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Gonzalez-Carballo J.M.,Institute Catalisis y Petroleoquimica | Perez-Alonso F.J.,Institute Catalisis y Petroleoquimica | Ojeda M.,Institute Catalisis y Petroleoquimica | Garcia-Garcia F.J.,Complutense University of Madrid | And 2 more authors.

This work assesses the effect of the particle size for the Fischer-Tropsch synthesis with catalysts based on Ru particles between 4 and 71 nm. CO dissociation is a structure-sensitive reaction, that is, the turnover frequency (TOF) is affected by Ru particle size. Herein it is demonstrated that two regimes exist for the effect of Ru particle size. On the one hand, the expected relationship of TOF with particle size, that is, the TOF increases with Ru particles <10 nm, is only observed if measured at steady-state conditions. On the contrary, the TOF increases constantly with Ru particle size if measured at the initial state. However, the TOF measured for catalysts with Ru particles >10 nm declines during time on stream. These observations suggest that two regimes for the measurement of CO dissociation exist during Fischer-Tropsch synthesis. The reason for this is that two sites for CO dissociation on the Ru particles >10 nm exist at the initial state, terraces and step-edges, but the latter ones deactivate during time on stream. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Guerrero-Perez M.O.,University of Malaga | Rojas-Garcia E.,Metropolitan Autonomous University | Rojas-Garcia E.,Institute Catalisis y Petroleoquimica | Lopez-Medina R.,Metropolitan Autonomous University | And 2 more authors.
Catalysis Letters

Abstract: Catalysts from three different catalytic systems, Ni–Nb–O, Mo–V–Nb–Te–O and Sb–V–O, have been prepared, characterized, and tested during both ethane and propane ammoxidation reactions, in order to obtain acetonitrile and acrylonitrile, respectively. The catalytic results show that Mo–V–Nb–Te–O and Sb–V–O catalyze propane ammoxidation but are inactive for ethane ammoxidation whereas Ni–Nb–O catalysts catalyze both, ethane and propane ammoxidation. The activity results, and the characterization of fresh and used catalysts along with some data from previous studies, indicate that the ammoxidation reaction mechanism that occurs in these catalytic systems is different. In the case of Mo–V–Nb–Te–O and Sb–V–O, two active sites appear to be involved. In the case of Ni–Nb–O catalysts, only one site seems to be involved, which underlines that the mechanism is different and take place via a different intermediate. These catalysts activate the methyl groups in ethane, on the contrary, neither ethane nor ethylene appear to adsorb on the Mo–V–Nb–Te–O and Sb–V–O active sites. Graphical Abstract: [Figure not available: see fulltext.] © 2016 Springer Science+Business Media New York Source

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