdate, containing 5 wt % Mo. The three catalysts displayed very distinct behaviors in the benzene hydrogenation reaction at atmospheric pressure and 363 K. By using XANES spectroscopy at the molybdenum L edge, EXAFS and XANES spectroscopy at the molybdenum K edge, and 27Al solid-state NMR spectroscopy, it was shown that different carburized molybdenum species exist in each sample. In the catalyst containing 10 wt % Mo, formation of molybdenum carbide nanoparticles was observed, with an estimated diameter of 1.8 nm. In the catalyst containing 5 wt % Mo and prepared by carburization of adsorbed molybdenum hexacarbonyl, formation of molybdenum oxycarbide dimers is proposed. In the latter case, density functional theory calculations have led to a dimer structure which is compatible with EXAFS results. In the catalyst prepared by impregnation with ammonium heptamolybdate solution followed by carburization, the molybdenum seems to interact with extraframework alumina to produce highly disordered mixed molybdenum-aluminum oxycarbides.
Rocha
Angela S
AS
Departamento de Físico-Química and Departamento de Química Inorgânica, Instituto de Química, UFRJ, Ilha do Fundão, CT, Bloco A, Rio de Janeiro, RJ, CEP 21949-900, Brazil.
da Silva
Victor Teixeira
VT
Eon
Jean G
JG
de Menezes
Sônia M C
SM
Faro
Arnaldo C
AC
Rocha
Alexandre B
AB
D000535:Aluminum / Q000737:chemistry*; D001554:Benzene / Q000737:chemistry*; D017554:Carbon Compounds, Inorganic / Q000737:chemistry*; D002384:Catalysis; D006865:Hydrogenation; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008956:Models, Chemical; D008982:Molybdenum / Q000737:chemistry*; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis / Q000379:methods; D014965:X-Rays; D017641:Zeolites / Q000737:chemistry*
D017554:Carbon Compounds, Inorganic; D017641:Zeolites; D008982:Molybdenum; D000535:Aluminum; D001554:Benzene