Sintering of supported cobalt nanoparticles is one of the main deactivation mechanisms in the Fischer–Tropsch synthesis. In this study, crystallite growth was studied with an alumina-supported catalyst in real time and as a function of process conditions using a novel in situ magnetometer. It could be shown that sintering with this catalyst occurred via a combination of high CO and high water partial pressures. It is proposed that particle growth proceeds via cobalt subcarbonyl migration over the hydroxylated support surface.

A study has been carried out on rhodium catalyst preforming when modified with the bulky tris(2,4-di-tert-butylphenyl) phosphite, P(Obtbp)(3). X-Ray crystal structure determinations of a tropolone-type precursor complex [Rh(TropBr(3))(CO){P(Obtbp)(3)}].P(Obtbp)(3).CH(3)COCH(3)(TropBr(3)= 3,5,7-tribromotropolonate) and the free P(Obtbp)(3) ligand are reported. Systematic in situ IR and NMR studies of the particular rhodium phosphite modified catalyst and its precursors have led to the identification of two distinct rhodium hydride species. A {(1)H,(31)P} HMBC NMR experiment afforded clarity on the (31)P NMR spectra observed under hydroformylation conditions. The species were identified as [HRh(CO)(3){P(Obtbp)(3)}] and [HRh(CO)(2){P(Obtbp)(3)}(2)]. Attention was also given to the rate of catalyst formation when starting from different rhodium precursors.

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Out with convention! The use of borosalicylic acid, derived from boric and salicylic acids, as the acid promoter in the methoxycarbonylation of ethylene to give methyl propionate has been investigated (see scheme). Not only was moderate catalyst activity observed, but much lower formation of phosphonium salts occurred than with conventional acids.

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Hagg carbide (χ-Fe 5 C 2 ) is considered to be the primary active phase for high-temperature iron-based Fischer− Tropsch synthesis (HTFTS). Hagg carbide may be oxidized to magnetite during FTS depending on the chemical potential of oxygen, μ O , which may be related to the partial pressure of the oxidizing agents, H 2 O or CO 2 . 3Fe 5 C 2 + 26H 2 O → 5Fe 3 O 4 + 6CO + 26H 2 , and 3Fe 5 C 2 + 26CO 2 → 5Fe 3 O 4 + 32CO. Magnetite is believed to be active for the water−gas shift reaction but inactive for the HTFTS, and thus, its formation could subsequently contribute to the loss in the FT activity. An in situ magnetometer was used to follow the oxidation behavior of Hagg carbide by either H 2 O or CO 2 under realistic high-temperature FT process conditions. Hagg carbide is not magnetic at the high temperature used for the FT process, while magnetite is. Thus, the transformation of Hagg carbide to magnetite can be followed by tracking its magnetization and by employing in situ X-ray diffraction, at relevant conditions. The results indicated that the oxidation of Hagg carbide and the concurrent catalyst deactivation at these conditions are strongly dependent on the H 2 O levels present in the reactor. No oxidation was observed at CO 2 levels up to 8 bar, while in agreement with the thermodynamic calculations conducted in this study, H 2 O-induced oxidation was observed at 4 bar during 3 to 20 h exposure. It may be speculated that lower H 2 O levels could also contribute to Hagg carbide oxidation if the exposure times are longer. Magnetite can be transformed back to Hagg carbide upon lowering the H 2 O partial pressure or if H 2 O is removed altogether. This fast reversibility in the phase transformation has also been coupled with an activity gain. More importantly, it has been shown that magnetite may not be solely responsible for the water−gas shift activity during the FTS.

Unkonventionell! Die Verwendung von Borosalicylsäure, die sich aus Bor‐ und Salicylsäure ableitet, als saurer Beschleuniger der Methoxycarbonylierung von Ethen zu Methylpropionat wurde untersucht (siehe Schema). Dabei wurde nicht nur eine akzeptable Katalysatoraktivität festgestellt, sondern auch eine viel geringere Bildung von Phosphoniumsalzen als mit konventionellen Säuren.