Cobalt on carbon nanofiber model catalysts with very small dispersed cobalt particles of 5 nm were subjected to H(2)O/H(2) treatments at 20 bar and 220 degrees C. Using in situ Mossbauer spectroscopy we could unambiguously prove that oxidation of the nanoparticles by water will not occur when hydrogen is present. Only in a water/argon atmosphere did oxidation take place. This rules out oxidation as the deactivation mechanism in Fischer-Tropsch synthesis. Even more important, we define the relative humidity (RH) as a key parameter to understanding deactivation by water. At a RH below 25% sintering was absent even when measuring for 4 weeks, whereas at a high RH of 62% as much as half of the small super paramagnetic cobalt particles (<5 nm) sintered into larger particles in 1 week. Activity loss as measured at Fischer-Tropsch conditions amounted to 73%, which could be directly related to the metal dispersion loss 77% due to sintering as evidenced by detailed TEM analysis of the spent sample.

C–O activation is a crucial step in Fischer–Tropsch synthesis (FTS). Several pathways have been proposed to activate CO, namely, direct C–O dissociation, activation via hydrogenation, and activation by insertion into growing chains. Invariably, very high barriers are calculated for both direct C–O dissociation and for hydrogenation at the O atom in CO* and RCO*, while hydrogenation at the C atom leads to oxygenates. We demonstrate that surface hydroxyl groups open a new pathway for CO* and RCO* activation via proton transfer to the O atom. In combination with the CO insertion mechanism, the calculated rate for this new pathway is consistent with the selectivity in FTS, and is in agreement with the kinetic effect of water. Hydroxyl group formation from O* is sufficiently fast to be quasi-equilibrated, and is much faster than CO2 formation. The role of surface hydroxyl groups as hydrogenating species is likely general, and involved in several oxygenate transformation reactions.

La compounds photoelectron spectra calibration using La 4d5/2 peak as internal standard is proposed. This is demonstrated by characterizing different La compounds formed after in situ treatments on a nanorod La2O3 catalyst.

Monomeric CuII sites supported on alumina, prepared using surface organometallic chemistry, convert CH4 to CH3OH selectively. This reaction takes place by formation of CH3O surface species with the concomitant reduction of two monomeric CuII sites to CuI, according to mass balance analysis, infrared, solid‐state nuclear magnetic resonance, X‐ray absorption, and electron paramagnetic resonance spectroscopy studies. This material contains a significant fraction of Cu active sites (22 %) and displays a selectivity for CH3OH exceeding 83 %, based on the number of electrons involved in the transformation. These alumina‐supported CuII sites reveal that C−H bond activation, along with the formation of CH3O‐ surface species, can occur on pairs of proximal monomeric CuII sites in a short reaction time.